The
The collection
collection ofof review
review articles
articlesProgress
in Earthand Planetary
Science(the 4th edition: published from April 2014 to February 2024)

Japan Geoscience Union（JpGU）Open Access journal

https://progearthplanetsci.springeropen.com/

CONTENTS
1. Space and planetary sciences
Space and atmospheric physics on Svalbard: a case for continued incoherent scatter radar measurements
under the cusp and in the polar cap boundary region ........................................................................................  2
Enstatite Chondrites: Condensation and Metamorphism under Extremely Reducing Conditions andContributions to the Earth ....................................................................................................................................  3
Natural and experimental high-pressure, shock-produced terrestrial and extraterrestrial materials ..................  4
Earth-affecting solar transients: a review of progresses in solar cycle 24 .........................................................  5
Role Of the Sun and the Middle atmosphere / thermosphere / ionosphere In Climate (ROSMIC):
a retrospective and prospective view ..................................................................................................................  6
Solar evolution and extrema: current state of understanding of long-term solar variability and its planetaryimpacts .................................................................................................................................................................  7
Terrestrial planet compositions controlled by accretion disk magnetic field .......................................................  8
Dynamics of the terrestrial radiation belts: A review of recent results during VarSITI (Variability of the Sun
and Its Terrestrial Impact) era, 2014-2018 ..........................................................................................................  9
A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial
Impact ................................................................................................................................................................  10
Review of the accomplishments of Mid-latitude Super Dual Auroral Radar Network (SuperDARN)HF Radars ............................................................................................................................................................ 11
Scientific innovations from the Mars aerosol optical depth based on satellite data with a temporal
resolution of hours ............................................................................................................................................... 12
Simulation study of near-Earth space disturbances: 1. Magnetic storms ........................................................... 13
Simulation study of near-Earth space disturbances: 2. Auroral substorms ........................................................ 14
Day-to-day and short-term variabilities in the equatorial plasma bubble/spread F irregularity seeding anddevelopment ........................................................................................................................................................ 15
Asteroid Ryugu before the Hayabusa2 encounter .............................................................................................. 16
Review of the generation mechanisms of post-midnight irregularities in the equatorial and low-latitude
ionosphere ........................................................................................................................................................... 17
Lightning detection on Venus: a critical review ................................................................................................... 18
Post-sunset rise of equatorial F layer—or upwelling growth? ............................................................................ 19
Effects of the postsunset vertical plasma drift on the generation of equatorial spread F .................................. 20
A review on the numerical simulation of equatorial plasma bubbles toward scintillation evaluation andforecasting ........................................................................................................................................................... 21
Mars core structure — concise review and anticipated insights from InSight .................................................... 22
Extreme geomagnetically induced currents ........................................................................................................ 23
Magnetohydrodynamics Modeling of Coronal Magnetic Field and Solar Eruptions Based on the
Photospheric Magnetic Field ............................................................................................................................... 24
MF and HF radar techniques for investigating the dynamics and structure of the 50 to 110 km heightregion: a review ................................................................................................................................................... 25
Advancing the understanding of the Sun-Earth interaction - the Climate and Weather of the Sun-Earth
System (CAWSES) II Program ............................................................................................................................ 26
The science case for the EISCAT_3D radar ....................................................................................................... 27
Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II
period ................................................................................................................................................................... 28―i―eScience and Informatics for International Science Programs ........................................................................... 29
What is the solar influence on climate? Overview of activities during CAWSES-II ............................................ 30
Response of the mesosphere-thermosphere-ionosphere system to global change– CAWSES-II contribution ................................................................................................................................... 31
The geospace response to variable inputs from the lower atmosphere: A review of the progress made by
Task Group 4 of CAWSES-II ............................................................................................................................... 32

2. Atmospheric and hydrospheric sciences
Recent global nonhydrostatic modeling approach without using a cumulus parameterization to understandthe mechanisms underlying cloud changes due to global warming .................................................................  34
Greenhouse gases observing satellite 2 (GOSAT-2): Mission overview ..........................................................  35
Climate-relevant properties of black carbon aerosols revealed by in situ measurements: a review ...............  36
The response of the hydrological cycle to temperature changes in recent and distant climatic history ............ 37
Marine microplastics as vectors of major ocean pollutants and its hazards to the marine ecosystem andhumans ................................................................................................................................................................ 38
Applications of soft computing models for predicting sea surface temperature: a comprehensive review
and assessment ................................................................................................................................................... 39
Two decades of Earth system modeling with an emphasis on Model for Interdisciplinary Research on
Climate (MIROC) ................................................................................................................................................. 40
d4PDF: large-ensemble and high-resolution climate simulations for global warming risk assessment ............. 41
DYAMOND: The DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains .... 42
Toward reduction of the uncertainties in climate sensitivity due to cloud processes using a global
non-hydrostatic atmospheric model ..................................................................................................................... 43
Maritime continent coastlines controlling Earth’s climate .................................................................................... 44
Outcomes and challenges of global high-resolution non-hydrostatic atmospheric simulations using
the K computer .................................................................................................................................................... 45
A review of atmospheric chemistry observation at mountain sites ..................................................................... 46
A review of progress towards understanding the transient global mean surface temperature response toradiative perturbation ........................................................................................................................................... 47
Overview of the development of the Aerosol Loading Interface for Cloud microphysics
In Simulation (ALICIS) ......................................................................................................................................... 48
The dynamics of the mesosphere and lower thermosphere: a brief review ....................................................... 49
Modeling in Earth system science up to and beyond IPCC AR5 ....................................................................... 50
The Non-hydrostatic Icosahedral Atmospheric Model: Description and Development ....................................... 51

3. Human geosciences・Biogeosciences
Geomorphological processes and their connectivity in hillslope, fluvial, and coastal areas in Bangladesh:
A review ............................................................................................................................................................... 54
A review of theoretical salt weathering studies for stone heritage ..................................................................... 55
Arsenic cycling in the Earth’s crust and hydrosphere: interaction between naturally occurring arsenic andhuman activities ................................................................................................................................................... 56
Geological history of the land area between Okinawa Jima and Miyako Jima of the Ryukyu Islands, Japan,
and its phylogeographical significance for the terrestrial organisms of these and adjacent islands ................  57
Accessing the energy-limited and sparsely populated deep biosphere: achievements and ongoingchallenges of available technologies .................................................................................................................  58― ii ―

Liquid and supercritical CO2 as an organic solvent in Hadean seafloor hydrothermal systems:
implications for prebiotic chemical evolution ....................................................................................................... 59
Perspective on the response of marine calcifiers to global warming and ocean acidification– Behavior of corals and foraminifera in a high CO2 world “hot house” ............................................................. 60
Theoretical constraints of physical and chemical properties of hydrothermal fluids on variations inchemolithotrophic microbial communities in seafloor hydrothermal systems. .................................................... 61
Biochemical and physiological bases for the use of carbon and nitrogen isotopes in environmental andecological studies ................................................................................................................................................ 62

4. Solid earth sciences
Reconsideration of the energy balance in earthquake faulting .........................................................................  64
An introductory review of the thermal structure of subduction zones: II—numerical approach and validation .......  65
Recent progress in research on source processes of great earthquakes using tsunami data ........................  66
An introductory review of the thermal structure of subduction zones: III—Comparison between models andobservations .......................................................................................................................................................  67
Seismic noise between 0.003 Hz and 1.0 Hz and its classification .................................................................  68
The nature of the Pacific plate as subduction inputs to the northeastern Japan arc and its implication for
subduction zone processes ...............................................................................................................................  69
Progress in modeling the Tohoku-oki megathrust earthquake cycle and associated crustal deformation
processes ...........................................................................................................................................................  70
An introductory review of the thermal structure of subduction zones: I—motivation and selected examples .....  71
Si- versus Mg-metasomatism at the crust–mantle interface: Insights from experiments, naturalobservations and geochemical modeling ..........................................................................................................  72
Progress and application of the synthesis of trans-oceanic tsunamis ..............................................................  73
Heterogeneous rheology of Japan subduction zone revealed by postseismic deformation of the 2011
Tohoku-oki earthquake ......................................................................................................................................  74
Significance of the high-pressure properties and structural evolution of gas hydrates for inferring
the interior of icy bodies ...................................................................................................................................... 75
A review on slow earthquakes in the Japan Trench ........................................................................................... 76
The role of hydrogen bonds in hydrous minerals stable at lower mantle pressure conditions .......................... 77
Fluids and physicochemical properties and processes in the Earth ................................................................... 78
DigitSeis: Software to Extract Time Series from Analogue Seismograms .......................................................... 79
Review of the Early–Middle Pleistocene boundary and Marine Isotope Stage 19 ............................................. 80
Visualizing heterogeneities of earthquake hypocenter catalogs: modeling, analysis, and compensation ......... 81
Strength models of the terrestrial planets and implications for their lithospheric structure and evolution ......... 82
Deep mantle melting, global water circulation and its implications for the stability of the ocean mass ............ 83
A coupled core-mantle evolution: Review and future prospects ......................................................................... 84
Some remarks on hydrogen-assisted electrical conductivity in olivine and other minerals ............................... 85
Detection of repeating earthquakes and their application in characterizing slow fault slip ................................ 86
Nitrogen in the Earth: abundance and transport ................................................................................................. 87
Earthquake Early Warning: what does “seconds before a strong hit” mean? .................................................... 88
Redox-controlled mechanisms of C and H isotope fractionation between silicate melt and COH fluidin the Earth’s interior ............................................................................................................................................ 89
Nonlinear dynamical analysis of GNSS data: quantification, precursors and synchronization .......................... 90― iii ―

Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California:
insight into mélange origins and subduction-accretion processes ...................................................................... 91
Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes .................. 92
Imaging in 3D under pressure: a decade of high-pressure X-ray microtomography development at
GSECARS ............................................................................................................................................................ 93
Philippine Sea Plate inception, evolution and consumption with special emphasis on the early stages of
Izu-Bonin-Mariana subduction ............................................................................................................................. 94
Mantle hydration and Cl-rich fluids in the subduction forearc ............................................................................. 95
Iron snow, crystal floats, and inner-core growth: modes of core solidification and implications for
dynamos in terrestrial planets and moons .......................................................................................................... 96
Liquid Sodium Models of the Earth’s Core .......................................................................................................... 97
Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary
dynamos .............................................................................................................................................................. 98
Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison withseismic models .................................................................................................................................................... 99
Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms ............................. 100
Water-melt interaction in hydrous magmatic systems at high temperature and pressure ............................... 101

5. Interdisciplinary research
Identifying key processes and sectors in the interaction between climate and socio-economic systems:
a review toward integrating Earth–human systems .......................................................................................... 104
Coupling library Jcup3: its philosophy and application ..................................................................................... 105
Morphometric measurements of bedrock rivers at different spatial scales and applications togeomorphological heritage research ................................................................................................................. 106
Northern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change
in the twenty-first century .................................................................................................................................. 107
Cenozoic sedimentary records of climate-tectonic coupling in the Western Himalaya .................................... 108
Transitional changes in microfossil assemblages in the Japan Sea from the Late Pliocene to
Early Pleistocene related to global climatic and local tectonic events ............................................................. 109
Evolution and variability of the Asian monsoon and its potential linkage with uplift of the Himalaya andTibetan Plateau .................................................................................................................................................. 110
Geochemical approaches to the quantification of dispersed volcanic ash in marine sediment ....................... 111
Sea surface temperature proxies (alkenones, foraminiferal Mg/Ca, and planktonic foraminiferal assemblage)
and their implications in the Okinawa Trough ................................................................................................... 112
Marine tephra in the Japan Sea sediments as a tool for paleoceanography and paleoclimatology ................ 113
The Pliocene to Recent History of the Kuroshio and Tsushima Currents: a multi-proxy approach ................. 114― iv ―

Review
Space and planetary sciences

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Space and atmospheric physics on Svalbard: a case for continued incoherent scatter radarmeasurements under the cusp and in the polar cap boundary region
Lisa Baddeley, Dag Lorentzen, Stein Haaland, Erkka Heino, Ingrid Mann, Wojciech Miloch, Kjellmar Oksavik,
Noora Partamies, Andres Spicher, Juha Vierinen[Keywords] Ionosphere, Atmospheric science, Space weather, Cusp, Polar cap, Plasma turbulence, Space debris,
Incoherent scatter radar, Atmospheric escape

Incoherent scatter radars (ISRs) represent the only
instrument (both ground and space based) capable ofmaking high temporal and spatial resolution measurementsof multiple atmospheric parameters—such as densities,
temperatures, particle velocities, mass flux—over analtitude range covering the entire mesosphere/lower
thermosphere/ionosphere (MLTI) system on a quasicontinuous basis. The EISCAT Svalbard incoherent
scatter radar (ESR), located just outside Longyearbyen(78.15°N) on Svalbard, is the only currently operating
facility capable of making such measurements inside thepolar cusp—an area of significant energy input into theatmosphere and characterized by heating instabilities andturbulence. The ESR was built in the mid-1990s and has
provided valuable data for the international experimental and modelling communities. New radar technologies are now
available, in the form of phased array systems, which offer new data products and operational flexibility. This paper
outlines the achievements and current research focus of the ESR and provides scientific arguments, compiled from
inputs across the international scientific community, for a new phased array ISR facility on Svalbard. In addition to thefundamental scientific arguments, the paper discusses additional benefits of continued ISR observations on Svalbard,
building on the key findings of the ESR. Svalbard has a large network of complementary instrumentation both focusedon the MLTI system (e.g. the Kjell Henriksen auroral Observatory, the Svalbard SuperDARN radar and the Svalrak
sounding rocket launch facility) with synergies to other research fields, such as meteorology and oceanography. As afurther holistic system science view of the Earth becomes more important, a new ISR on Svalbard will be importantalso in this respect with its ability to provide datasets with a wide range of scientific applications. Increased activity inspace has highlighted problematic issues such as space debris. A changing Arctic has also seen increased humanactivity via the opening up of new shipping routes, which are reliant on GNSS technology that is effected by severe
turbulence in the MLTI system. As such, societal applications of a future ISR are also presented. The accessibility
and logistical support for such a facility is also briefly discussed.

Published: 2023/9/4
https://doi.org/10.1186/s40645-023-00585-9―2―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Enstatite Chondrites: Condensation and Metamorphism under Extremely Reducing Conditions
and Contributions to the Earth
Yangting Lin[Keywords] enstatite chondrite, condensation of the solar nebula, reducing conditions, inner solar system, building
blocks of the EarthEnstatite chondrites are a small clan of meteorites,
only ~ 1% out of all meteorite collection. However, they
are the most reduced meteorites and have almost identicalisotopic compositions to those of the Earth, suggestive ofsignificant contributions to the latter and other terrestrial
planets. Enstatite chondrites contain a unique mineralinventory of sulfides of typical lithophile elements,
Si-bearing metal, silicide and phosphide, which record
the nebular processes and the thermal metamorphism inasteroidal bodies under extremely reducing environments.
EH group is mainly characteristic of the higher Si content
of metallic Fe–Ni and the higher MnS contents of sulfides
than EL group, indicative of a more reducing condition thanthe latter. However, the fugacity pH2S could be the same
in both EH and EL regions, because it was buffered by

The compositions of (Mg,Mn,Fe)S, a key indicator for condensation and metamorphism of enstatite chondrites

kamacite and troilite. The majority of sulfides condensed
from the nebula, partially enclosing schreibersite micron-spherules formed probably by early melting. Another part oftroilite, sphalerite and djerfisherite, intergrown with perryite, were produced via sulfidation of metallic Fe–Ni. Minor
exotic components were also found in enstatite chondrites, including Ca-, Al-rich inclusions and FeO-rich silicate clasts.
The Ca-, Al-rich inclusions are identical to those in carbonaceous chondrites except for the alteration under reducing
environments, and the FeO-rich silicate clasts show reduction reactions, both suggestive of migration of dust in the
protoplanetary disk. The highly reducing conditions (as C/O ratios) might be established via repeating evaporationand condensation of water ice and organic matter across the snow line along the protoplanetary disk, but need tofind evidence. Another issue is the preservation of submicron-to-micron-sized presolar grains during high-temperaturecondensation of the major constituent minerals. After accretion, the parent bodies of EH and EL chondrites probably
experienced distinct thermal histories, indicated by their distinct petrologic-type distributions and different correlations
with the closure temperatures determined by the FeS contents of sulfides in contact with troilite.
The composition of (Mg, Mn, Fe)S, a key indicator for condensation and metamorphism of enstatite chondrites.

Published: 2022/5/20
https://doi.org/10.1186/s40645-022-00483-6―3―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Natural and experimental high-pressure, shock-produced terrestrial and extraterrestrial materials
Masaaki Miyahara, Naotaka Tomioka, Luca Bindi[Keywords] High-pressure mineral, Shock metamorphism, Meteorite, Impact crater

Hypervelocity impacts are among the fundamental
phenomena occurring during the evolution of the solar
system and are characterized by instantaneous ultrahighpressure and temperature. Varied physicochemicalchanges have occurred in the building blocks of celestialbodies under such extreme conditions. The constituent
material has transformed into a denser form, a highpressure polymorph. The high-pressure polymorph isalso thought to be the constituent of the deep Earth’s
interior. Hence, experiments using a high-pressure andtemperature generating apparatus have been conducted
to clarify its crystal structure, pressure-temperaturestability range, and transformation mechanisms. A natural
high-pressure polymorph (mineral) is found from terrestrial
and extraterrestrial rocks that experienced a hypervelocity
impact. Mineralogists and planetary scientists have

A meteorite with shock-induced melting and high-pressuremineral.

investigated high-pressure minerals in meteorites androcks near terrestrial craters over a half-century. Here,
we report brief reviews about the experiments producing
high-pressure polymorphs and then summarize theresearch histories of high-pressure minerals occurringin shocked meteorites and rocks near terrestrial craters.
Finally, some implications of high-pressure minerals foundin impact-induced shocked rocks are also mentioned.

Published: 2021/10/18
https://doi.org/10.1186/s40645-021-00451-6―4―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Earth-affecting Solar Transients: A Review of Progresses in Solar Cycle 24
Jie Zhang, Manuela Temmer, Nat Gopalswamy, Olga Malandraki, Nariaki V. Nitta, Spiros Patsourakos, Fang
Shen, Bojan Vrsnak, Yuming Wang, David Webb, Mihir Desa, Karin Dissauer, Nina Dresing, Mateja Dumbovic,
Xueshang Feng, Stephan Heinemann, Monica Laurenza, Noe Lugaz, Bin Zhuang[Keywords] Coronal Mass Ejection, Interplanetary Coronal Mass Ejection, Solar Energetic Particle, Corotating
Interaction Region, Flare, Corona, Sun, Geomagnetic Storms, Space Weather

This review article summarizes theadvancement in the studies of Earth-affecting solar transients in the last decade thatencompasses most of solar cycle 24. It is apart of the effort of the International Studyof Earth-affecting Solar Transients (ISEST)
project, sponsored by the SCOSTEP/VarSITI program (2014-2018). The Sun-Earthis an integrated physical system in which
the space environment of the Earth sustains
continuous influence from mass, magnetic
field, and radiation energy output of the Sunin varying timescales from minutes to millennium. This article addresses short timescale
events, from minutes to days that directly
cause transient disturbances in the Earth’s
space environment and generate intense

A schematic of CMEs (lower, center) from the Sun to the Earth. Their man-adverse effects on advanced technologicalifestations near the Sun (upper left) and at 1 AU (upper right) both contain asystems of human society. Such transient

shock-sheath component (red) and flux rope component (blue)

events largely fall into the following fourtypes: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar
energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions(CIRs). In the last decade, the unprecedented multi-viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided
much more accurate and global measurements of the size, speed, propagation direction, and morphology of CMEs inboth 3D and over a large volume in the heliosphere. Many CMEs, fast ones, in particular, can be clearly characterized
as a two-front (shock front plus ejecta front) and three-part (bright ejecta front, dark cavity, and bright core) structure.
Drag-based kinematic models of CMEs are developed to interpret CME propagation in the heliosphere and are applied
to predict their arrival times at 1 AU in an efficient manner. Several advanced MHD models have been developed
to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been
made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformationof CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also
been significantly improved. An outlook of how to address critical issues related to Earth-affecting solar transientsconcludes this article.

Published: 2021/10/5
https://doi.org/10.1186/s40645-021-00426-7―5―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Role Of the Sun and the Middle atmosphere / thermosphere / ionosphere In Climate (ROSMIC):
a retrospective and prospective view
Ward W, Seppälä A, Yiğit E, Nakamura T, Stolle C, Laštovička J, Woods TN, Tomikawa Y, Lübken FJ, Solomon
SC, Marsh DR, Funke B, Pallamraju D[Keywords] Climate, Atmosphere, Middle atmosphere, Thermosphere, Ionosphere, Solar irradiance, Energetic
particles, Atmospheric coupling, Trends

While knowledge of the energy inputs fromthe Sun (as it is the primary energy source) is
important for understanding the solar-terrestrial system, of equal importance is the manner in which the terrestrial part of the systemorganizes itself in a quasi-equilibrium state toaccommodate and re-emit this energy. The
ROSMIC project (2014-2018 inclusive) was
the component of SCOSTEP’s Variability of the
Sun and Its Terrestrial Impact (VarSITI) program
which supported research into the terrestrial
component of this system. The four themes

Links in the middle atmosphere. A schematic showing the relationshipsupported under ROSMIC are solar influence

between various components affecting the large-scale structure of theon climate, coupling by dynamics, trends in the

middle atmosphere. The main elements appear in the green boxes, andmesosphere lower thermosphere, and trends

the processes linking them appear in the blue boxes. The arrows indicate

and solar influence in the thermosphere. Overthe direction of the influence.

the course of the VarSITI program, scientificadvances were made in all four themes. This included improvements in understanding (1) the transport of photochemically produced species from the thermosphere into the lower atmosphere; (2) the manner in which waves produced in
the lower atmosphere propagate upward and influence the winds, dynamical variability, and transport of constituentsin the mesosphere, ionosphere, and thermosphere; (3) the character of the long-term trends in the mesosphere andlower thermosphere; and (4) the trends and structural changes taking place in the thermosphere. This paper reviews
the progress made in these four areas over the past 5 years and summarizes the anticipated research directions inthese areas in the future. It also provides a physical context of the elements which maintain the structure of the terrestrial component of this system. The effects that changes to the atmosphere (such as those currently occurring asa result of anthropogenic influences) as well as plausible variations in solar activity may have on the solar terrestrial
system need to be understood to support and guide future human activities on Earth.

Published: 2021/8/18
https://doi.org/10.1186/s40645-021-00433-8―6―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Solar evolution and extrema: current state of understanding of long-term solar variability and its
planetary impacts
Nandy D., Martens P.C.H., Obridko V., Dash S., Georgieva K.
[Keywords] Solar magnetic fields, Stellar evolution, Stellar flares, Stellar wind, Space weather, Space climate, Faint
Young Sun paradox, Star planet interactions, Planetary evolution, Habitability

The activity of stars such as the Sun varies overtimescales ranging from the very short to the very longstellar and planetary evolutionary timescales. Experiencefrom our solar system indicates that short-term, transient
events such as stellar flares and coronal mass ejections
create hazardous space environmental conditions that
impact Earth-orbiting satellites and planetary atmospheres.
Extreme events such as stellar superflares may play a role inatmospheric mass loss and create conditions unsuitable forlife. Slower, long-term evolutions of the activity of Sun-like

Stellar wind–planet interactions

stars over millennia to billions of years result in variations
in stellar wind properties, radiation flux, cosmic ray flux, and frequency of magnetic storms. This coupled evolution ofstar-planet systems eventually determines planetary and exoplanetary habitability. The Solar Evolution and Extrema(SEE) initiative of the Variability of the Sun and Its Terrestrial Impact (VarSITI) program of the Scientific Committee
on Solar-Terrestrial Physics (SCOSTEP) aimed to facilitate and build capacity in this interdisciplinary subject of broadinterest in astronomy and astrophysics. In this review, we highlight progress in the major themes that were the focusof this interdisciplinary program, namely, reconstructing and understanding past solar activity including grand minima
and maxima, facilitating physical dynamo-model-based predictions of future solar activity, understanding the evolutionof solar activity over Earth’s history including the faint young Sun paradox, and exploring solar-stellar connections withthe goal of illuminating the extreme range of activity that our parent star-the Sun-may have displayed in the past, or
may be capable of unleashing in the future.

Published: 2021/7/5
https://doi.org/10.1186/s40645-021-00430-x―7―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Terrestrial planet compositions controlled by accretion disk magnetic field
William F McDonough, Takashi Yoshizaki[Keywords] planetary formation, planetary composition, accretionary disk, magnetic field

Terrestrial planets (Mercury, Venus, Earth,and Mars) are differentiated into three layers:a metallic core, a silicate shell (mantle andcrust), and a volatile envelope of gases, ices,and, for the Earth, liquid water. Each layer has
different dominant elements (e.g., increasingiron content with depth and increasing oxygen
content to the surface). Chondrites, the building
blocks of the terrestrial planets, have mass andatomic proportions of oxygen, iron, magnesium,and silicon totaling ≥ 90% and variable Mg/Si(∼ 25%), Fe/Si (factor of ≥2), and Fe/O (factorof ≥ 3). What remains an unknown is to what
degree did physical processes during nebular

Density of the rocky solar system bodies. Uncompressed and solid den-disk accretion versus those during post-nebular

sities are shown for terrestrial planets and chondrites (grey), respectively.

disk accretion (e.g., impact erosion) influence

Bulk planetary densities are shown for asteroids (blue).

these planets final bulk compositions. Here we
predict terrestrial planet compositions and show that their core mass fractions and uncompressed densities correlatewith their heliocentric distance, and follow a simple model of the magnetic field strength in the protoplanetary disk. Ourmodel assesses the distribution of iron in terms of increasing oxidation state, aerodynamics, and a decreasing magnetic
field strength outward from the Sun, leading to decreasing core size of the terrestrial planets with radial distance. This
distribution enhances habitability in our solar system and may be equally applicable to exoplanetary systems.

Published: 2021/7/2
https://doi.org/10.1186/s40645-021-00429-4―8―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Dynamics of the terrestrial radiation belts: A review of recent results during VarSITI (Variabilityof the Sun and Its Terrestrial Impact) era, 2014-2018
Kanekal S., Miyoshi Y.
[Keywords] Inner Magnetosphere, Energetic Particles, Plasma Waves, Wave-Particle Interactions, Radiation Belts,
Plasmasphere, Ring Current

The Earth’s magnetosphere is region thatis carved out by the solar wind as it flows pastand interacts with the terrestrial magnetic
field. The inner magnetosphere is the region
that contains the plasmasphere, ring current,
and the radiation belts all co-located within
about 6.6 Re, nominally taken to be bounding
this region. This region is highly dynamic andis home to a variety of plasma waves andparticle populations ranging in energy from a
few eV to relativistic and ultra-relativistic electrons and ions. The interplanetary magnetic
field (IMF) embedded in the solar wind via
the process of magnetic reconnection at the
sub-solar point sets up plasma convection
and creates the magnetotail. Magnetic recon-

Diagram illustrating the interconnectedness and cross-energy coupling
between particles, waves, and underlying physical processes.

nection also occurs in the tail and is responsible for explosive phenomena known as substorms. Substorms inject low-energy particles into the inner magnetosphereand help generate and sustain plasma waves. Transients in the solar wind such as coronal mass ejections (CMEs),
co-rotating interaction regions (CIRs), and interplanetary shocks compress the magnetosphere resulting in geomagnetic storms, energization, and loss of energetic electrons in the outer radiation belt nad enhance the ring current,
thereby driving the geomagnetic dynamics. The Specification and Prediction of the Coupled Inner-Magnetospheric
Environment (SPeCIMEN) is one of the four elements of VarSITI (Variability of the Sun and Its Terrestrial Impact)
program which seeks to quantitatively predict and specify the inner magnetospheric environment based on Sun/solar
wind driving inputs. During the past 4 years, the SPeCIMEN project has brought together scientists and researchers
from across the world and facilitated their efforts to achieve the project goal. This review provides an overview ofsome of the significant scientific advances in understanding the dynamical processes and their interconnectedness
during the VarSITI era. Major space missions, with instrument suites providing in situ measurements, ground-based
programs, progress in theory, and modeling are briefly discussed. Open outstanding questions and future directionsof inner magnetospheric research are explored.

Published: 2021/5/31
https://doi.org/10.1186/s40645-021-00413-y―9―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial Impact
Shiokawa K, Georgieva K[Keywords] VarSITI, Variability of the Sun and its terrestrial impact, Sun, Heliosphere, Inner magnetosphere.
Ionosphere, Thermosphere, Middle atmosphere, Climate change, Space weather

The Sun is a variable active-dynamo star, emitting radiation in all wavelengths and solar-wind plasma to the interplanetary space. The Earth is immersed in this radiation and solar wind, showing various responses in geospace andatmosphere. This Sun-Earth connection variates in time scales from milli-seconds to millennia and beyond. The solar
activity, which has a ~11-year periodicity, is gradually declining in recent three solar cycles, suggesting a possibilityof a grand minimum in near future. VarSITI-variability of the Sun and its terrestrial impact-was the 5-year programof the scientific committee on solar-terrestrial physics (SCOSTEP) in 2014-2018, focusing on this variability of the
Sun and its consequences on the Earth. This paper reviews some background of SCOSTEP and its past programs,
achievements of the 5-year VarSITI program, and remaining outstanding questions after VarSITI.

Fig1: Logo of the VarSITI program

Fig2: Black: challenging scientific topics in the solar-terrestrial coupling
during and after the VarSITI program. Red: their consequences on human
life. Short and long-term variabilities are shown in the left and right sideof the figure, respectively. CIR corotating interaction region, CME coronalmass ejection, CR cosmic ray, IMF interplanetary magnetic field, GNSS
global navigation satellite system, GW gravity wave, MHD magnetohydrodynamics, PW planetary wave, UV ultraviolet

Published: 2021/3/9
https://doi.org/10.1186/s40645-021-00410-1― 10 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Review of the accomplishments of Mid-latitude Super Dual Auroral Radar Network (SuperDARN)HF Radars
Nishitani N, Ruohoniemi JM, Lester M, Baker JBH, Koustov AV, Shepherd SG, Chisham G, Hori T, ThomasEG, Makarevich RA, Marchaudon A, Ponomarenko P, Wild JA, Milan SE, Bristow WA, Devlin J, Miller E,
Greenwald RA, Ogawa T, Kikuchi T[Keywords] Mid-latitude SuperDARN, Ionosphere, Magnetosphere, Convection, Ionospheric irregularities, HF
propagation analysis, Ion-neutral interactions, MHD waves

The Super Dual Auroral Radar Network(SuperDARN) is a network of high-frequency(HF) radars located in the high- and mid-latitude regions of both hemispheres that is
operated under international cooperation. The
network was originally designed for monitoring the dynamics of the ionosphere and upper
atmosphere in the high-latitude regions. However, over the last approximately 15 years,
SuperDARN has expanded into the mid-latitude
regions. With radar coverage that now extends

Schematic plots showing the a Northern and b Southern Hemisphere
SuperDARN radar locations with respect to the auroral oval. The model

continuously from auroral to sub-auroral andauroral oval (yellow) for moderately disturbed conditions is plotted with

mid-latitudes, a wide variety of new scientific

the SuperDARN radar locations identified in green type and green closed

findings have been obtained. In this paper,

circles (polar cap latitudes), blue type and blue closed circles (auroral

the background of mid-latitude SuperDARN islatitudes), and black type and red closed circles (mid-latitude radars).

presented at first. Then, the accomplishments
made with mid-latitude SuperDARN radars
are reviewed in five specified scientific andtechnical areas: convection, ionospheric irregularities, HF propagation analysis, ion-neutralinteractions, and magnetohydrodynamic (MHD)
waves. Finally, the present status of mid-latitude
SuperDARN is updated and directions for future
research are discussed.

Schematic illustration of natural phenomena which can be studied bySuperDARN radars.

Published: 2019/3/18
https://doi.org/10.1186/s40645-019-0270-5― 11 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Scientific innovations from the Mars aerosol optical depth based on satellite data with a temporal resolution of hours
Gebhardt C, Abuelgasim A.
[Keywords] ExoMars Trace Gas Orbiter (TGO), Emirates Mars Mission (EMM), Mars stationary satellites, Mars
atmosphere, Aerosol optical depth, Dust, Water ice clouds, Mars climatology, Mars numerical weather forecasting,
Data assimilation

The ExoMars Trace Gas Orbiter (TGO), Emirates Mars Mission (EMM), and possible futureMars stationary satellite(s) will provide innovative data products on the optical depth of dust
and water ice clouds in the Martian atmospherewith a temporal resolution of hours. The science phase of TGO has begun in April 2018,
and the EMM science operation is scheduled
to start in 2021. In this work, the relationshipbetween TGO, EMM, and precursor missions/
instruments is analyzed based on the obtained
data products. This is followed by discussing
the foreseen innovation from the latter in the fields of Martian climatology and numerical weather forecasting.

Published: 2019/3/28
https://doi.org/10.1186/s40645-019-0276-z― 12 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Simulation study of near-Earth space disturbances: 1. Magnetic storms
Ebihara Y.
[Keywords] Magnetic storms, Computer simulation, Magnetosphere, Ionosphere, Inner magnetosphere, and Ring
current.

A magnetic storm is the world-wide geomagnetic disturbance taking place in near-Earthspace environment, lasting for a few days.
Geomagnetic fields can be depressed by ~1%on the ground for large magnetic storms. The
prime cause of the long-lasting, world-wide geomagnetic disturbance is the development of thering current that surrounds the Earth. The ring
current is an electric current carried by charged
particles. Thus, the growth and decay of the ring
current correspond to accumulation and loss of
the ring current particles, respectively. The ring
current is strong enough to modulate near-Earthspace environment, and leads to many observable effects. In this sense, the ring current can

Cross energy and cross region coupling in the inner magnetosphere andthe ionosphere.

be regarded as an important mediator in thenear-Earth space environment. Here, the dynamics and structure of the ring current and its active role are briefly
reviewed on the basis of numerical simulation results.

Published: 2019/2/13
https://doi.org/10.1186/s40645-019-0264-3― 13 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Simulation study of near-Earth space disturbances: 2. Auroral substorms
Yusuke Ebihara[Keywords] Substorm, Aurora, Computer simulation, Magnetosphere, and Ionosphere.

A substorm is a transient phenomenon thatlasts for only 1–2 h. One significant manifestation of the substorm is a sudden brightening of
the aurora on the nightside. Simultaneously, theauroral electrojets are abruptly intensified in theionosphere, disturbing the geomagnetic field in
the polar region. The near-Earth space environment is highly disturbed, which manifests as anearthward fast flow of plasma, a sudden change
in the magnetic field, or a sudden increase in
hot plasma. Such disturbances are known toseverely affect human society. The ultimate
cause of the disturbances is the solar wind,
but an explanation of the chain of processes
leading from solar wind to the ionosphere is
problematic. Here, the evolution of the auroral
substorm is reviewed based on the results ofa global magnetohydrodynamics (MHD) sim-

Conceptual illustration of possible chain reaction of an auroral substorm inulation, called a REProduce Plasma Universe

terms of energy transfer from the solar wind to the ionosphere.

(REPPU) code. The REPPU code is shown toreproduce many aspects of the auroral substorms and to be useful for understanding the primary chain processes
from the solar wind to the ionosphere.

Published: 2019/3/5
https://doi.org/10.1186/s40645-019-0273-2― 14 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Day-to-day and short-term variabilities in the equatorial plasma bubble/spread F irregularity
seeding and development
Mangalathayil Ali Abdu
[Keywords] Equatorial ionosphere, Plasma bubbles/spread F irregularities, Prereversal vertical drift, Prompt penetrationelectric field, Gravity waves, Trans-equatorial wind, Planetary/Kelvin waves, ESF/EPB short-term variability

The background ionospheric conditions
shaped by sunset electrodynamic processes
are responsible for the development of equatorial plasma bubble (EPB)/equatorial spread
F (ESF) irregularities of the post-sunset ionosphere. Distinct conditions exist for the EPB/
ESF development also at later hours of thenight. The plasma instability growth leading
to EPB generation is dependent on the basic
precursor conditions defined by the well-known
parameters: the evening prereversal enhancement in vertical plasma drift (PRE), wave structure in plasma density and polarization electricfield required to initiate/seed the instability, andthe F layer bottom side density gradient, as asignificant factor in controlling the growth rate. Competing roles of the zonal versus meridional thermospheric winds
additionally control their development. Statistical as well as case studies have addressed aspects of the EPB development and occurrence under different geophysical conditions, generally focusing attention on any one of the above
specific parameters. Little is known regarding the relative importance of concurrent presence of the precursor parameters (mentioned above) in shaping a given event. A large degree of day-to-day variability in these parameters arise
from different sources of forcing, such as upward propagating atmospheric waves, and magnetic disturbance timeelectric fields in the form of prompt penetration and disturbance dynamo electric fields that often contribute to thewidely observed short-term variabilities in EPB development and dynamics. In this paper, we will present and discuss
some important aspects of the EPB/ESF short-term variability, focusing attention on their enhanced development, or
suppression and, wherever possible, highlighting also the relative roles of the precursor parameters in such variability.

Published: 2019/2/1
https://doi.org/10.1186/s40645-019-0258-1― 15 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Asteroid Ryugu before the Hayabusa2 encounter
Wada K, Grott M, Michel P, Walsh K, Barucci A, Biele J, Blum J, Ernst C, Grundmann J, Gundlach B,
Hagermann A, Hamm M, Jutzi M, Kim M, Kührt E, Le Corre L, Libourel G, Lichtenheldt R, Maturilli A,
Messenger S, Michikami T, Miyamoto H, Mottola S, Müller T, Nakamura A, Nittler L, Ogawa K, Okada T,
Palomba E, Sakatani N, Schröder S, Senshu H, Takir D, Zolensky M and International Regolith Science
Group (IRSG) in Hayabusa2 project[Keywords] Hayabusa2, Ryugu, Asteroids, Regolith, Physical properties

Asteroid (162173) Ryugu is the target objectof Hayabusa2, an asteroid exploration andsample return mission led by Japan Aerospace
Exploration Agency (JAXA). Ground-based
observations indicate that Ryugu is a C-typenear-Earth asteroid with a diameter of lessthan 1 km, but the knowledge of its detailed
properties is very limited prior to Hayabusa2
observation. This paper summarizes our best
understanding of the physical and dynamical
properties of Ryugu based on ground-based
remote sensing and theoretical modeling before
the Hayabusa2’s arrival at the asteroid. This
information is used to construct a design reference model of the asteroid that is used forContour plot of thermal inertia (in units of J m−2 s−1/2 K−1) as a function of
typical particle diameter and porosity (see text for the regolith parametersassumed in the calculation). The gray-filled region indicates the thermal
inertia range estimated for Ryugu by ground-based observations (Müller

the formulation of mission operation plans in

et al. 2017). From this figure, we can estimate a typical particle size foradvance of asteroid arrival. Particular attention

the Ryugu regolith.

is given to the surface properties of Ryugu thatare relevant to sample acquisition. This reference model helps readers to appropriately interpret the data that will bedirectly obtained by Hayabusa2 and promotes scientific studies not only for Ryugu itself and other small bodies but
also for the solar system evolution that small bodies shed light on.

Published: 2018/12/11
https://doi.org/10.1186/s40645-018-0237-y― 16 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Review of the generation mechanisms of post-midnight irregularities in the equatorial andlow-latitude ionosphere
Otsuka Y[Keywords] Equatorial ionosphere, Ionospheric irregularity, Rayleigh–Taylor instability, Plasma bubble

This paper provides a brief review of ionospheric irregularities that occur in magneticallyequatorial and low-latitude regions post-midnight during low solar activity periods. Ionospheric irregularities can occur in equatorial
plasma bubbles. Plasma bubbles are wellknown to frequently occur post-sunset when thesolar terminator is nearly parallel to the geomagnetic field lines (during equinoxes at thelongitude where the declination of the geomagnetic field is almost equal to zero and near the
December solstice at the longitude where thedeclination is tilted westward), especially duringhigh solar activity conditions via the Rayleigh–Taylor instability. However, recent observations
during a solar minimum period show a highoccurrence rate of irregularities post-midnightaround the June solstice. The mechanisms forgenerating the post-midnight irregularities arestill unknown, but two candidates have been
proposed. One candidate is the seeding of theRayleigh–Taylor instability by atmospheric gravity waves propagating from below into the ionosphere. The other candidate is the uplift of theRange-time-intensity plot of the field-aligned irregularity (FAI) echo in the

F layer by the meridional neutral winds in the

F region observed on the five beams of a VHF radar in Indonesia on thethermosphere, which may be associated withnights of August 21, 2007. (after Otsuka et al. 2009)

midnight temperature maximums in the thermosphere.

Published: 2018/9/20
https://doi.org/10.1186/s40645-018-0212-7― 17 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Lightning detection on Venus: a critical review
Ralph D. Lorenz[Keywords] Venus, Lightning, Electromagnetic emission, Observation

Claimed detections and nondetections oflightning and related electromagnetic emissions
on Venus are qualitatively contradictory. Here,motivated by the commencement of observations by the Akatsuki spacecraft and by studies
of future missions, we critically review spacecraft and ground-based observations of thepast 40 years, in an attempt to reconcile thediscordant reports with a minimal number ofassumptions. These include invoking alternative interpretations of individual reports, guided
by sensitivity thresholds, controls, and otherobjective benchmarks of observation integrity.
The most compelling evidence is in fact the first,
the very low frequency (VLF) radio emissions
recorded beneath the clouds by all four of the
Veneras 11–13 landers, and those data are
re-examined closely, finding power-law amplitude characteristics and substantial differences
between the different profiles. It is concluded
that some kind of frequent electrical activity is supported by the preponderance of observations, but optical emissions
are not consistent with terrestrial levels of activity. Venus’ activity may, like Earth’s, have strong temporal and/or spatial
variability, which coupled with the relatively short accumulated observation time for optical measurements, can leadto qualitative discrepancies between observation reports. We note a number of previously unconsidered observations
and outline some considerations for future observations.

Published: 2018/6/2
https://doi.org/10.1186/s40645-018-0181-x― 18 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Post-sunset rise of equatorial F layer—or upwelling growth?
Tsunoda R T, Saito S, Nguyen T T[Keywords] Equatorial plasma bubbles, Equatorial spread F, Day-to-day variability, Post-sunset rise of equatorial F
layer, Large-scale wave structure, Upwelling paradigm, Upwelling growth, Pre-reversal enhancement, Electric field,
Equatorial ionosphere

According to the so-called upwelling paradigm, development of equatorial plasma bubbles (EPBs) involves (1) appearance of an
upwelling (i.e., local uplift with a zonal width of~400 km) in the bottomside of the equatorial F
layer, (2) its growth via the F-region interchange
instability during the post-sunset rise (PSSR) of
the F layer, and (3) launching of EPBs, whichstarts near the end of PSSR, from within theconfines of the upwelling. In this description, the
PSSR is presumed to be the primary driver ofthe paradigm, with upwelling growth dependent
on PSSR strength. As constructed, the paradigm describes EPB development when PSSR
is strong (i.e., high solar activity), but not when
it is weak. We, show, for the first time, that when
PSSR is weak (e.g., low solar activity), upwelling growth can still be comparable in strength
to what would be considered a strong PSSR,
and that this growth drives EPB development.
Given that EPBs do not develop outside of
upwellings, regardless of solar activity, we are
led to conclude, against mainstream thinking,that the controlling driver for EPB development
is upwelling growth, not PSSR. For continued
progress toward understanding EPB development, a crucial next step is to identify the source
mechanism for upwelling growth, especiallyCurves of h’F (2.5) vs UT, for two quiet nights (20 and 22 March 2006),
and one disturbed night (27 March 2006). The green (red) curve is for BCL(CPN). The gray curve is h’F (2.5) vs LST for CPN. Two levels for range
type of ESF are shown, weak and strong; they should be used with the
UT scale. Mean SSN for 2006 was 15.2.

when PSSR is weak, and to better understandthe complexities of the underlying physics.

Published: 2018/4/14
https://doi.org/10.1186/s40645-018-0179-4― 19 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Effects of the postsunset vertical plasma drift on the generation of equatorial spread F
Huang C-S
[Keywords] Equatorial ionosphere, Equatorial spread F, Plasma bubbles, Rayleigh-Taylor instability, Vertical plasma
drift, Prereversal enhancement

Equatorial spread F (ESF) irregularities arecaused by plasma instability processes in theequatorial ionosphere and especially related
to plasma bubble phenomena in the topside F
region. Plasma bubbles result from nonlinear
evolution of the Rayleigh-Taylor instability. The
prereversal enhancement (PRE) of the postsunset vertical plasma drift increases the heightThe dependence of the plasma bubble occurrence probability on the verti-of the equatorial F layer, creating conditions

cal ion drift at the PRE peak measured by C/NOFS during May 2008-June

conducive to the growth of the Rayleigh-Taylor

2013 for different seasons.

instability, and is an important factor that controls the generation of ESF. Three different relationships of the quantitative connection between the PRE and ESF
occurrence have been derived. (1) A threshold PRE must be reached for the occurrence of ESF. ESF will be generated
when the PRE is larger than the threshold and will not be generated when the PRE is smaller than the threshold. (2)The occurrence probability of ESF increases approximately linearly with the PRE. (3) The occurrence probability of
ESF is characterized by a continuous probability distribution as a function of the PRE magnitude. The second and third
relationships imply that the PRE can be used to specify the occurrence probability of ESF. This paper will review these
relationships and discuss how these relationships are connected to each other. The effects of seeding perturbations
on the generation and global distribution of ESF will be briefly discussed.

Published: 2018/1/9
https://doi.org/10.1186/s40645-017-0155-4― 20 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

A review on the numerical simulation of equatorial plasma bubbles toward scintillation evaluationand forecasting
Yokoyama T[Keywords] Equatorial ionosphere, Equatorial spread F, Equatorial plasma bubbles, Numerical simulation, Scintillation,
High-performance computing, Space weather

Equatorial plasma bubbles (EPBs) have beena longstanding and increasingly important subject because they cause severe scintillations inradio waves from Global Navigation Satellite
System satellites. The phenomenon was foundin the 1930s as irregular ionosonde observations and was termed equatorial spread F (ESF).
ESF is interpreted as plasma density irregularities associated with EPBs that have nonlinearly
evolved into the topside ionosphere. Numericalsimulations have been powerful tools to study
the fully nonlinear evolution of EPBs, whichcannot be wholly understood from theoreticalpredictions. In this paper, historical achievements in the numerical simulation of EPBs arereviewed, and future directions toward scintillation evaluation and forecast are discussed.

An example of numerical simulation results of equatorial plasma bubbles

Published: 2017/12/12
https://doi.org/10.1186/s40645-017-0153-6― 21 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Mars core structure — concise review and anticipated insights from InSight
Helffrich G[Keywords] Mars, InSight, Dynamo, Core, Fe-FeS phase relations, Stratification

This review summarizes the knowledge ofMars’ interior structure, its inferred composition, and the anticipated seismological properties arising from its composition with particularfocus on Mars’ core. The emphasis on the corestems from the unusual morphology of the liquidus diagram of iron at moderate pressureswhen enriched in sulfur. From a fairly detailed
liquidus diagram constructed from experimental
studies, I identify a set of processes that could
act within Mars’ core: an iron “snow” from thecore-mantle boundary’s surface and a Fe3-xS2“ground fog” forming at the base of the core.
Depending on temperature and bulk sulfur
composition, these could form an inner core or
could stratify the outer core by enriching it insulfur, or both. Core stratification could be one
explanation for the extinction of Mars’ magnetic
field early in the planet’s history, and I demon-

Comparison of sizes and interior features of Earth and Mars. Mars is

strate the feasibility of this mechanism. The

almost a half-size scale model of the Earth, except for its thicker crust

crystallization processes in the core could beobservable in the seismic data that the future(Rivoldini et al., 2011) and its probable absence of an inner core. Core,Fe-FeS phase relations, Stratification

Mars geophysical mission, InSight, is planned
to provide. The core size, the presence of an inner core, and the wavespeed profile of the outer core, whose radialderivative provides a proxy for changes in composition, are key observables to seek.

Published: 2017/9/6
https://doi.org/10.1186/s40645-017-0139-4― 22 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Extreme geomagnetically induced currents
Kataoka R, Ngwira C[Keywords] Geomagnetically induced currents, Magnetic storms, Auroral substorms, Sudden commencements, Solarenergetic particles

We propose an emergency alert frameworkfor geomagnetically induced currents (GICs),
based on the empirically extreme values andtheoretical upper limits of the solar wind parameters and of dB/dt, the time derivative of magnetic field variations at ground. We expect thisframework to be useful for preparing against
extreme events. Our analysis is based on areview of various papers, including those presented during Extreme Space Weather Workshops held in Japan in 2011, 2012, 2013, and2014. Large-amplitude dB/dt values are themajor cause of hazards associated with threedifferent types of GICs: (1) slow dB/dt with ring
current evolution (RC-type), (2) fast dB/dt associated with auroral electrojet activity (AE-type),

Emergency alert framework for geomagnetically induced currents. The
equatorward boundary of the auroral oval according to the model of
Yokoyama et al. (1998) is shown by the solid curve, and the dotted curveand (3) transient dB/dt of sudden commence-shows its theoretical extrapolation. It is important to update the possible

ments (SC-type). We set “caution,” “warning,”

extension of the auroral oval toward middle to low latitudes during extremeand “emergency” alert levels during the main

magnetic storms.

phase of superstorms with the peak Dst index ofless than −300 nT (once per 10 years), −600 nT (once per 60 years), or −900 nT (once per 100 years), respectively.
The extreme dB/dt values of the AE-type GICs are 2000, 4000, and 6000 nT/min at caution, warning, and emergency
levels, respectively. For the SC-type GICs, a “transient alert” is also proposed for dB/dt values of 40 nT/s at low latitudes and 110 nT/s at high latitudes, especially when the solar energetic particle flux is unusually high.

Published: 2016/8/19
https://doi.org/10.1186/s40645-016-0101-x― 23 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Magnetohydrodynamics Modeling of Coronal Magnetic Field and Solar Eruptions Based on the
Photospheric Magnetic Field
Inoue S
[Keywords] Sun; Magnetic Field, Photosphere, Corona, Magnetohydrodynamics (MHD), Solar Active Region, Solar
Flare, Coronal Mass Ejection (CME)

In this paper, we summarize current progress on using the observed magnetic fields formagnetohydrodynamics (MHD) modeling of
the coronal magnetic field and of solar eruptions, including solar flares and coronal massejections (CMEs). Unfortunately, even with theexisting state-of-the-art solar physics satellites,
only the photospheric magnetic field can bemeasured. We first review the 3D extrapolationof the coronal magnetic fields from measurements of the photospheric field. Specifically, we
focus on the nonlinear force-free field (NLFFF)
approximation extrapolated from the three components of the photospheric magnetic field.
On the other hand, because in the force-free
approximation the NLFFF is reconstructed forThree-dimensional dynamics of the flux tube during an X2.2-class flareequilibrium states, the onset and dynamics ofobtained from our MHD simulation; the field lines with more (less) thansolar flares and CMEs cannot be obtained fromone-turn at t=0 are depicted in orange (blue). The Bz distribution is shownthese calculations. Recently, MHD simulations
using the NLFFF as an initial condition havebeen proposed for understanding these dynam-

in red and blue. The inset at t=0 shows the top view of the field lines; thenumber of field lines with less than one turn has been reduced. Eventually,
the large highly twisted flux tube is formed through the magnetic reconnection between these twisted liens.

ics in a more realistic scenario. These results
have begun to reveal complex dynamics, some of which have not been inferred from previous simulations of hypothetical situations, and they have also successfully reproduced some observed phenomena. Although MHD simulations
play a vital role in explaining a number of observed phenomena, there still remains much to be understood. Herein,
we review the results obtained by state-of-the-art MHD modeling combined with the NLFFF.

Published: 2016/7/4
https://doi.org/10.1186/s40645-016-0084-7― 24 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

MF and HF radar techniques for investigating the dynamics and structure of the 50 to 110 km
height region: a review
Reid I M[Keywords] Medium-frequency radar techniques, High-frequency radar techniques, Partial reflection radar, Spaced
antenna technique, Full correlation analysis, Mesosphere lower thermosphere region, D region, MLT region dynamics,
Meteor radar, Imaging Doppler interferometer

The application of medium-frequency (MF)and high-frequency (HF) partial reflection radar
to investigate the neutral upper atmosphereis one of the oldest such techniques still regularly in use. The techniques have been continuously improved and remain a robust andreliable method of obtaining wind velocities,
turbulence intensities, electron densities, andmeasurements of atmospheric structure in themesosphere lower thermosphere (MLT) region

MF and HF radars used to measure the MLT region. Green indicates(50 to 110 km). In this paper, we review recent

retired radars, blue current radars, and yellow dynasondes that have oper-

developments, discuss the strengths and weak-ated as IDI radars. See text and Tables 2 and 3 for further details.

nesses of the technique, and consider possible
improvements.

Published: 2015/10/19
https://doi.org/10.1186/s40645-015-0060-7― 25 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Advancing the understanding of the Sun-Earth interaction - the Climate and Weather of the SunEarth System (CAWSES) II Program
Tsuda T, Shepherd M G, Gopalswamy N[Keywords] Coupled solar–terrestrial system, Solar activity, Space weather, Geospace, Atmospheric coupling, Trends,
Global warming, Paleoclimatology

The Scientific Committee on Solar–Terrestrial Physics (SCOSTEP) of the International
Council for Science (ICSU) implemented aninternational collaborative program called Climate and Weather of the Sun–Earth System(CAWSES), which was active from 2004 to
2008; this was followed by the CAWSES II
program during the period of 2009–2013. The
CAWSES program was aimed at improving theunderstanding of the coupled solar–terrestrial
system, with special emphasis placed on the
short-term (weather) and long-term (climate)variability of solar activities and their effects on

A schematic concept of CAWSES II with four task groups (TGs), E-scienceand responses of Geospace and Earth’s envi-

and capacity building.

ronment. Following the successful implementation of CAWSES, the CAWSES II program pursued four fundamental questions addressing the way in which thecoupled Sun–Earth system operates over time scales ranging from minutes to millennia, namely, (1) What are thesolar influences on the Earth’s climate? (2) How will Geospace respond to an altered climate? (3) How does shortterm solar variability affect the Geospace environment? and (4) What is the Geospace response to variable inputs
from the lower atmosphere? In addition to these four major tasks, the SCOSTEP and CAWSES promoted E-scienceand informatics activities including the creation of scientific databases and their effective utilization in solar–terrestrial
physics research. Capacity building activities were also enhanced during CAWSES II, and this represented an important contribution of SCOSTEP to the world’s solar–terrestrial physics community. This introductory paper provides an
overview of CAWSES II activities and serves as a preface to the dedicated review papers summarizing the achievements of the program’s four task groups (TGs) and the E-science component.

Published: 2015/9/17
https://doi.org/10.1186/s40645-015-0059-0― 26 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

The science case for the EISCAT_3D radar
McCrea I, Aikio A, Alfonsi L, Belova E, Buchert S, Clilverd M, Engler N, Gustavsson B, Heinselman C, KeroJ, Kosch M, Lamy H, Leyser T, Ogawa Y, Oksavik K, Pellinen-Wannberg A, Pitout F, Rapp M, Stanislawska
I, Vierinen J[Keywords] EISCAT, EISCAT_3D, Radar, Incoherent scatter, Atmospheric science, Space physics, Plasma physics,
Solar system research, Space weather, Radar techniques

The EISCAT (European Incoherent SCATer)
Scientific Association has provided versatileincoherent scatter (IS) radar facilities on themainland of northern Scandinavia (the EISCAT
UHF and VHF radar systems) and on Svalbard(the electronically scanning radar ESR (EISCAT
Svalbard Radar) for studies of the high-latitude
ionised upper atmosphere (the ionosphere).
The mainland radars were constructed about
30 years ago, based on technological solutions

Schematic representation showing the volumetric imaging of an ionospheric layer above Scandinavia by EISCAT_3D. (Image courtesy of EISCAT Scientific Association)of that time. The science drivers of today, however, require a more flexible instrument, which allows measurements to be made from the troposphere to the topside
ionosphere and gives the measured parameters in three dimensions, not just along a single radar beam. The possibility
for continuous operation is also an essential feature. To facilitate future science work with a world-leading IS radar
facility, planning of a new radar system started first with an EU-funded Design Study (2005–2009) and has continued
with a follow-up EU FP7 EISCAT_3D Preparatory Phase project (2010–2014). The radar facility will be realised byusing phased arrays, and a key aspect is the use of advanced software and data processing techniques. This type ofsoftware radar will act as a pathfinder for other facilities worldwide. The new radar facility will enable the EISCAT_3D
science community to address new, significant science questions as well as to serve society, which is increasingly
dependent on space-based technology and issues related to space weather. The location of the radar within theauroral oval and at the edge of the stratospheric polar vortex is also ideal for studies of the long-term variability inthe atmosphere and global change. This paper is a summary of the EISCAT_3D science case, which was preparedas part of the EU-funded Preparatory Phase project for the new facility. Three science working groups, drawn fromthe EISCAT user community, participated in preparing this document. In addition to these working group members,
who are listed as authors, thanks are due to many others in the EISCAT scientific community for useful contributions,discussions, and support.

Published: 2015/7/29
https://doi.org/10.1186/s40645-015-0051-8― 27 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Short-term variability of the Sun-Earth system: an overview of progress made during the
CAWSES-II period
Gopalswamy N, Tsurutani B, Yihua Y[Keywords] Solar activity, Space weather, Coronal mass ejections, Flares, Solar energetic particle events, Geospace
impact, Geomagnetic storms

This paper presents an overview of results
obtained during the CAWSES-II period on
the short-term variability of the Sun and how
it affects the near-Earth space environment.
CAWSES-II was planned to examine the behavior of the solar-terrestrial system as the solar
activity climbed to its maximum phase in solar
cycle 24. After a deep minimum following cycle
23, the Sun climbed to a very weak maximum
in terms of the sunspot number in cycle 24(MiniMax24), so many of the results presented
here refer to this weak activity in comparison
with cycle 23. The short-term variability that has
immediate consequence to Earth and geospace
manifests as solar eruptions from closed-fieldregions and high-speed streams from coronalholes. Both electromagnetic (flares) and mass

Speed vs. width distributions of limb CMEs from cycles 23 and 24. Bothcycles show a good correlation between speed and width, but the slopes
are very different. The correlations coefficients (r) and the regression lines

emissions (coronal mass ejections - CMEs)

are given on the plot. Student’s t-test confirms that the slope difference

are involved in solar eruptions, while coronalis statistically significant. The data points at width=360o are halo CMEs,

holes result in high-speed streams that collide

which are mostly from cycle 24.

with slow wind forming the so-called corotatinginteraction regions (CIRs). Fast CMEs affect Earth via leading shocks accelerating energetic particles and creatinglarge geomagnetic storms. CIRs and their trailing high-speed streams (HSSs), on the other hand, are responsible forrecurrent small geomagnetic storms and extended days of auroral zone activity, respectively. The latter leads to theacceleration of relativistic magnetospheric ‘killer’ electrons. One of the major consequences of the weak solar activity
is the altered physical state of the heliosphere that has serious implications for the shock-driving and storm-causing
properties of CMEs. Finally, a discussion is presented on extreme space weather events prompted by the 23 July 2012super storm event that occurred on the backside of the Sun. Many of these studies were enabled by the simultaneous
availability of remote sensing and in situ observations from multiple vantage points with respect to the Sun-Earth line.

Published: 2015/6/17
https://doi.org/10.1186/s40645-015-0043-8― 28 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

eScience and Informatics for International Science Programs
Fox P, Kozyra J[Keywords] eScience, Informatics, Virtual observatory, Virtual organization, Collaboration, Interdisciplinary research

Both eScience and Informatics, their conceptual approaches, methods, and extant technicalsolutions, are still relatively new approaches inmany science fields. Collectively, they intend
to facilitate the electronic conduct of science(eScience) and the application of foundational
principles drawn from experience in a numberof fields of Informatics (e.g., helioinformatics,
geoinformatics, and climateinformatics). The
Climate and Weather of the Sun-Earth System
II (CAWSES II) eScience and Informatics effort
had the goal of promoting an international virtual institute and several virtual observatories inorder to advance system-level science investigations aligned with the four CAWSES II Task
Groups. This contribution elaborates on the key
elements of eScience and Informatics applicable to CAWSES II as a virtual organization in the

CAWSES II program concept for virtual institute for collaborative knowl-

context of the current science-data landscape.

edge development

We examine what was adopted for CAWSESII and highlight the successes and challenges of the effort. Based on the lessons learned from this effort and otherinternational communities, we present opportunities going forward that are relevant to both smaller collaborations andsuccessor large-scale programs (such as the Variability of the Sun and Its Terrestrial Impact (VarSITI)) that are being
recognized more as networks of science facilitated by a variety of modern information technologies.

Published: 2015/5/19
https://doi.org/10.1186/s40645-015-0042-9― 29 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

What is the solar influence on climate? Overview of activities during CAWSES-II
Seppälä A, Matthes K, Randall C E, Mironova I A[Keywords] Climate, Atmosphere, Solar irradiance, Total solar irradiance, TSI, Solar spectral irradiance, SSI, Energetic
particles, EPP, Cosmic rays

This paper presents an overview of the main
advances in the Key Questions identified by
the Task Group ‘What is the Solar Influenceon Climate’ by the SCOSTEP CAWSES-II science program. We go through different aspectsof solar forcing from solar irradiance, including
total solar irradiance (TSI) and solar spectral
irradiance (SSI), to energetic particle forcing,including energetic particle precipitation (EPP)
and cosmic rays (CR). Besides discussing themain advances in the timeframe 2009 to 2013,
we also illustrate the proposed mechanism forclimate variability for the different solar variability sources listed above. The key questions are
as follows: What is the importance of spectral
variations to solar influences on climate? Whatis the effect of energetic particle forcing on the

Energetic particle precipitation (EPP) impact on the atmosphere. Main
direct and indirect impacts from EPP (including EEP and SPE). EPP ionisation is focused on the polar regions leading to production of HOx andNOx shown in the figure. Transport processes are shown with grey dottedwhole atmosphere and what are the implica-

lines, while coupling mechanisms are indicated with grey dashed lines.

tions for climate? How well do models repro-

Direct chemical impacts are shown with black arrows.

duce and predict solar irradiance and energetic
particle influences on the atmosphere and climate?

Published: 2014/11/26
https://doi.org/10.1186/s40645-014-0024-3― 30 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Response of the mesosphere-thermosphere-ionosphere system to global change – CAWSES-II
contribution
Laštovička J, Beig G, Marsh D R[Keywords] Mesosphere, Thermosphere, Ionosphere, Long-term trends, Climatic change

Long-term trends in the mesosphere, thermosphere, and ionosphere are areas of researchof increasing importance both because they
are sensitive indicators of climatic change andbecause they affect satellite-based technologies which are increasingly important to modern life. Their study was an important part of
CAWSES-II project, as they were a topic of Task
Group 2 (TG-2) ‘How Will Geospace Respondto Changing Climate’. Three individual projectsof TG-2 were focused on important problems
in trend investigations. Significant progress wasreached in several areas such as understandingand quantifying the role of stratospheric ozone
changes in trends in the upper atmosphere,reaching reasonable agreement between
observed and simulated trends in mesospherictemperatures and polar mesospheric clouds, orunderstanding of why the thermospheric density trends are much stronger under solar cycle

Trends in the Earth’s atmosphere. The atmospheric layers are defined by
the temperature profile. The ionospheric layers are defined by the elec-

minimum conditions. The TG-2 progress thattron density profile (midnight at equator). Arrows indicate the direction ofis reviewed in this paper together with somechange. Red - warming, blue - cooling, green - no change of temperature,

results reached outside CAWSES-II so as toblack - changes in electron density (horizontal) and heights of ionospheric

have the full context of progress in trends inlayers (vertical).

the upper atmosphere and ionosphere.

Published: 2014/11/11
https://doi.org/10.1186/s40645-014-0021-6― 31 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Space and planetary sciences

The geospace response to variable inputs from the lower atmosphere: A review of the progress
made by Task Group 4 of CAWSES-II
Oberheide J, Kazuo S, Gurubaran S, Ward W E, Fujiwara H, Kosch M J, Makela J J, Takahashi H[Keywords] Geospace, Thermosphere, Ionosphere, Tides, Planetary waves, Gravity waves, Traveling ionosphericdisturbances, Traveling atmospheric disturbances

The advent of new satellite missions, groundbased instrumentation networks, and the development of whole atmosphere models over the
past decade resulted in a paradigm shift inunderstanding the variability of geospace, thatis, the region of the atmosphere between thestratosphere and several thousand kilometers above ground where atmosphere-ionosphere-magnetosphere interactions occur. It
has now been realized that conditions in geospace are linked strongly to terrestrial weather
and climate below, contradicting previous textbook knowledge that the space weather ofEarth’s near space environment is driven by

Sketch of meteorological impacts on geospace due to non-Sun-synchro-energy injections at high latitudes connectednous (nonmigrating) tides as observed by different satellites in various

with magnetosphere-ionosphere coupling andneutral and plasma parameters. The COSMIC figure is adapted withsolar radiation variation at extreme ultraviolet
wavelengths alone. The primary mechanism

permission from Lin et al. (2007), the IMAGE figure is adapted withpermission from Immel et al. (2006), the TIMED figure uses data from
Oberheide et al. (2006), and the SNOE figure is adapted with permission

through which energy and momentum are trans-

from Oberheide and Forbes (2008). Deep convective cloud data are fromferred from the lower atmosphere is throughthe ISCCP climatology. CHAMP neutral density data are provided by Dr

the generation, propagation, and dissipation of

X. Zhang and Dr. S. L. Bruinsma.

atmospheric waves over a wide range of spatial
and temporal scales including electrodynamic coupling through dynamo processes and plasma bubble seeding. The
main task of Task Group 4 of SCOSTEP’s CAWSES-II program, 2009 to 2013, was to study the geospace response
to waves generated by meteorological events, their interaction with the mean flow, and their impact on the ionosphereand their relation to competing thermospheric disturbances generated by energy inputs from above, such as auroral
processes at high latitudes. This paper reviews the progress made during the CAWSES-II time period, emphasizing
the role of gravity waves, planetary waves and tides, and their ionospheric impacts. Specific campaign contributions
from Task Group 4 are highlighted, and future research directions are discussed.

Published: 2014/2/11
https://doi.org/10.1186/s40645-014-0031-4― 32 ―

Review
Atmospheric and hydrospheric sciences

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Recent global nonhydrostatic modeling approach without using a cumulus parameterization tounderstand the mechanisms underlying cloud changes due to global warming
Akira T. Noda, Tomoki Ohno, Chihiro Kodama, Ying-Wen Chen, Naomi Kuba, Tatsuya Seiki, Yohei Yamada,
Masaki Satoh[Keywords] Clouds, Global nonhydrostatic model, Global warming, High-resolution climate simulation, Model
improvement

Clouds are the primary source of uncertainty
in the prediction of climate change. To reduce
the uncertainty of cloud simulations and overcome this difficulty in prediction, many climate
modeling centers are now developing a new
type of climate model, the global nonhydrostatic
atmospheric model, which reduces the uncertainty arising from a cumulus parameterizationby computing clouds explicitly using a cloud microphysics scheme. Among the global nonhydrostatic atmosphericmodels used in recent intercomparison studies, NICAM aims to project climate change by improving our understandingof cloud changes due to warming and related physical processes. NICAM is the first global nonhydrostatic model andwas developed by our research team. This review summarizes the outcomes of a recent major five-year research
program in Japan for studying climate using NICAM, as well as providing an overview of current issues regarding theuse of global kilometer-scale simulations in high-resolution climate modeling.

Published: 2023/8/18
https://doi.org/10.1186/s40645-023-00583-x― 34 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Greenhouse gases observing satellite 2 (GOSAT-2): Mission overview
Imasu R, Matsunaga T, Nakajima M, Yoshida Y, Shiomi K, Morino I, Saitoh N, Niwa Y, Someya Y, Oishi Y,
Hashimoto M, Noda H, Hikosaka K, Uchino O, Maksyutov S, Takagi H, Ishida H, Nakajima TY, Nakajima T,
Shi C[Keywords] GOSAT-2, GOSAT, Carbon dioxide, Methane, Carbon monoxide, Black carbon, Solar-induced, chlorophyll
fluorescence, TANSO-FTS-2, TANSO-CAI-2, Intelligent pointing mechanism

The Greenhouse gases Observing SATellite 2(GOSAT-2) was launched in October 2018 asa successor to GOSAT (launched in 2009),
the first satellite to specialize in greenhousegas observations. Compared to the GOSAT
sensors, the sensors of GOSAT-2 offer higher
performance in most respects. The quality andquantity of data from observations are expected
to be improved accordingly. The signal-to-noise
ratio (SNR) is better in both the SWIR and TIR
bands of TANSO-FTS-2, which is the main sensor of GOSAT-2. This improvement ultimately

Artistic image of GOSAT-2 in orbit (left-top), schematic image of the TAN-

enhances the accuracy of greenhouse gas

SO-FTS-2 sensor (left-bottom). Examples of observed column-averaged

concentration analysis. Furthermore, because

dry-air mole fraction products of CO2 (right-top), CH4 (right-middle), andof the improved SNR in the SWIR band, theCO (right-bottom). Values are averaged in each 2.5° mesh area for Marchnorthern limit at which data are obtainable in2019.

high-latitude regions of the Northern Hemisphere in winter, where observation data have remained unavailable because of weak signal strength, has moved tohigher latitudes. As better data are obtained in greater quantities, progress in carbon cycle research for high-latitude
regions is anticipated. Moreover, the improvement of SNR in the TIR band is expected to be considerable. Particularly,
the resolutions of the vertical concentration distributions of CO2 and CH4 have been improved drastically. The firstfunction introduced for GOSAT-2 that is not in GOSAT is an intelligent pointing mechanism: a cloud area avoidance
function using the in-field camera of TANSO-FTS-2. This function can increase the amounts of observation data globally and can improve the accuracy of CO2 emissions estimation and measurements of uptake intensity. The effects
are expected to be strong, especially for the tropics because cumulus clouds are the most common cloud type. The
intelligent pointing system can avoid the clouds effectively. Another important benefit of TANSO-FTS-2 is that the
wavelength range of Band 3 of SWIR has been expanded for measuring carbon monoxide (CO). Because CO originates from combustion, it is used to evaluate some effects of human activities in urban areas and biomass burning infields. Particularly, black carbon-type aerosols can be measured by the sub-sensor, TANSO-CAI-2, to assess biomassburning along with CO2 and CO by TANSO-FTS-2.

Published: 2023/7/3
https://doi.org/10.1186/s40645-023-00562-2― 35 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Climate-relevant properties of black carbon aerosols revealed by in situ measurements: a review
Nobuhiro Moteki[Keywords] Atmospheric chemistry, Atmospheric radiation, Climate, Aerosol, Light-absorbing aerosols, Black carbon

Light-absorbing aerosols affect atmosphericradiation, dynamics, and precipitations throughshortwave absorption in the atmosphere andsnowpack. Black carbon (BC) is considered themost significant contributor to global shortwave
absorption among all the known light-absorbing
aerosol components. In analyses and predictions of BC’s lifecycle and climate effects, multiscale field observations are needed to test thefundamental assumptions in the climate model.
In situ measurements, the focus of this review,
fill the gap of observational information acces-

Figure 1. Roles and relationships of the four-different approaches in aerosol-climate research. Laboratory analyses of collected samples, in-situ

sible from remote sensing and laboratory analy-

measurements, and remote sensing provide complementary observational

ses. This article reviews historical backgrounds,

information needed for reducing assumptions in the atmospheric chemical

recent advances in in situ measurements of BC,

transport model (sub-module of the climate model).

and the resulting observational findings used to
update the assumptions in climate models and remote sensing. Finally, we raise open problems that demand arethinking and future investigation.
Illustrating the physical principle of detecting the light-absorbing black carbon and iron oxidesaerosol particles using
the single-particle laser-induced incandescence

Published: 2023/3/6
https://doi.org/10.1186/s40645-023-00544-4― 36 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

The response of the hydrological cycle to temperature changes in recent and distant climatic
history
Shailendra Pratap, Yannis Markonis[Keywords] Global water cycle, Paleoclimate, Hydrological cycle, Water cycle intensification, Hydroclimatic variability

The relationship between the hydrologicalcycle and the temperature is rather complex
and of great importance to human socioeconomic activities. The prevailing theory suggeststhat as temperature increases the hydrologicalcycle is intensified. Practically, this means more
and heavier precipitation. However, the exact
magnitude of hydrological cycle response andits spatio-temporal characteristics is still underinvestigation. Looking back in Earth’s hydroclimatic history, it is easy to find some periods
where global temperature was substantially different than present. Here, we examine some ofthese periods to present the current knowledge about past hydrological cycle variability (specifically precipitation), andits relationship to temperature. The periods under investigation are the Mid-Miocene Climate Optimum, the EemianInterglacial Stage, the Last Glacial Maximum, the Heinrich and Dansgaard–Oeschger Events, the Bølling–Allerød, theYounger Dryas, the 8.2 ka event, the Medieval Climate Anomaly, and the Little Ice Age. We report that the hypothesisthat a warmer climate is a wetter climate could be an oversimplification, because the response of water cycle appears
to be spatio-temporally heterogeneous.

Published: 2022/5/31
https://doi.org/10.1186/s40645-022-00489-0― 37 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Marine microplastics as vectors of major ocean pollutants and its hazards to the marine ecosystem and humans
Tan Suet May Amelia, Wan Mohd Afiq Wan Mohd Khalik, Meng Chuan Ong, Yi Ta Shao, Hui-Juan Pan,
Kesaven Bhubalan[Keywords] Adsorption, Bioaccumulation, Contaminant, Microplastic, Pollutant, Vector

Microplastic pollutes water, land, air, andgroundwater environments not only visually
but also ecologically for plants, animals, andhumans. Microplastic has been reported toact as vectors by sorbing pollutants and contributing to the bioaccumulation of pollutants,
particularly in marine ecosystems, organisms,
and subsequently food webs. The inevitable exposure of microplastic to humans emphasises the need to review thepotential effects, exposure pathways, and toxicity of microplastic toward human health. Therefore, this review wasaimed to reveal the risks of pollutant sorption and bioaccumulation by microplastic toward humans, as well as thedominant types of pollutants sorbed by microplastic, and the types of pollutants that are bioaccumulated by microplastic
in the living organisms of the marine ecosystem. The possible factors influencing the sorption and bioaccumulationof pollutants by microplastic in marine ecosystems were also reviewed. The review also revealed the prevailing typesof microplastic, abundance of microplastic, and geographical distribution of microplastic in the aquatic environment
globally. The literature review revealed that microplastic characteristics, chemical interactions, and water properties
played a role in the sorption of pollutants by microplastic. The evidence of microplastic posing a direct medical threat
to humans is still lacking albeit substantial literature has reported the health hazards of microplastic-associated monomers, additives, and pollutants. This review recommends future research on the existing knowledge gaps in microplastic research, which include the toxicity of microplastic, particularly to humans, as well as the factors influencing
the sorption and bioaccumulation of pollutants by microplastic.

Published: 2021/1/22
https://doi.org/10.1186/s40645-020-00405-4― 38 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Applications of soft computing models for predicting sea surface temperature: a comprehensive
review and assessment
Masoud Haghbin, Ahmad Sharafati, Davide Motta, Nadhir Al-Ansari, Mohamadreza Hosseinian Moghadam
Noghani[Keywords] Soft computing, Sea Surface Temperature, Prediction

The application of soft computing (SC) models
for predicting environmental variables is widely
gaining popularity, because of their capability
to describe complex non-linear processes. The
sea surface temperature (SST) is a key quantity in the analysis of sea and ocean systems,
due to its relation with water quality, organisms,
and hydrological events such as droughts andfloods. This paper provides a comprehensive
review of the SC model applications for estimating SST over the last two decades. Types of model (based on artificial neural networks, fuzzy logic, or other SC
techniques), input variables, data sources, and performance indices are discussed. Existing trends of research in thisfield are identified, and possible directions for future investigation are suggested.

Published: 2021/1/5
https://doi.org/10.1186/s40645-020-00400-9― 39 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Two decades of Earth system modeling with an emphasis on Model for Interdisciplinary
Research on Climate (MIROC)
Michio Kawamiya, Tomohiro Hajima, Kaoru Tachiiri, Shingo Watanabe, Tokuta Yokohata[Keywords] Earth system model, Climate change, IPCC, Carbon cycle, Biogeochemistry, Interdisciplinary project,
Remaining carbon budget, Socioeconomics, Nitrogen, Iron.

The past 20 years of research using Earthsystem models (ESMs) is reviewed with anemphasis on results from the ESM based on
MIROC (Model for Interdisciplinary Researchon Climate) developed in Japan. Earth system models are climate models incorporating
biogeochemical processes such as the carbon
cycle. The development of ESM was triggered bystudies of the feedback between climate change
and the carbon cycle. State-of-the-art ESMs aremuch more realistic than the first ESMs. They
now include various biogeochemical processes
other than carbon, such as atmospheric chemistry and the nitrogen and iron cycles as wellas nutrient transport by atmospheric dust andrivers. They are used to address many prac-

Conceptual diagram of Earth system model (ESM) projections oftical issues, such as evaluating the amount of

global change: Anthropogenic greenhouse gas emissions and nitrogencarbon dioxide emissions that is consistent with

fixation are increasing; ESMs can model interactions between climate

climate change mitigation targets, and are indis-change and biogeochemical cycles.

pensable tools for the development of climatechange mitigation policies. Novel, ambitious attempts to use ESMs include coupling socioeconomics with Earth systems, and projecting the carbon cycle on decadal timescales. Development of ESMs requires ongoing integration ofmultiple aspects of climate science. Emerging applications of ESMs can bring forth meaningful insights, and should
be directed toward expanding connections with fields outside climate science, e.g., socioeconomics.

Published: 2020/10/20
https://doi.org/10.1186/s40645-020-00369-5― 40 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

d4PDF: large-ensemble and high-resolution climate simulations for global warming risk assessment
Masayoshi Ishii, Nobuhito Mori
[Keywords] Global warming, d4PDF, ensemble climate simulation, atmospheric model, dynamical downscaling,detection and attribution, impact assessment, climate change adaptation, natural hazard, storm surge

A large-ensemble climate simulation database, which is known as the database for policy decision-making for future climate changes(d4PDF), was designed for climate change risk
assessments. Since the completion of the first
set of climate simulations in 2015, the databasehas been growing continuously. It contains theresults of ensemble simulations conducted
over a total of thousands years respectively forpast and future climates using high-resolution
global (60 km horizontal mesh) and regional(20 km mesh) atmospheric models. Several
sets of future climate simulations are available,
in which global mean surface air temperatures
are forced to be higher by 4 K, 2 K, and 1.5 K
relative to preindustrial levels. Nonwarming past
climate simulations are incorporated in d4PDF
along with the past climate simulations. The
total data volume is approximately 2 petabytes.

Time series of global mean surface air temperature anomalies of d4PDF

The atmospheric models satisfactorily simulate

for past (light blue), nonwaming (blue), +1.5 K (green), +2 K (orange), andthe past climate in terms of climatology, natural+4 K (red) climate simulations and CMIP5 historical and RCP8.5 experi-

variations, and extreme events such as heavy
precipitation and tropical cyclones. In addition,
data users can obtain statistically significant

ments with six climate models. Shading indicates two-sigma uncertainties.
Time series are drawn relative to the averages for the period from 1975
to 2005.

changes in mean states or weather and climate extremes of interest between the past and future climates via a
simple arithmetic computation without any statistical assumptions. The database is helpful in understanding futurechanges in climate states and in attributing past climate events to global warming. Impact assessment studies forclimate changes have concurrently been performed in various research areas such as natural hazard, hydrology,
civil engineering, agriculture, health, and insurance. The database has now become essential for promoting climate
and risk assessment studies and for devising climate adaptation policies. Moreover, it has helped in establishing aninterdisciplinary research community on global warming across Japan.

Published: 2020/10/7
https://doi.org/10.1186/s40645-020-00367-7― 41 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

DYAMOND: The DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic
Domains
Stevens B, Satoh M, Auger L, Biercamp J, Bretherton CS, Chen X, Duben P, Judt F, Khairoutdinov M, Klocke
D, Kodama C, Kornblueh L, Lin SJ, Neumann P, Putman WM, Rober N, Shibuya R, Vanniere B, Vidale PL,
Wedi N, Zhou L[Keywords] Climate modelling, Model intercomparison project, Tropical Convection

A review of the experimental protocol andmotivation for DYAMOND, the first intercomparison project of global storm-resolving models,is presented. Nine models submitted simulation
output for a 40-day (1 August–10 September2016) intercomparison period. Eight of these
employed a tiling of the sphere that was uniformly less than 5 km. By resolving the transient
dynamics of convective storms in the tropics,
global storm-resolving models remove the needto parameterize tropical deep convection, providing a fundamentally more sound representation of the climate system and a more naturallink to commensurately high-resolution data

Snapshot of DYAMOND Models. Shown is a snapshot of the models takenfrom satellite-borne sensors. The models andfrom the perspective of the Himawari-8. The images are for the cloudsome basic characteristics of their output arescene on 4 August 2016, and are qualitatively rendered based on each

described in more detail, as is the availability

model’s condensate fields to illustrate the variety of convective structuresand planned use of this output for future sci-

resolved by the models, and difficulty of distinguishing them form actual

entific study. Tropically and zonally averaged

observations. From left to right, the images are from IFS-4km, IFS-9km,

energy budgets, precipitable water distributions,

NICAM, and SAM (top row); Arpege, Himawari, and ICON (middle row);
FV3, GEOS5, UKMO and MPAS (bottom row).

and precipitation from the model ensemble are
evaluated, as is their representation of tropical
cyclones and the predictability of column water vapor, the latter being important for tropical weather.

Published: 2019/9/30
https://doi.org/10.1186/s40645-019-0304-z― 42 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Toward reduction of the uncertainties in climate sensitivity due to cloud processes using a global
non-hydrostatic atmospheric model
Satoh M, Noda A, Seiki T, Chen Y, Kodama C, Yamada Y, Kuba N, Sato Y[Keywords] NICAM, Cloud microphysics scheme, Cloud changes, Cloud feedback, Global non-hydrostatic model,
Global warming

In estimates of climate sensitivity obtained
from global models, the need to represent
clouds introduces a great deal of uncertainty.
To address this issue, approaches using ahigh-resolution global non-hydrostatic model arepromising: the model captures cloud structureby explicitly simulating meso-scale convective
systems, and the results compare reasonably
well with satellite observations. We review theoutcomes of a 5-year project aimed at reducing the uncertainty in climate models due tocloud processes using a global non-hydrostatic
model. In our project, which was conducted asa subgroup of the Program for Risk Information
on Climate Change, or SOUSEI, we use the non-hydrostatic icosahedral atmospheric model (NICAM) to study cloud
processes related to climate change. NICAM performs numerical simulations with much higher resolution (about 7
km or 14 km mesh) than conventional global climate models (GCMs) using cloud microphysics schemes without acumulus parameterization scheme, which causes uncertainties in climate projection.
The subgroup had three research targets: analyzing cloud changes in global warming simulations with NICAM withthe time-slice approach, sensitivity of the results to the cloud microphysics scheme employed, and evaluating circulation changes due to global warming. The research project also implemented a double-moment bulk cloud microphysics
scheme and evaluated its results using satellite observation, as well as comparing it with a bin cloud microphysics
scheme. The future projection simulations show in general increase in high cloud coverage, contrary to results withother GCMs. Changes in cloud horizontal-size distribution size and structures of tropical/extratropical cyclones canbe discussed with high resolution simulations. At the conclusion of our review, we also describe the future prospectsof research for global warming using NICAM in the program that followed SOUSEI, known as TOUGOU.

Published: 2018/10/29
https://doi.org/10.1186/s40645-018-0226-1― 43 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Maritime continent coastlines controlling Earth’s climate
Yamanaka MD, Ogino SY, Wu PM, Hamada JI, Mori S, Matsumoto J, Syamsudin F[Keywords] Indonesian maritime continent, Atmosphere–ocean–land interaction, Convective clouds, Multiple scales,
Diurnal cycle, Sea−land breeze circulation

During the Monsoon Asian Hydro−Atmosphere Scientific Research and Prediction Initiative (MAHASRI; 2006–16), we carried out
two projects over the Indonesian maritime continent (IMC), constructing the Hydrometeorological Array for Intraseasonal Variation−Monsoon
Automonitoring (HARIMAU; 2005–10) radar
network and setting up a prototype institute for

Maritime-continental diurnal-cycle rain and latent heat controlling global

climate studies, the Maritime Continent Centerclimateof Excellence (MCCOE; 2009–14). Here, we
review the climatological features of the world’s largest “regional” rainfall over the IMC studied in these projects. The
fundamental mode of atmospheric variability over the IMC is the diurnal cycle generated along coastlines by land−seatemperature contrast: afternoon land becomes hotter than sea by clear-sky insolation before noon, with the opposite
contrast before sunrise caused by evening rainfall-induced “sprinkler”-like land cooling (different from the extratropicalinfrared cooling on clear nights). Thus, unlike the extratropics, the diurnal cycle over the IMC is more important in
the rainy season. The intraseasonal, seasonal to annual, and interannual climate variabilities appear as amplitude
modulations of the diurnal cycle. For example, in Jawa and Bali the rainy season is the southern hemispheric summer, because land heating in the clear morning and water vapor transport by afternoon sea breeze is strongest in
the season of maximum insolation. During El Niño, cooler sea water surrounding the IMC makes morning maritime
convection and rainfall weaker than normal. Because the diurnal cycle is almost the only mechanism generating
convective clouds systematically near the equator with little cyclone activity, the local annual rainfall amount in thetropics is a steeply decreasing function of coastal distance (e-folding scale 100–300 km), and regional annual rainfall
is an increasing function of “coastline density” (coastal length/land area) measured at a horizontal resolution of 100
km. The coastline density effect explains why rainfall and latent heating over the IMC are twice the global mean
for an area that makes up only 4% of the Earth’s surface. The diurnal cycles appearing almost synchronously over
the whole IMC generate teleconnections between the IMC convection and the global climate. Thus, high-resolution(<<100 km; <<1 day) observations and models over the IMC are essential to improve both local disaster prevention
and global climate prediction.

Published: 2018/4/4
https://doi.org/10.1186/s40645-018-0174-9― 44 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Outcomes and challenges of global high-resolution non-hydrostatic atmospheric simulations
using the K computer
Satoh M, Tomita H, Yashiro H, Kajikawa Y, Miyamoto Y, Yamaura T, Miyakawa T, Nakano M, Kodama C, Noda
A T, Nasuno T, Yamada Y, Fukutomi Y[Keywords] K computer, NICAM, intra-seasonal oscillations, Madden-Julian oscillation, tropical cyclone, global nonhydrostatic modelThis article reviews the major outcomes of a
5-year (2011–2016) project using the K computer to perform global numerical atmosphericsimulations based on the non-hydrostatic icosahedral atmospheric model (NICAM). The K
computer was made available to the public in
September 2012 and was used as a primaryresource for Japan’s Strategic Programs forInnovative Research (SPIRE), an initiative toinvestigate five strategic research areas; theNICAM project fell under the research area ofclimate and weather simulation sciences. Combining NICAM with high-performance computing
has created new opportunities in three areasof research: (1) higher resolution global simulations that produce more realistic representa-

Resolution dependencies of simulated cloud distribution: mesh size 14km, 3.5 km, and 870 m.

tions of convective systems, (2) multi-member
ensemble simulations that are able to perform extended-range forecasts 10–30 days in advance, and (3) multi-decadalsimulations for climatology and variability. Before the K computer era, NICAM was used to demonstrate realistic simulations of intra-seasonal oscillations including the Madden-Julian oscillation (MJO), merely as a case study approach.
Thanks to the big leap in computational performance of the K computer, we could greatly increase the number ofcases of MJO events for numerical simulations, in addition to integrating time and horizontal resolution. We conclude
that the high-resolution global non-hydrostatic model, as used in this five-year project, improves the ability to forecast
intra-seasonal oscillations and associated tropical cyclogenesis compared with that of the relatively coarser operationalmodels currently in use. The impacts of the sub-kilometer resolution simulation and the multi-decadal simulations
using NICAM are also reviewed.

Published: 2017/4/28
https://doi.org/10.1186/s40645-017-0127-8― 45 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

A review of atmospheric chemistry observation at mountain sites
Okamoto S, Tanimoto H[Keywords] Atmospheric observation, High-altitude station, Long-range transport, Seasonal cycle, Long-term trend,
Biomass burning, Anthropogenic pollution

Located far from anthropogenic emission
sources, high-altitude mountain stations are
considered to be ideal sites for monitoring climatic and environmentally important baselinechanges in free tropospheric trace gases andaerosols. In addition, the observations taken
at these stations are often used to study thelong-range transport of dust as well as anthropogenic and biomass burning pollutants fromsource regions and to evaluate the performanceof global and regional models. In this paper, wesummarize the results from past and ongoing
field measurements of atmospheric constituentsat high-altitude stations across the globe, withparticular emphasis on reactive trace species
including tropospheric ozone, along with its

Map showing the distribution of high-altitude mountain stations discussed

precursors such as carbon monoxide, nitrogenin this paper. Circles with abbreviations denote stations providing the dataoxides, total reactive nitrogen, and nonmeth-presented in this paper. ASK Assekrem, CHA Chiricahua NM, CMN Monteane hydrocarbons. Over the past decades,

Cimone, GRB Great Basin NP, HPO Mt. Happo, ISK Issyk-Kul, IZO Izãna,

our understanding of the temporal variability
and meteorological mechanisms of long-range
transport has advanced in tandem with prog-

JFJ Jungfraujoch, KVV Krvavec, LAV Lassen Volcanic NP, LLN Lulin, LQO
La Quiaca Observatorio, MBO Mt. Bachelor Observatory, MKN Mt. Kenya,
MDY Mondy, MLO Mauna Loa, NWR Niwot Ridge, PMO Pico Mountain
Observatory, PYR Nepal Climate Observatory–Pyramid, SNB Sonnblick,ress in instrumentation and modeling. Finally,

TAR Tanah Rata, WHI Whistler Mountain, WLG Mt. Waliguan, YEL Yel-the future needs of atmospheric chemistry

lowstone NP, YOS Yosemite NP, ZSF Zugspitze–Schneefernerhaus, ZUG

observations at mountain sites are addressed.

Zugspitze–Gipfel. Triangles with abbreviations denote stations for whichdata are not presented but are reviewed in this paper. ARO Arosa, FWS
Mt. Fuji, KSL Kislovodsk.

Published: 2016/10/26
https://doi.org/10.1186/s40645-016-0109-2― 46 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

A review of progress towards understanding the transient global mean surface temperature
response to radiative perturbation
Yoshimori M, Watanabe M, Shiogama H, Oka A, Abe-Ouchi A, Ohgaito R, Kamae Y[Keywords] Transient climate response, Equilibrium climate sensitivity, Climate feedback, Ocean heat uptake efficacy,
Efficacy of forcing

The correct understanding of the transient
response to external radiative perturbation isimportant for the interpretation of observed
climate change, the prediction of near-futureclimate change, and committed warming underclimate stabilization scenarios, as well as theestimation of equilibrium climate sensitivity
based on observation data. It has been known
for some time that the radiative damping rate
per unit of global mean surface temperature
increase varies with time, and this inconstancy
affects the transient response. Knowledge ofthe equilibrium response alone is insufficient,but understanding the transient response ofRelation between global mean surface air temperature and top-of-the-at-

the global mean surface temperature has mademosphere net radiation changes from the preindustrial control simulation

rapid progress. The recent progress accompa-

in the MIROC3.2 (medres) atmosphere-ocean general circulation model

nies the relatively new concept of the efficacies

experiments. Black crosses: 1pctCO2 experiment (every year for 1-140

of ocean heat uptake and forcing. The ocean
heat uptake efficacy associates the tempera-

years); blue crosses: abrutp4xCO2 experiment (every year for 1-150
years), red crosses: const4xCO2 experiment (every 20-year average for141-3680 years); blue line: linear regression for the 150-year abrupt4xCO2

ture response induced by ocean heat uptake

experiment; Blue circles: equilibrium temperature response to 4xCO2 esti-with equilibrium temperature response, and themated by Gregory’s method for 10 abrupt4xCO2 20-year-long ensemble

efficacy of forcing compares the temperature
response caused by non-CO2 forcing with thatexperiments (that start from different initial conditions in the preindustrial
control simulation).

by CO2 forcing.
In this review article, recent studies on these efficacies are discussed, starting from the classical global feedback
framework and basis of the transient response. An attempt is made to structure different studies that emphasize different aspects of the transient response and to stress the relevance of those individual studies. The implications on thedefinition and computation of forcing and on the estimation of the equilibrium response in climate models are also discussed. Along with these discussions, examples are provided with MIROC climate model multi-millennial simulations

Published: 2016/7/18
https://doi.org/10.1186/s40645-016-0096-3― 47 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Overview of the development of the Aerosol Loading Interface for Cloud microphysics In Simulation (ALICIS)
Iguchi T, Choi I-J, Sato Y, Suzuki K, Nakajima T[Keywords] Cloud microphysics, Cloud and aerosol, Regional modeling, Dynamical downscaling

This review summarizes the scientific background of and past/prospective update strategies for the development of the Aerosol Loading
Interface for Cloud microphysics In Simulation(ALICIS). ALICIS provides a novel approach forcoupling downscaled mesoscale cloud-resolving simulations to large-scale aerosol-transport
simulations. Realistic aerosol loading, including
spatio-temporal aerosol variations and particle-size spectra, is implemented in the cloud-resolving simulations. Prior studies employing

Conceptual diagram of the coupling framework between a large-scale

ALICIS have demonstrated how the interface

aerosol transport model and a regional-scale cloud resolving model using

introduction significantly improves the repro-

the ALICIS module.

ducibility of the simulated microphysical cloud
structure through better representation of aerosol effects on cloud.

Published: 2015/12/11
https://doi.org/10.1186/s40645-015-0075-0― 48 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

The dynamics of the mesosphere and lower thermosphere: a brief review
Vincent R A[Keywords] Atmospheric tides, Gravity waves, Planetary waves, Middle atmosphere, Mesosphere, Lower
thermosphere, Wave coupling

The dynamics of the mesosphere-lower thermosphere (MLT) (60 to 110 km) is dominated bywaves and their effects. The basic structure of
the MLT is determined by momentum deposition
by small-scale gravity waves, which drives asummer-to-winter pole circulation at the mesopause. Atmospheric tides are also an importantcomponent of the dynamics of the MLT. Observations from extended ground-based networks,
satellites as well as numerical modelling showthat non-migrating tidal modes in the MLT are
more important than previously thought, withevidence for directly coupling into the thermosphere/ionosphere. Major disturbances lower
in the atmosphere, such as wintertime sudden
stratospheric warmings, temporarily disrupt

The 2006 major sudden warming. Top: time-height cross-section of temperatures during the major SSW in late January 2006. Note the descentand disappearance of the stratopause at the peak of the warming and its

the circulation pattern and thermal structure ofsubsequent reappearance and descent from the mesosphere. Bottom:

the MLT. In the equatorial mesosphere, gravity

the time variation of the zonal-mean zonal wind at 10 hPa and 60 N. The

wave driving leads to oscillations in the zonal

blue line shows the wind during the stratwarm, while the red line depicts

wind on semiannual time scales, although

the climatalogical seasonal cycle. Adapted from Figure one of Yamazaki

variability on quasi-biennial time scales is also
apparent. Planetary-scale waves such as theet al. (2012).
Stratospheric warmings occur when large-scale planetary waves break inthe middle atmosphere (10-100 km) in winter. This figure shows that thequasi-two-day wave temporarily dominate thewhole middle atmosphere is affected, so that the EW (zonal) winds anddynamics of the summertime MLT, especially inthe temperature structure temporarily revert to summer-like conditions.

the southern hemisphere. Impacts may include

The zonal means winds in the stratosphere (blue line in bottom figure)short-term changes to the thermal structure

become westward (negative) for a short time while those above 70 km

and physics of the high-latitude MLT. Here, we(the mesosphere) become eastward. In turn, this change in the prevailingbriefly review the dynamics of the MLT, with aparticular emphasis on developments in thepast decade.

wind affects the vertical propagation of atmospheric gravity waves andchanges their impact on the middle atmosphere. The effects of stratospheric warmings can also be observed in the ionosphere, impacting onradiowave propagation.

Published: 2015/3/18
https://doi.org/10.1186/s40645-015-0035-8― 49 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Modeling in Earth system science up to and beyond IPCC AR5
Hajima T, Kawamiya M, Watanabe M, Kato E, Tachiiri K, Sugiyama M, Watanabe S, Okajima H, Ito A[Keywords] Earth system science, Earth system model, Carbon and nitrogen cycle, Land and ocean CO2 uptake,
Ocean acidification, Land-use and land-cover change, EMICs, Geoengineering, Iron deposition

Changes in the natural environment that are
the result of human activities are becoming evident. Since these changes are interrelated andcan not be investigated without interdisciplinary
collaboration between scientific fields, Earthsystem science (ESS) is required to provide
a framework for recognizing anew the Earthsystem as one composed of its interacting subsystems. The concept of ESS has been partially realized by Earth system models (ESMs).
In this paper, we focus on modeling in ESS,

Schematic diagram of Earth system models

review related findings mainly from the latest
assessment report of the Intergovernmental Panel on Climate Change, and introduce tasks under discussion for the
next phases of the following areas of science: the global nitrogen cycle, ocean acidification, land-use and land-coverchange, ESMs of intermediate complexity, climate geoengineering, ocean CO2 uptake, and deposition of bioavailable
iron in marine ecosystems. Since responding to global change is a pressing mission in Earth science, modeling willcontinue to contribute to the cooperative growth of diversifying disciplines and expanding ESS, because modelingconnects traditional disciplines through explicit interaction between them.

Published: 2014/12/18
https://doi.org/10.1186/s40645-014-0029-y― 50 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

The Non-hydrostatic Icosahedral Atmospheric Model: Description and Development
Satoh M, Tomita H, Yashiro H, Miura H, Kodama C, Seiki T, Noda A, Yamada Y, Goto D, Sawada M, Miyoshi
T, Niwa Y, Hara M, Ohno Y, Iga S, Arakawa T, Inoue T, Kubokawa H[Keywords] Global non, hydrostatic model, Icosahedral grid, Global cloud-resolving simulations

This article reviews the development of a
global non-hydrostatic model, focusing on thepioneering research of the Non-hydrostatic Icosahedral Atmospheric Model (NICAM). Veryhigh resolution global atmospheric circulation
simulations with horizontal mesh spacing ofapproximately O (km) were conducted using
recently developed supercomputers. Thesetypes of simulations were conducted with a
specifically designed atmospheric global model
based on a quasi-uniform grid mesh structure
and a non-hydrostatic equation system. This
review describes the development of each
dynamical and physical component of NICAM,
the assimilation strategy and its related models,and provides a scientific overview of NICAM
studies conducted to date.
Icosahedral grids for grid division levels of 3, 4, and 5 (from left to right)(horizontal mesh spacings of approximately 893, 446 and 223 km).
Cloud distribution simulated by the NICAM 870 m grid spacing experiment.

Published: 2014/10/14
https://doi.org/10.1186/s40645-014-0018-1― 51 ―

Review
Human geosciences
Biogeosciences

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Human geosciences

Geomorphological processes and their connectivity in hillslope, fluvial, and coastal areas in
Bangladesh: A review
B. M. Refat Faisal, Yuichi S. Hayakawa[Keywords] Ganges-Brahmaputra-Meghna (GBM), Bangladesh, Satellite remote sensing, Fluvial processes, Sediment
dispersal, Landslides, Coastal erosion

Geomorphological knowledge is critical inunderstanding watershed scale surface processes, including steep mountainous areas andflat lowlands, particularly if the mid- and downstream areas are densely populated and hazard
assessments are highly required. However, ourknowledge about such surface processes has
relatively been limited in some areas in South
Asia due likely to the lack of comprehensive
studies of geomorphology and related fields.
This article undertakes an overview of the geomorphological processes of the disaster-pronedeltaic landscape of the Ganges–Brahmaputra–
Meghna (GBM), particularly focusing on fluvial

An overview of geomorphic connectivity in the Ganges-Brahmaputra Basinprocesses. The area locates in the downstream

with a focus on Bangladesh in the downstream domainof the watershed system including Himalayan
Mountains and highly connected with the upper basin morphodynamics, hydrology, and sediment flux. The previous
studies are summarized at different geomorphic settings concerning hillslopes, fluvial plains, and coastal areas toprovide clarity about the geomorphic processes linking erosion-prone upstream source areas to deposition-dominateddownstream areas. The review found that most of the geomorphic researches in Bangladesh are exploring landslide
inventory and susceptibility mapping in hilly areas; river channel or riverbank shifting, riverbank erosion and accretionin fluvial environments; watershed morphometric analysis and geomorphic unit identification in plain land; and coastline shifting or coastal erosion and accretion in coastal environments at a small scale. Then, we discuss the fluvial
dynamics and sediment transport of the GBM river system to address the knowledge gap in the context of deltaic
plain land in Bangladesh, where upstream fluvial sedimentation processes impact the geomorphic connectivity from
Himalayan to the Bay of Bengal. Although some studies on the fluvial dynamics and sediment dispersal in the upstream
GBM river basin are present, the fluvial processes in the downstream domain of Bangladesh are not fully understoodwith a limited number of research with field-based approaches. Some future perspectives of geomorphic researchin Bangladesh are then mentioned to understand better the complex geomorphological settings in the entire GBM
watershed and to strengthen the existing research capacity. This review will also develop a holistic understanding offluvial geomorphic processes of the GBM River to the policymakers and may be helpful to improve the transboundary
river basin management policies or strategies.

Published: 2022/7/25
https://doi.org/10.1186/s40645-022-00500-8― 54 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Human geosciences

A Review of Theoretical Salt Weathering Studies for Stone Heritage
Oguchi, C. T., Swe Yu[Keywords] Salt weathering theories, Crystal growth pressure, Hydration, Thermal expansion of salt

Salt weathering can cause substantial deterioration of natural rocks, building stones, masonry materials, monuments, andengineering structures. Nearly two centuries of salt weatheringstudies, both theoretically and empirically, have manifested its
power as well as its complexity. This paper attempts to unite thekinds of literature assess the various theories in the light of the
combined information. The theoretical approaches concerning
the most cited mechanisms of salt weathering such as crystallization, hydration and thermal expansion of crystalline salts arethoroughly reviewed. It is understood that there is no universally
acceptable hard and sound theoretical information on this topic
yet. More precise theories should be developed to elucidate thecomplications of the mechanisms of salt weathering as well as
to interpret the results of empirical studies.

Example of a honeycomb structure at Giza, Egypt.

Published: 2021/5/7
https://doi.org/10.1186/s40645-021-00414-x― 55 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Human geosciences

Arsenic cycling in the Earth’s crust and hydrosphere: interaction between naturally occurring
arsenic and human activities
Masuda H[Keywords] Arsenic contamination, geologic cycle, plate tectonics, reduction, oxidation

Field-based research on naturally occurring
arsenic contamination of surface waters andgroundwaters and the mechanisms of contamination are reviewed. The distribution of arsenic
is strongly related to areas of active plate tectonics, magmatism and associated hydrothermal activity, and high rates of erosion. Sourcesof arsenic contamination are mainly hydrothermal water, sulfide and arsenide minerals, volcanic ash, and iron oxyhydroxide/oxide as weathering products. The promotion of the reduction
and oxidation of arsenic source minerals by insitu microbial activity is an important secondary
mechanism that often determines arsenic levels
in groundwater. Anthropogenic activities, suchas geothermal and mining operations, as well
as excess pumping of shallow groundwaters,
disperse arsenic in the environment, thereby

Geologic cycle concerning arsenic transportation in the geosphere andsurface of the Earth shows the arsenic recycles in association with active
tectonics.
Digit in parenthesis gives the average concentrations of each geologic
bpdy. Purple and blue colored letters indicate the releasing and fixing
mechanisms of arsenic in the cycle.

expanding areas of arsenic contamination.

Published: 2018/11/1
https://doi.org/10.1186/s40645-018-0224-3― 56 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Biogeosciences

Geological history of the land area between Okinawa Jima and Miyako Jima of the Ryukyu
Islands, Japan, and its phylogeographical significance for the terrestrial organisms of these andadjacent islands
Watanabe N, Arai K, Otsubo M, Toda M, Tominaga A, Chiyonobu S, Sato T, Ikeda T, Takahashi A, Ota H, Iryu Y[Keywords] Ryukyu Islands, Kerama gap, Okinawa–Miyako submarine plateau, Pleistocene, Shimajiri Group, Ryukyu
Group, Vertebrate, Phylogeography, OMSP hypothesis

The modern and Late Pleistocene terrestrial fauna of
Miyako Jima and adjacent islands (the Miyako Islands) in
the southern Ryukyu Islands, southwestern Japan, includes
some endemic taxa or genetically unique populations that
exclusively have closest allies in the more isolated Okinawa
Jima and adjacent islands (the Okinawa Islands) than in the
Yaeyama Islands, which are located southwest of the Miyako
Islands with much narrower intervening straits. Those taxa
or populations include representatives of lineages that havephysiologically highly limited ability for over-sea dispersal
and the Miyako Islands are currently separated from the
Okinawa Islands by at least 300 km of open water; therefore, the formation of this phylogeographical pattern is perplexing. In this study, we review the late Cenozoic geologyof the Miyako Islands, southern Okinawa Jima, the Okinawa–Miyako submarine plateau (OMSP; a plateau locatedbetween Okinawa Jima and Miyako Jima), and the Kerama
gap, which is a depression between the OMSP and OkiChanges in the paleogeography of the Okinawa–Miyako
nawa Jima. We then consider the origin of the modern andarea and migration of terrestrial vertebrates. 1. a Period
Late Pleistocene terrestrial animals, including a number offrom after deposition of the Shimajiri Group to before deponon-volant vertebrates on the Miyako Islands. Finally, we
sition of the Ryukyu Group (ca. 2 to 1.7–1.4 Ma). b Period
propose a new hypothesis (the OMSP hypothesis) to explainof interglacial highstands of sea level during deposition of
the enigmatic composition of modern and Late Pleistocene
the main body of the Ryukyu Group (1.7–1.4 to 0.45 Ma).
terrestrial vertebrate fauna of the islands. Southern OkiNote that reef formation started significantly later on thenawa Jima was uplifted and emerged after ca. 2 Ma andMiyako Islands (1.25 Ma on Irabu Jima and 0.96 Ma on
was temporarily connected to the OMSP, which is likely to
Miyako Jima) than on Okinawa Jima (1.7–1.4 Ma). c Period
have emerged earlier than southern Okinawa Jima, to form
immediately after deposition of the main body of the Ryukyu
a large island extending from Okinawa Jima to the Miyako
Group (ca. 0.4 Ma). d Period after deposition of the main
Islands with a NE–SW direction of ~ 400 km. Subsequently,
body of the Ryukyu Group (ca. 0.4–0.27 Ma). The OMSPOkinawa Jima became separated from the OMSP when thewas almost completely submerged after 0.27 Ma. e Present.
Ryukyu Group—which is composed of Quaternary reef andassociated fore-reef and shelf deposits—began to accumulate around the island at 1.7–1.4 Ma. During the intervalfrom 2.0 to 1.7–1.4 Ma, numerous terrestrial animals, including flightless vertebrates, extended their distribution to
the OMSP. Although the Miyako Islands repeatedly underwent complete submergence during deposition of the mainpart of the Ryukyu Group (1.25–0.4 Ma), they were uplifted and emerged to become a land area after ca. 0.4 Ma.
In contrast, the OMSP subsided after ca. 0.4 Ma and was almost completely submerged after 0.27 Ma. During ca.
0.4–0.27 Ma, terrestrial animals migrated from the OMSP to the Miyako Islands.

Published: 2023/7/20
https://doi.org/10.1186/s40645-023-00567-x― 57 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Biogeosciences

Accessing the energy-limited and sparsely populated deep biosphere: achievements and ongoingchallenges of available technologies
Yuki Morono[Keywords] Subseafloor biosphere, Low energy habitat, Technical developments, Limits of life

Microbes in marine sediments detected and counted bydirect observation of membrane-filtered sediment samples
stained with acridine orange. This technique can still beapplied to high-biomass (>105 cells/cm3) sedimentary habitats, such as organic-rich sediments collected in shallow areas
near the seafloor. However, to further explore the nutrientsand energy turnover under extremely low energy flux conditions, or in habitats that are close to the lower limit of thebiosphere, technological breakthroughs have been required toincrease the detection sensitivity for microbial life at densities
of a few cells/cm3 of sediment. These technological developments contributed to increasing fundamental information on
microbial life at the fringes of the subseafloor biosphere andled to the discovery of revivable microbes in sediments aged
up to 101.5 million years old. More recently, chemical detection
methods have revealed the existence of spores in the deep
biosphere that are impermeable to conventional DNA stains.
Previous applications of molecular biology-based approaches
have been limited to relatively higher biomass samples, potentially because the cells surviving in these very low energy flux
environments have less integrated genomes. Here, I review

Cartoon diagram of the subseafloor biosphere. The

the contribution and importance of the technological develop-

increasing challenges for the survival of microbes arements that have been made in the study of microbes fromillustrated toward the depth of subseafloor.

the subseafloor biosphere, recent developments of alternative
methods to microscopically detect microbial spores and their application to deep subseafloor sediments, and the challenges associated with applying molecular biological approaches to study low-biomass samples.

Published: 2023/4/10
https://doi.org/10.1186/s40645-023-00551-5― 58 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Biogeosciences

Liquid and supercritical CO2 as an organic solvent in Hadean seafloor hydrothermal systems:
implications for prebiotic chemical evolution
Takazo Shibuya, Ken Takai[Keywords] Origin of life, Liquid and supercritical CO2, CO2 hydrate, Seafloor hydrothermal vent, Prebiotic chemical
evolution, Phase separation, Organic solvent, Interface reaction, Metal dissolution

Prebiotic chemical evolution and the emergence oflife in the seafloor hydrothermal systems of Hadean
Earth is among the most plausible and popular hypotheses for the origin of earthly life. In contrast, manystudies pointed out that this hypothesis intrinsicallyharbors a critical unsolved problem called the “waterparadox”: Abundant water limits dehydration synthesis and instead facilitates hydrolysis of organic molecules during the early stage of chemical evolution.
However, many of these criticisms have not referred tothe abundant liquid/supercritical CO2 (L/SC-CO2) fluids and pools in modern hydrothermal systems, which
not only create dry environments but also behave ashydrophobic solvents at and beneath the seafloor. In
this paper, we theorize the generation and preservationof a L/SC-CO2 pool in modern seafloor hydrothermal
systems and reinterpret the fossil hydrothermal systems preserved in early Archean seafloor basalts. The
theoretical estimation of subseafloor phase separationand phase segregation of CO2-rich hydrothermal fluids
suggests the presence of L/SC-CO2 fluids and pools in
Hadean seafloor hydrothermal systems. Because they
behave as hydrophobic organic solvents, L/SC-CO2 canpotentially initiate the dehydration synthesis of organic
molecules in seafloor hydrothermal systems. Moreover,at the interface between L/SC-CO2 and H2O-rich fluid(seawater or hydrothermal fluid), amphiphilic molecules
might be generated and triggered into self-assembled
growth. Based on the abundant occurrence and physicochemical properties of L/SC-CO2 fluids, we propose
a new stepwise concept for the origin of life, whereby
prebiotic chemical evolution was co-hosted and facilitated by L/SC-CO2 in Hadean water-rich seafloorhydrothermal systems. This “liquid/supercritical CO2
hypothesis” potentially overcomes the water paradox
and strengthens the idea that earthly life was hatchedin deep-sea hydrothermal systems.

Schematic of Hadean seafloor hydrothermal systems bearing aliquid/supercritical CO2 (L/SC-CO2) pool. The CO2-rich seawater
infiltrates the subseafloor volcanic rocks and reacts with basalts
or komatiites, causing carbonation and alteration of basalts or serpentinization of komatiites in the seawater recharge zones. Whenhydrothermal fluid reaches the reaction zone, it receives abundantdegassed CO2 from an underlying magmatic heat source. During
fluid upwelling, phase separation of the CO2-rich hydrothermal fluid
progressively occurs through depressurization, which likely condenses the CO2 in the vapor phase. If the CO2-rich vapor phaseis physically segregated from the main flow channel of the upwelling brine phase, it is continuously mixed with recharged seawater
and/or cooler pore fluid, causing further phase separation by thetemperature decrease. CO2 is then purified in vapor phase. Eventually, these condensation and purification processes generate many
SC-CO2 droplets beneath the seafloor. The SC-CO2 is less dense
than seawater and migrates upward. As it cools during the upwardmigration, its phase converts to L-CO2. These processes form alarge L/SC-CO2 pool beneath the seafloor. If the temperature of
the bottom seawater is lower than approximately 10 °C, reactions
between L-CO2 and the ambient seawater/pore fluid requisitely
generate solid CO2 hydrates that cement the pores, voids andcavities of the hydrothermal sediments and permeable volcanics.
This self-sealing effect by CO2 hydrates prevents the leakage of L/
SC-CO2 through the seafloor. In contrast, when CO2 hydrates areabsent in the vicinity of warm/hot hydrothermal vents, L/SC-CO2
leaks from the inner edge of the pool and enters the upwelling hydrothermal fluid just below the seafloor, where it is emitted in the formof bubbles. L-CO2 containing these bubbles transforms to hydratecoated L-CO2 during upward migration through the water column.
The bubbles disappear at depths around 500 m because L-CO2 andCO2 hydrate are unstable at these depths. Eventually, both CO2 gas
and the organic molecules dissolved in L/SC-CO2 are released tothe ambient seawater. If the hydrothermal vents are black-smoker
type, the L-CO2 bubbles will carry heavy metals upward to the shallower part of the water column.

Published: 2022/11/15
https://doi.org/10.1186/s40645-022-00510-6― 59 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Biogeosciences

Perspective on the response of marine calcifiers to global warming and ocean acidification –Behavior of corals and foraminifera in a high CO2 world “hot house”
Kawahata H, Fujita K, Iguchi A, Inoue M, Iwasaki S, Kuroyamagi A, Maeda A, Manaka T, Moriya K, Takagi H,
Toyofuku T, Yoshimura T, Suzuki A[Keywords] Partial pressure of CO2, Global warming, Ocean acidification, Coral, Foraminifera, Bleaching, Calcite,
Aragonite, Saturation state, Organic matter, Alkalinity, Carbon cycle

The CO2 concentration of air has increased over the last two
centuries and recently surpassed 400 ppm. Carbon cycle models project CO2 concentrations of 720 to 1000 ppm for the IPCC
intermediate scenario (RCP 6.0), resulting in an increase in global
mean temperature of ~2.6 °C and a decrease in seawater pH of~0.3. Together, global warming and ocean acidification are often
referred to as the “evil twins” of climate change, potentially inducing severe threats in the near future. In this paper, our discussion
is focused on the response of two major calcifiers, foraminifera
and corals, which contribute much to the global carbonate burial
rate. Photosymbiosis is regarded as an adaptive ecology for living in warm and oligotrophic oceans, especially for reef-building
corals and larger reef-dwelling benthic foraminifera. As a consequence of global warming, bleaching may be a global threat toalgal symbiont-bearing marine calcifying organisms under conditions of high temperature and light intensity. If CO2 is dissolved
in seawater, the partial pressure of CO2 in seawater (pCO2) anddissolved inorganic carbon (DIC) increases while pH and the saturation state of carbonate minerals decreases without any change
Fig. 1. Comparison of an acidification condition experin total alkalinity. Generally, marine calcifying organisms show
iment and the growth weight of foraminifera.
decreases in calcification rates in response to acidified seawaFig. 2. Schematic diagram of ocean acidification andter. However, the response often differs depending on situations,the buffering system in the Earth’s surface system.
species, and life-cycle stage. Some benthic foraminifera showed
a positive response to low pH conditions. The Acropora digitifera
coral calcification of adult branches was not reduced markedly at higher pCO2 conditions, although calcification tended
to decrease versus pCO2 in both aposymbiotic and symbiotic polyps. New analytical technologies help identify important constraints on calcification processes. Based upon Ca isotopes, the transport path of Ca2+ and the degree of its
activity would predominantly control the carbonate precipitation rate. Visualization of the extracellular pH distribution
shows that proton pumping produces the high internal pH and large internal–external pH gap in association with foraminiferal calcification. From the perspective of a long-term change in the Earth’s surface environment, foraminifera
seem to be more adaptive and robust than corals in coping with ocean warming and acidification but it is necessary
to further understand the mechanisms underlying variations in sensitivity to heat stress and acidified seawater for
future prediction. Since CO2 is more soluble in lower temperature seawater, ocean acidification is more critical in thepolar and high-latitude regions. Additionally, older deep-water has enhanced acidity owing to the addition of CO2 fromthe degradation of organic matter via a synergistic effect with high pressure. With current ocean acidification, pH
and the saturation state of carbonate minerals are decreasing without any change in total alkalinity. However, in the
Earth’s history, it is well known that alkalinity has fluctuated significantly. Therefore, it is necessary to quantitatively
reconstruct alkalinity, which is another key factor determining the saturation state of carbonate minerals. The rapid
release of anthropogenic CO2 (in the present day and at the Paleocene/Eocene boundary) induces severe ocean
acidification, whereas in the Cretaceous, slow environmental change, even at high levels of pCO2, could raisealkalinity, thereby neutralizing ocean acidification.
Published: 2019/1/17
https://doi.org/10.1186/s40645-018-0239-9― 60 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Biogeosciences

Theoretical constraints of physical and chemical properties of hydrothermal fluids on variations
in chemolithotrophic microbial communities in seafloor hydrothermal systems.
Nakamura K, Takai K[Keywords] Deep-sea hydrothermal systems, Chemosynthetic ecosystems, Hydrothermal fluid chemistry, Host rockgeochemistry, Geochemical modeling, Bioavailable energy yieldIn the past few decades, chemosynthetic
ecosystems at deep-sea hydrothermal vents
have received attention as plausible analogues
to the early ecosystems of Earth, as well as toextraterrestrial ecosystems. These ecosystems
are sustained by chemical energy obtained frominorganic redox substances (e.g., H2S, CO2, H2,
CH4, and O2) in hydrothermal fluids and ambient seawater. The chemical and isotope compositions of the hydrothermal fluid are, in turn,controlled by subseafloor physical and chemical processes, including fluid–rock interactions,
phase separation and partitioning of fluids, andMetabolic energies available from each (Left) aerobic and (Right) anaero-precipitation of minerals. We hypothesized thatbic reactions for chemolithoautotrophy considered in this study

specific physicochemical principles describe thelinkages among the living ecosystems, hydrothermal fluids, and geological background in deep-sea hydrothermal
systems. We estimated the metabolic energy potentially available for productivity by chemolithotrophic microorganisms at various hydrothermal vent fields. We used a geochemical model based on hydrothermal fluid chemistry datacompiled from 89 globally distributed hydrothermal vent sites. The model estimates were compared to the observed
variability in extant microbial communities in seafloor hydrothermal environments. Our calculations clearly show that
representative chemolithotrophic metabolisms (e.g., thiotrophic, hydrogenotrophic, and methanotrophic) respond differently to geological and geochemical variations in the hydrothermal systems. Nearly all of the deep-sea hydrothermal
systems provide abundant energy for organisms with aerobic thiotrophic metabolisms; observed variations in the
H2S concentrations among the hydrothermal fluids had little effect on the energetics of thiotrophic metabolism. Thus,
these organisms form the base of the chemosynthetic microbial community in global deep-sea hydrothermal environments. In contrast, variations in H2 concentrations in hydrothermal fluids significantly impact organisms with aerobic
and anaerobic hydrogenotrophic metabolisms. Particularly in H2-rich ultramafic rock-hosted hydrothermal systems,
anaerobic and aerobic hydrogenotrophy is more energetically significant than thiotrophy. The CH4 concentration also
has a considerable impact on organisms with aerobic and anaerobic methanotrophic metabolisms, particularly in sediment-associated hydrothermal systems. Recently clarified patterns and functions of existing microbial communities
and their metabolisms are generally consistent with the results of our thermodynamic modeling of the hydrothermal
mixing zones. These relationships provide important directions for future research addressing the origin and early
evolution of life on Earth as well as for the search for extraterrestrial life.

Published: 2014/4/22
https://doi.org/10.1186/2197-4284-1-5― 61 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Biogeosciences

Biochemical and physiological bases for the use of carbon and nitrogen isotopes in environmental and ecological studies
Ohkouchi N, Ogawa N O, Chikaraishi Y, Tanaka H, Wada E[Keywords] Carbon isotopic composition, Nitrogen isotopic composition, Ecosystem, Food web, Chlorophyll, Trophic
position, Amino acid, Animal organ

We review the biochemical and physiologicalbases of the use of carbon and nitrogen isotopic
compositions as an approach for environmental and ecological studies. Biochemical processes commonly observed in the biosphere,
including the decarboxylation and deaminationof amino acids, are the key factors in this isotopic approach. The principles drawn from theisotopic distributions disentangle the complex
dynamics of the biosphere and allow the interactions between the geosphere and biosphereto be analyzed in detail. We also summarize two
recently examined topics with new datasets: theisotopic compositions of individual biosynthetic
products (chlorophylls and amino acids) andthose of animal organs for further pursuing thebasis of the methodology. As a tool for investigating complex systems, compound-specificisotopic analysis compensates the intrinsic disadvantages of bulk isotopic signatures. Chlorophylls provide information about the particular
processes of various photoautotrophs, whereas
amino acids provide a precise measure of theTrophic positions of organisms from Lake Baikal based on the nitrogen

trophic positions of heterotrophs. The isotopic

isotopic composition of amino acids (glutamic acid and phenylalanine).

distributions of carbon and nitrogen in a single“TP” denotes trophic position.

organism as well as in the whole biosphere arestrongly regulated, so that their major components such as amino acids are coordinated appropriately rather thancontrolled separately.

Published: 2014/2/3
https://doi.org/10.1186/s40645-015-0032-y― 62 ―

Review
Solid earth sciences

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Reconsideration of the energy balance in earthquake faulting
Mitsuhiro Matsu’ura[Keywords] Theoretical seismology, Background stress field, Earthquake faulting, Moment tensor, Inelastic strain,
Elastic potential energy, Radiated seismic energy, Work done for shear faulting, Fault constitutive law, Rupture growthrate

The occurrence of earthquakes is now understoodas brittle shear fracture releasing the elastic potential
energy stored in the earth. Since the 1950s, manystudies on the energy balance in earthquake faulting have been done, but there seems to be someincoherence among them. The essential reason is
because various changes in conceptual framework
happened during the last six decades, specifically the
introduction of the new paradigm of plate tectonics inthe 1960s, the concept of moment tensor as source
representation in the 1970s, and the fault constitutive
law governing rupture growth in the 1990s. Therefore,
it will be worthwhile to reconsider the energetics ofearthquake faulting from a current perspective. For
this purpose, first of all, we summarize the basic con-

A schematic diagram showing the difference in rupture growth
path between the dynamic and quasi-static cases. The thick graycurve τ = τdy (D) and white curve τ = τqs (D) represent the dynamicand quasi-static rupture growth paths, respectively. For reference,the slip-weakening curve τ = τfr (D) is also plotted in black. The

cepts of elastic potential energy and moment tensor

symbols τi, τp, τr, and τf indicate the initial, peak, residual, and final

and review the general representation of earthquake

values of the shear stress τ, respectively. The dynamic rupturesources and the origin of background crustal stressgrowth path is characterized by the initial slip-weakening phase,to confirm that the effect of earth’s self-gravitation is

the intermediate high-speed rupture propagation phase, and thenegligible in the energetics of shear faulting. Next,

final slip deceleration and transient adjustment phase. The area

as a starting point for discussion, we directly derive∫ [Τ (D) -Τ (D)] dD,
gives the total seismic energy escaping from the mechanical systema basic equation of mechanical energy balance inconcerned.

enclosed by the thick gray and white curves,

Dfinaldy

qs

0

dynamic shear faulting from the equation of motion
for an elastic body subjected to tectonic-origin deviatoric stress. Then, we review the widely accepted formula forindirectly evaluating radiated seismic energy from a simplified energy balance equation and compare with the direct
evaluation based on the analytical solution of displacement fields for a point dislocation source in order to call attention
to inconsistency between them. The inconsistency comes from the omission of the effects of rupture growth rate in
the simplified energy balance equation. So, finally, we review the energy balance at the tips of a propagating shear
crack, which naturally leads to the introduction of the slip-weakening fault constitutive law as a fundamental equation
governing earthquake rupture. Then, we discuss the whole process of earthquake rupture, consisting of initiation,
acceleration, steady propagation, deceleration, and termination from the viewpoint of energy balance.

Published: 2024/1/9
https://doi.org/10.1186/s40645-023-00602-x― 64 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

An introductory review of the thermal structure of subduction zones: II—numerical approach andvalidation
Cian R. Wilson, Peter E. van Keken[Keywords] Geodynamics, Plate tectonics, Finite element methods, Subduction zone metamorphism, Arc volcanism

The thermal structure of subduction zones is fundamental to our understanding of the physical and chemical processes that occur at active convergent plate margins. These
include magma generation and related arc volcanism, shallow and deep seismicity, and metamorphic reactions thatcan release fluids. Computational models can predict thethermal structure to great numerical precision when models
are fully described but this does not guarantee accuracy orapplicability. In a trio of companion papers, the constructionof thermal subduction zone models, their use in subduction

Steady-state thermal structure for the updated subduction

zone studies, and their link to geophysical and geochemicalzone benchmark. a) Temperature predicted by TF

observations are explored. In this part II, the finite element(TerraFERMA) for case 1 (constant viscosity h = 1); b)
temperature difference between TF and Sepran using thetechniques that can be used to predict thermal structure

penalty function (PF) method for case 1 at fm = 1 where fm

are discussed in an introductory fashion along with theirrepresents the smallest element sizes in the finite element

verification and validation.

grids near the coupling point; c) slab top temperature

Steady-state thermal structure for the updated subduc-comparison for case 1; and d)–f) as a)–c) but now for case 2tion zone benchmark. a) Temperature predicted by TF for(temperature and strain rate dependent viscosity). The starcase 1; b) temperature difference between TF and Sepran

indicates the position or temperature conditions at the
coupling point.

using the penalty function (PF) method for case 1 at fm = 1
where fm represents the smallest element sizes in the finite

element grids near the coupling point; c) slab top temperature comparison for case 1; and d)–f) as a)–c) but now forcase 2. The star indicates the position or temperature conditions at the coupling point.

Published: 2023/11/30
https://doi.org/10.1186/s40645-023-00588-6― 65 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Recent progress in research on source processes of great earthquakes using tsunami data
Yuichiro Tanioka, Yusuke Yamanaka[Keywords] Research on source processes, Great earthquakes, Progress in tsunami researchThis paper provides an overview of inverse
studies that estimate earthquake source processes using tsunami-related data. Methods
and techniques developed with those data associated with the 2004 Sumatra and 2011 Tohokuoki earthquakes were reviewed. These events
significantly impacted subsequent studies that
focused on great historical earthquakes. Thus,
recent advancements from studies on great historical earthquakes (M > 8) using old tsunami
data, including documents and non-digital tsunami waveforms, have been reviewed. Anotherkey earthquake was the 1700 Cascadia earth-

Sources of great earthquakes in Sumatra, Indonesia (left) and those inquake, and its source process was revealed

Northern Japan, off Hokkaido and Tohoku, (right) discussed in this paper.

using geological tsunami deposit data, whichhave led to a recent surge in prehistorical earthquake studies using tsunami deposit data. Considering this, theadvancements in prehistorical earthquake studies have been reviewed. Finally, expected advancements in earthquake
source process studies using tsunami-related data in the near future have been discussed.

Published: 2023/10/8
https://doi.org/10.1186/s40645-023-00593-9― 66 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

An introductory review of the thermal structure of subduction zones: III—Comparison between
models and observationsPeter E. van Keken, Cian R. Wilson[Keywords] Geodynamics, Plate tectonics, Finite element methods, Subduction zone metamorphism, Arc volcanism

The thermal structure of subduction zones is fundamental to our understanding of the physical and chemical processes that occur at active convergent plate margins. These
include magma generation and related arc volcanism, shallow and deep seismicity, and metamorphic reactions thatcan release fluids. Computational models can predict thethermal structure to great numerical precision when models
are fully described but this does not guarantee accuracy orapplicability. In a trio of companion papers, the constructionof thermal subduction zone models, their use in subduction
zone studies, and their link to geophysical and geochemical
Comparison between TerraFERMA and Sepran predictions forobservations are explored. In this last part, we discuss how

the thermal structure of the models for Cascadia (row a),

independent finite element approaches predict the thermal

Alaska Peninsula (row b), and Central Honshu (row c).

structure of the global subduction system and investigate

Column 1: Temperature as predicted by TerraFERMA. Slabhow well these predictions correspond to geophysical, geo-

top is indicated by the solid line and the slab Moho by thechemical, and petrological observations.

dashed line. Column 2: Temperature difference between
predictions from TerraFERMA and Sepran. Slab top andMoho indicated as in column 1. Column 3: Comparison of thetemperature at the slab top and slab Moho. Lines are from
TerraFERMA (slab top solid lines, slab Moho dashed lines),
open circles are from Sepran

Published: 2023/9/18
https://doi.org/10.1186/s40645-023-00589-5― 67 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Seismic noise between 0.003 Hz and 1.0 Hz and its classification
Toshiro Tanimoto, Aaron Anderson[Keywords] Low-frequency seismic noise, Ocean–solid earth interaction, Wave–wave interaction, Quasi-static
deformation

It is now established that the primary microseism, thesecondary microseisms, and the hum are the three main
components of seismic noise in the frequency band fromabout 0.003 Hz to 1.0 Hz. Monthly averages of seismic
noise are dominated by these signals in seismic noise.
There are, however, some temporary additional signals
in the same frequency band, such as signals from tropical cyclones (hurricanes and typhoons) in the ocean andon land, stormquakes, weather bombs, tornadoes, andwind-related atmospheric pressure loading. We review
these effects, lasting only from a few hours to a week
but are significant signals. We also attempt to classify
all seismic noise. We point out that there are two broadtypes of seismic noise, the propagating seismic waves
and the quasi-static deformations. The latter type isobserved only for surface pressure changes at close distances. It has been known since about 1970 but has notbeen emphasized in recent literature. Recent data basedon co-located pressure and seismic instruments clearlyshow its existence. Because the number of phenomenain the first type is large, we propose to classify all seismic
noise into three categories: (1) propagating seismic waves
from ocean sources, (2) propagating seismic waves fromon-land sources, and (3) quasi-static deformation at ocean
bottom and on land. The microseisms and the hum arein the first category although there are differences in thedetailed processes of their excitation mechanisms. We will
also classify temporary signals by these categories.

Figure:(a) Beamforming for P-wave sources by an array analysis of theSouthern California Seismic Network. There was a P-wave sourcenear Hurricane Sandy when it (its center indicated by a whitesquare) moved northward off the East coast of USA. In the sametime interval, a low-pressure system in the northern Pacific Ocean
was also emitting P waves. Body waves are often excited near alow-pressure system through the wave-wave interaction of ocean
waves.
(b) Pressure inside a tornado is much lower than the ambient
atmospheric pressure. When a tornado touches the Earth’s surface, it acts as a single force because of this pressure difference
and excites seismic waves. The excitation source strength, inverted
from seismic data, matches the temporal variation of the Fujita
scale determined for a tornado.
(c) In the frequency band 0.3-1.0 Hz, a slightly higher frequency
band than the secondary microseism, we can see seismic noisecaused by the wave-wave interaction of local ocean waves that inturn were generated by local winds. High amplitudes in seismic
waves (top) and ocean waves (middle) are indicated by white andshow close agreements in their temporal behavior. Wind speed(bottom) also shows a good correlation with ocean wave data,
especially if we focused on high speed time intervals.
(d) Plot of vertical seismic PSD against pressure PSD allows us
to separate the propagating seismic signals from distance sources
and the loading ground deformation signals from local pressuresources. For pressure less than the one indicated by the verticaldashed line, the signals are propagating seismic waves from distantsources because their amplitudes are not affected by local pressure variations. For pressure higher than the dashed line, verticalseismic amplitudes increase with local pressure, indicating thatthey are generated by local surface pressure loading. Data fromtwo EarthScope Transportable stations (KMSC, U57A) were used.
Each point is from an analysis of 1-hour-long time series and thedata were from the year 2014.

Published: 2023/9/11
https://doi.org/10.1186/s40645-023-00587-7― 68 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

The nature of the Pacific plate as subduction inputs to the northeastern Japan arc and its
implication for subduction zone processes
Gou Fujie, Shuichi Kodaira, Koichiro Obana, Yojiro Yamamoto, Takehi Isse, Tomoaki Yamada, Tetsuo No,
Yasuyuki Nakamura, Seiichi Miura[Keywords] Incoming oceanic plate, Oceanic crust, Controlled-source seismic survey, Japan Trench, Outer rise, Tohoku
earthquake

Devastating megathrust earthquakes andslow earthquakes both occur along subducting
plate interfaces. These interplate seismic activities are strongly dependent on the nature of theplate interface, such as the shape of the plateinterface and the materials and physical conditions along the plate interface. The oceanic
plate, which is the input to the subduction zone,
is the first order control on the nature of theplate interface. To reveal the nature of the subduction inputs to the northeastern Japan arc, we(left) Map of the study area. Red lines show multi-channel seismic

have conducted large-scale controlled-source(MCS) reflection survey lines and white circles represent Ocean Bottom

seismic surveys of the northwestern part ofSeismometers (OBSs) deployed along some of survey lines to obtain

the oceanic Pacific plate. The obtained seismic
data have revealed (1) oceanic plate structuralwide-angle seismic reflection and refraction data. (right) Map of the crustal
thickness in two-way time derived from all the MCS lines, showing notableregional variations.

evolution caused by plate bending prior to subduction, suggesting the promotion of the oceanic plate hydration; (2) spatial variation of the oceanic plate structure,such as variations in the thickness of sediment and crust; (3) that the spatial variations are caused by both ancientplate formation processes and more recent volcanic activities; and (4) that spatial variations of the nature of the subduction inputs show good correlation with the along-strike variations in the seismic structure and seismic activities
after subduction, including the coseismic slip distribution of the 2011 Tohoku earthquakes and the structural differences
between the northern and the southern Japan Trench. These observations indicate that the incoming oceanic plate
structure is much more spatially variable than previously thought and also imply that the spatial variation of the subduction inputs is a key controlling factor of the spatial variation of various processes in subduction zones, includinginterplate seismic activities and evolution of the forearc structure.

Published: 2023/8/22
https://doi.org/10.1186/s40645-023-00578-8― 69 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Progress in modeling the Tohoku-oki megathrust earthquake cycle and associated crustal
deformation processes
Bunichiro Shibazaki[Keywords] 2011 Tohoku-oki earthquake, Numerical modeling, Megathrust earthquake cycle, Hierarchical asperity
model, Dynamic weakening, Postseismic deformation, Viscoelastic relaxation, Postseismic slip, Long-term verticaldeformation

This paper summarizes the results of 10 years of
research on models of the megathrust earthquake
cycles and crustal deformation associated with the 2011
Tohoku-oki earthquake. Several earthquake cycle models have been proposed for the northeast Japan subduction zone to elucidate why megathrust earthquakes
occur at intervals of approximately 600 years and whylarge slips occurred in the shallow subduction zone. A
model that considers a strong asperity in the shallow
plate interface, and a hierarchical asperity model thatconsiders the scale dependence of the critical displacement of the rate- and state-dependent friction law havebeen proposed. Modeling with dynamic weakening of

Examples of modeling of megathrust earthquake cycles andfaults has also been proposed. In the model using thepostseismic deformation for the 2011 Tohoku-oki earthquake andshallow friction characteristics obtained by the Japan

long-term vertical crustal deformation prior to the Tohoku-oki

Trench Fast Drilling Project, rupture from depth canearthquake presented in this paper. (Left) Distribution of friction

propagate to the trench, resulting in shallow large slips.
Submarine crustal deformation has been observed forthe first time in addition to dense observations of theparameters used in the earthquake cycle model (Shibazaki et al.
2019), considering shallow fault friction properties obtained fromJFAST. Regions, where a-b is negative, indicate asperities ofvelocity weakening. (Right top) Modeling of postseismic

inland crustal deformation. The observation of the sea-

deformation (Agata et al. 2019). Total displacement of the crust

floor deformation near the trench showed that visco-and mantle and viscosity of the mantle 2.8 years after theelastic relaxation played an important role in short-term

Tohoku-oki earthquake. The Tohoku-oki earthquake caused large

postseismic deformation near the trench. The effects ofstress fluctuations, resulting in a sudden viscosity decrease andthe low-viscosity region at the oceanic lithosphere andrapid flow in the asthenosphere below the oceanic lithosphere.
(Right bottom) Modeling of vertical crustal deformation rates andasthenosphere boundary, and the cold forearc mantle

motions in the island arc crust and mantle prior to the Tohoku-oki

wedge (cold nose) have been discussed. Simulations

earthquake (Sasajima et al. 2019). The model reproduced theusing the nonlinear flow law of rock in the mantle,

subsidence of the Pacific coast of northeast Japan observed forwhere a power–law relationship holds between stressabout 100 years prior to the Tohoku-oki earthquake.

and strain rate, and the fault friction law at the plateboundary, show that the Tohoku-oki earthquake caused large stress fluctuations, resulting in a sudden viscosity
decrease and rapid flow in the asthenosphere below the oceanic lithosphere. The simulations of the crustal deformation associated with the Tohoku-oki earthquake cycle also indicate that in the later stage of the earthquake cycle,
the Pacific coastal region begins to subside due to the increasing slip deficit rate on the deeper parts of the plateinterface. These results explain the subsidence of the Pacific coast of northeast Japan observed for about 100 years
prior to the Tohoku-oki earthquake. In the future, a model that explains the long-term crust and mantle deformation
during the entire Tohoku-oki earthquake cycle must be constructed.
Published: 2023/7/31
https://doi.org/10.1186/s40645-023-00575-x― 70 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

An introductory review of the thermal structure of subduction zones: I—motivation and selected
examplesPeter E. van Keken, Cian R. Wilson[Keywords] Geodynamics, Plate tectonics, Finite element methods, Subduction zone metamorphism, Arc volcanism

The thermal structure of subduction zones is fundamental
to our understanding of physical and chemical processes
that occur at active convergent plate margins. These
include magma generation and related arc volcanism, shallow and deep seismicity, and metamorphic reactions thatcan release fluids. Computational models can predict thethermal structure to great numerical precision when models
are fully described but this does not guarantee accuracy orapplicability. In a trio of companion papers, the constructionof thermal subduction zone models, their use in subduction
zone studies, and their link to geophysical and geochemical observations are explored. In part I, the motivation tounderstand the thermal structure is presented based on
experimental and observational studies. This is followed bya description of a selection of thermal models for the Japanese subduction zones.

Subduction zone processes and example of thermal
structure. a Cartoon of subduction zone processes (modified
from van Keken (2003)). b Thermal structure predicted for
Tohoku subduction (van Keken et al. (2012)). c Temperatureof the top of the oceanic crust (in red) and oceanic Moho (ingreen) as a function of lithostatic pressure P and depth.

Published: 2023/7/28
https://doi.org/10.1186/s40645-023-00573-z― 71 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Si- versus Mg-metasomatism at the crust–mantle interface: Insights from experiments, naturalobservations and geochemical modeling
Atsushi Okamoto, Ryosuke Oyanagi[Keywords] Element mobility, Metasomatism, Crust–mantle interface, Fluid, Chloritization

The slab–mantle interface in subduction
zones is one of the geological boundaries withthe most significant chemical potential gradients, which leads to fluid-mediated metasomatic
reactions and chemical transport. As subducting
sediment and basaltic crust often contain silica in various forms, the Si-metasomatism ofmantle rocks is thought to occur along the subduction zone interface. However, growing evidence from the geochemistry of altered rocks
and thermodynamic modelling has revealed
the presence of multi-component fluids at theslab interface. Here, we review the laboratory
experiments, geochemical models, and naturalobservations that improve our understanding

Results of geochemical modeling showing the relative mobility of Mg andof mass transport and metasomatic reactions

Si along the geotherm of the representative subduction zones (left panel)at the crust–mantle interface, focusing on therelative mobility of Mg and Si. Hydrothermal
experiments using analogues for the boundaryand schematic illustrations of Si- and Mg-metasomatism at the crustmantle interfaces within the warm (right top) and cold subduction zones(right bottom).

between mantle (olivine) and crust (quartz or plagioclase) under vapor-saturated pressures indicate that Si is preferentially transported from crust to mantle, whereas Mg is immobile. This result is consistent with the distribution oftalc rocks in oceanic lithosphere. On the other hand, at the contact between ultramafic (e.g., serpentinite) and crustal(pelitic schist or basaltic rocks) rocks in high-pressure metamorphic terranes, a large volume of chlorite rocks form in
the crustal rocks, and the volume of chlorite often exceeds talc in serpentinites. Geochemical modeling reveals thatin the shallow part of a subduction zone, the dissolved Si content of fluids in equilibrium with pelitic schist (CSi,crust) is
significantly higher than the dissolved Mg content of fluids in equilibrium with mantle peridotite (CMg,mantle); however,CMg,mantle becomes dominant at depth, resulting in the Mg-metasomatism of crustal rocks to form chlorite rocks. This
Mg-metasomatism is more widespread in warmer subduction zones (e.g., the Nankai and Cascadia subduction zones)
than in colder subduction zones (e.g., in Northeast Japan). In addition, the infiltration of CO2-bearing fluid can form
talc (along with carbonates) in ultramafic rocks without Si-metasomatism. Variations in the relative mobility of Si and
Mg at the subduction zone interface produce variations in the overall solid volume change of mantle (expansion orcontraction), the types of sheet silicates (talc versus chlorite), and the fluid budget (dehydration or hydration) duringmetasomatic reactions, which affects the pore fluid pressure, frictional strength of the subduction megathrust, and thelocation of seismicity around the mantle wedge corner.

Published: 2023/7/18
https://doi.org/10.1186/s40645-023-00568-w― 72 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Progress and application of the synthesis of trans-oceanic tsunamis
Shingo Watada[Keywords] Trans-oceanic tsunami, Historical tsunamis recorded in tide gauge, Tsunami in the gravitationally coupled
Earth system, Tsunami phase delay, Tsunami traveltime delay, Tsunami in the eformable Earth, Earthquake fault
parameters studied by tsunami waveforms, Tsunami simulation by the phase correction method, Eulerian and
Lagrangian variables, Free oscillation and forced oscillation of the Earth with an ocean layer, Compressible densitystratifed ocean

Abundant high-quality distant tsunami records from the2010 Maule (Chile) and 2011 Tohoku-Oki earthquakes haverevealed two distinctive features compared to long-wave
tsunami simulations. The records show that the traveltime
delay of the tsunami increases with distance from the earthquakes, and the initial phase reversal of tsunamis appears
and grows systematically. The conventional tsunami theory
cannot explain the observed waveforms and traveltimes of
distant tsunamis, leading to the need for a new theory to
explain and synthesize distant tsunamis. The propagating
elevated sea surface of a tsunami compresses seawater anddeforms the seafloor and the solid Earth. A propagating tsunami changes the mass distribution of the Earth and results

The tsunami generated by the 2011 Tohoku-Oki earthquake

in a spatiotemporal change in gravity, thereby altering the

took almost a day to cross the Pacific Ocean, and its details

propagating tsunami itself. Incorporating these physics, wewere recorded by the tsunami stations (red triangle) installed

developed a new tsunami propagation theory in which a tsu-

on the deep seafloor. The observed tsunami (white line) andnami is naturally treated as a wave in a gravitationally andthe predicted tsunami based on the classic linear long-wave

elastically coupled Earth system composed of solid Earththeory (yellow line) are compared at the two stations circled

layers and an ocean layer. Two distinct tsunami simulationin white.

techniques based on the new tsunami propagation theory
were introduced and confirmed to produce nearly identical tsunami waveforms. One technique treats tsunamis as
free waves within a deformable Earth system, while the other treats tsunamis as external pressure and gravitational
forces acting on the surface of a deformable Earth system. With the new techniques, the waveform and traveltime
differences between the observed and simulated distant tsunamis disappear. Past distant tsunamis recorded bycoastal tide gauges, which were not previously studied due to the traveltime and waveform mismatch problems, havebecome the focus of quantitative tsunami studies analyzing waveforms. New tsunami propagation techniques havebeen applied to the analysis of distant tsunami waveforms from the past 19 events and have helped to unveil the slip
distributions of the past large earthquakes and to determine the earthquake origin time of the trans-Pacific tsunami
events recorded by tide gauges since 1854.

Published: 2023/5/22
https://doi.org/10.1186/s40645-023-00555-1― 73 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Heterogeneous rheology of Japan subduction zone revealed by postseismic deformation of the2011 Tohoku-oki earthquake
Sambuddha Dhar, Jun Muto, Yusaku Ohta, Takeshi Iinuma[Keywords] Postseismic deformation, GNSS observations, viscoelastic relaxation, afterslip, nonlinear rheology,
earthquake deformation cycle, rheological heterogeneity

The 2011 Tohoku-oki earthquake produced
the most well-recorded postseismic deformation of any megathrust earthquake in the world.
Over the last decade, researchers have useda dense and widespread geodetic network ofmore than 1300 Global Navigation Satellite
System (GNSS) stations inland, as well as theabout 50 stations on the seafloor, to investigate
the various deformation sources responsible for

Post-seismic deformation observations for 10 years after the Tohoku
offshore earthquake (left), and the heterogeneous rheological structure
estimated from them (right).

the observed crustal deformation. One of thecontributing mechanisms to this crustal deformation is the stress relaxation of the viscoelastic mantle beneath theJapanese arc. As evident in experimental rock physics and geophysical observations, ambient mantle conditions andrelated rheology are expected to be heterogeneous in space. However, the contribution of such rheological heterogeneities to the postseismic deformation is still poorly understood. Here, we piece together several rheological heterogeneities inferred from the decade-long postseismic deformation of the 2011 Tohoku-oki earthquake. We reviewed
more than twenty postseismic models to understand how viscoelastic earth can influence the postseismic surface
deformation observed after the Tohoku-oki earthquake. Besides, we employed several synthetic models to tease out
the contribution of individual rheological heterogeneities such as depth-dependent rheology of mantle wedge, oceanic asthenosphere, and low-viscosity zone beneath the volcanic front. We demonstrate that the vertical postseismic
observation is the key to unravel rheological complexity beneath northeastern Japan. The broader vertical deformation
pattern reveals the major viscosity contrast between backarc and forearc, and small-scale subsidence detects thepresence of low-viscosity bodies related to arc magmatism. In short, this review paper provides a vista of three-dimensional heterogeneous rheology of viscoelastic earth. These rheological heterogeneities may play a crucial role inbridging the gap between our understanding of different phase of subduction zone earthquake cycle.

Published: 2023/2/28
https://doi.org/10.1186/s40645-023-00539-1― 74 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Significance of the high-pressure properties and structural evolution of gas hydrates for inferring
the interior of icy bodies
Hisako Hirai, Hirokazu Kadobayashi[Keywords] Methane hydrate, Hydrogen hydrate, High-pressure properties, High and low temperatures, Structural
evolution, Transition mechanism, Guest orientational ordering, Molecular dissociation, Icy bodies, Diamond-anvil cell
(DAC)

Hydrogen, methane, and water ice are among
the most abundant materials in the universe.
Based on experimental, theoretical, and spacecraft data, gas hydrates consisting of gas andwater ice have been predicted to exist throughout the universe. This review discusses thehigh-pressure properties of two common gas
hydrates (methane and hydrogen hydrates) at
low and high temperatures based primarily on
experimental results. Gas hydrates consist of awater molecule host and a gaseous guest. They
have a clathrate structure at low pressure anda filled-ice structure at high pressure. The hostencloses the guest, and a specific interaction
occurs between the guest and host, resulting in
unique physical properties. When subjected to

An overview of the structural evolution of (top) MH and (bottom) HH afterpressure, gas hydrates undergo various phasetransition to the filled-ice structure, except for HH-C0. With increasingchanges. Based on pressure and guest size,pressure, the guests undergo stepwise orientational ordering accompanieda general rule for phase changes occurring inby structural changes. Hydrogen-bond symmetrization of the host was

gas hydrates exists. Analysis of the phase-tran-

predicted to occurs at even higher pressures.

sition mechanism shows that some cages aremaintained after the transition to the next clathrate structure, while others are recombined into different cages of thenext structure. This is a novel mechanism that can be called “cage recombination mechanism.” Low-temperature andhigh-pressure experiments have revealed that as the pressure increases, the guest molecules undergo a stepwise
progression of orientational ordering, i.e., restriction of free rotation, which induces structural changes that stabilize thestructure at high pressure. Theoretical studies have predicted that hydrogen-bond symmetrization in the host occurs
at even higher pressures, further stabilizing the structure. Thus, hydrates respond to environmental changes such aspressure to achieve self-organization by the orientational ordering of the guest and hydrogen-bond symmetrization of
the host. Additionally, results of high-temperature and high-pressure experiments conducted at conditions comparable
to those in Neptune’s ice mantle show that methane hydrate decomposes into solid methane and ice VII, both ofwhich melt at further elevated temperatures. Then, the methane molecules undergo further molecular dissociation toform diamonds. These findings are valuable for modeling the interiors of icy planets and understanding how magnetic
fields and heat are generated.

Published: 2023/1/13
https://doi.org/10.1186/s40645-023-00534-6― 75 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

A review on slow earthquakes in the Japan TrenchTomoaki Nishikawa, Satoshi Ide, Takuya Nishimura[Keywords] Japan Trench ,Slow earthquake, Tectonic tremor, Very-low-frequency earthquake, Slow slip event,
Megathrust earthquake, Tohoku-Oki earthquake, Subduction zone, Crustal structure, Geological environment

Slow earthquakes are episodic slow fault
slips. They form a fundamental component ofinterplate deformation processes, along with
fast, regular earthquakes. Recent seismological and geodetic observations have revealed
detailed slow earthquake activity along theJapan Trench—the subduction zone where
the March 11, 2011, moment magnitude (Mw)
9.0 Tohoku-Oki earthquake occurred. In thispaper, we review observational, experimental,
and simulation studies on slow earthquakes
along the Japan Trench and their researchhistory. By compiling the observations of slow
earthquakes (e.g., tectonic tremors, very-lowfrequency earthquakes, and slow slip events)
and related fault slip phenomena (e.g., small
repeating earthquakes, earthquake swarms,
and foreshocks of large interplate earthquakes),
we present an integrated slow earthquake distribution along the Japan Trench. Slow andmegathrust earthquakes are spatially complementary in distribution, and slow earthquakes

Distribution of slow and fast (regular) earthquakes in the Japan Trenchand Nankai Trough. Blue and red symbols indicate areas where slow andfast earthquakes occur, respectively.

sometimes trigger fast earthquakes in theirvicinities. An approximately 200-km-long alongstrike gap of seismic slow earthquakes (i.e., tectonic tremors and very-low-frequency earthquakes) corresponds withthe huge interplate locked zone of the central Japan Trench. The Mw 9.0 Tohoku-Oki earthquake ruptured this locked
zone, but the rupture terminated without propagating deep into the slow-earthquake-genic regions in the northern andsouthern Japan Trench. Slow earthquakes are involved in both the rupture initiation and termination processes ofmegathrust earthquakes in the Japan Trench. We then compared the integrated slow earthquake distribution with thecrustal structure of the Japan Trench (e.g., interplate sedimentary units, subducting seamounts, petit-spot volcanoes,
horst and graben structures, residual gravity, seismic velocity structure, and plate boundary reflection intensity) anddescribed the geological environment of the slow-earthquake-genic regions (e.g., water sources, pressure–temperature conditions, and metamorphism). The integrated slow earthquake distribution enabled us to comprehensively
discuss the role of slow earthquakes in the occurrence process of the Tohoku-Oki earthquake. The correspondencesof the slow earthquake distribution with the crustal structure and geological environment provide insights into theslow-earthquake-genesis in the Japan Trench and imply that highly overpressured fluids are key to understanding thecomplex slow earthquake distribution. Furthermore, we propose that detailed monitoring of slow earthquake activity
can improve the forecasts of interplate seismicity along the Japan Trench.
Published: 2023/1/3
https://doi.org/10.1186/s40645-022-00528-w― 76 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

The role of hydrogen bonds in hydrous minerals stable at lower mantle pressure conditions
Jun Tsuchiya, Elizabeth C. Thompson[Keywords] Hydrous minerals, Ab initio calculation, Hydrogen bond, High pressure, Lower mantle

Over the past few decades, hydrous minerals were
thought to be absent in the lower mantle, due to theirinstability at high-pressure conditions. Recently, however,hydrous phases including phase H (MgSiO4H2), pyrite-type
FeOOH, and δ-AlOOH have been discovered to be thermodynamically stable at lower mantle pressures. Investigations using ab initio calculations methods play a keyrole in identifying these novel phases and determining
their geophysical properties (i.e., compressibility, elasticity,and sound velocities). These calculations suggest that thehydrous minerals which are stable at lower mantle pressure conditions (i.e., phase H, FeOOH, and AlOOH), havesymmetric hydrogen bonds at these pressures. This indicates that hydrogen bond strength is closely connected tothe stability and physical properties of hydrous minerals
at extreme pressures. In this review, we summarize thetheoretical and experimental studies of hydrous minerals
stable at the high-pressure conditions of the Earth’s lower
mantle in light of the role of hydrogen bonding.

The relationship between O...O and O-H distances (upper
panel), and O...O distance and O-H...O angle (lower panel) of
InOOH, AlOOH, FeOOH and DHMSs. It has been shown that
there is a clear difference in compressive behavior betweenhydrous minerals that undergo hydrogen bond symmetrizationand those that do not undergo symmetrization. In minerals
without hydrogen bond symmetrization, the hydrogen bonds
remain asymmetric even under extreme high-pressure
conditions (e.g., 100 GPa).

Published: 2022/11/17
https://doi.org/10.1186/s40645-022-00521-3― 77 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Fluids and physicochemical properties and processes in the Earth
Bjorn Mysen[Keywords] Fluid, Solubility, Thermodynamics, Mass transport, Permeability, Porosity, Wetting angle

The Earth’s fluid budget is dominated by species in the system C–O–H–N–S together withhalogens such as F and Cl. H2O is by far themost abundant. Such fluids are one of the twomain mass transport agents (fluid and magma)
in the Earth. Among those, in particular aqueous fluids are efficient solvents of geochemically important components at high temperatureand pressure. The solution capacity of aqueous
fluids can be enhanced further by dissolved halogens and sulfur. CO2 or nitrogen species has
the opposite effect.
Fluid-mediated transport in the Earth is by fluids passing through cracks at shallow depth andvia percolation channels along grain boundaries
at greater depth. Percolation velocity is linked
to permeability, which, in turn is governed byrock porosity. Porosity is controlled by wetting angles, θ, at the interface between fluid and mineral surfaces. When
θ < 60°, fluid will wet all grain boundaries of an isotropic crystalline material, whereas when greater than 60°, grainboundary wetting does not occur as readily, and fluid-mediated transport efficiency can be greatly reduced. The sizeof the wetting angle is negatively correlated with the solubility of silicate components in the fluids, which means thatfluid composition, temperature, and pressure affect the wetting angles and, therefore, fluid-mediated mass transport
efficiency in the interior of the Earth.
Geophysical and geochemical anomalies in the Earth’s interior have been linked to the presence of fluids. Fluid
infiltration in crustal and mantle rocks will enhance electrical conductivity and seismic wave attenuation. For example,
5–10% H2O-rich fluids in the mantle wedge above subducting plates have been suggested from enhanced electricalconductivity. Similar fluid fractions have been suggested to be consistent with seismic velocities in these regions.
The geochemistry of the crust and the mantle can be affected by fluid-mediated transport of major, minor, and traceelements. When such altered materials serve as source rocks of partial melts, those geochemical alterations also
lead to changes in partial melt compositions. As an example, the presence of such aqueous fluid in the mantle wedge
above subducting and dehydrating subducting slabs is consistent with partial melting of an H2O-bearing mantle wedge
above subducted oceanic crust.

Published: 2022/10/5
https://doi.org/10.1186/s40645-022-00516-0― 78 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

DigitSeis: Software to Extract Time Series from Analogue Seismograms
Miaki Ishii, Hiromi Ishii[Keywords] analogue seismograms, digitization, DigitSeis software

A vast amount of analogue seismograms recorded
between the end of the nineteenth century and late twentiethcentury are often inaccessible for seismological research
since they are not available as digital time series. This manuscript describes freely available software, DigitSeis, thattakes a digital image of an analogue seismic record andreturns waveforms either as a function of their x-y positionon the image or as time–amplitude information. The overall
structure and approach of the software are provided alongwith how they have evolved over different versions. The

Fig.1 Screenshot of DigitSeis version 1.6β (with display ineffectiveness of the software is demonstrated with three

Japanese) showing the short-period vertical recording fromexamples. The first example is a long-period east–west

Tuczon, Arizona between July 15 and 16, 1945. Digitized

seismogram recorded at the Harvard Seismographic Obser-

traces in colour have been overlain on top of the scannedvatory on photographic paper in May of 1938, which con-seismogram image with yellow vertical bars indicating eachtains signals associated with a magnitude 7.7 earthquake

minute (each hour is also labelled in yellow). The largethat occurred off the coast of Northern Ibaraki, Japan. The

arrivals in white are those associated with the Trinity nuclear
test.

second example is an analysis of a 35-mm microfilm copyof the short-period vertical seismogram recorded at Tucson,
Arizona, on July 16, 1945, that shows blast signals fromthe first nuclear bomb detonation. The final example uses
a 70 mm microfiche image of a long-period north–south
seismogram recorded at College, Alaska in December of
1966, which shows a pair of earthquakes with nearly iden-

Fig.2 Part of long-period north-south motion recorded at COL

tical waveforms. The software is, by no means, perfect,

station (College, Alaska) on December 19, 1966.

and discussion of its limitations such as the compatibility(Left) The section of the scanned microfiche image.
(Right) Same image with digitized traces for two of the lines

with pen- and Develocorder-type seismograms is included,

shown in cyan and magenta.

as well as comments about challenges of incorporatingmachine learning into the digitization process.

Published: 2022/10/1
https://doi.org/10.1186/s40645-022-00508-0― 79 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Review of the Early–Middle Pleistocene boundary and Marine Isotope Stage 19
Martin J. Head
[Keywords] Early–Middle Pleistocene, Quaternary, GSSP, MIS 19, Chiba

The Global Boundary Stratotype Section and Point(GSSP) defining the base of the Chibanian Stage andMiddle Pleistocene Subseries at the Chiba section,
Japan, was ratified on January 17, 2020. Although thiscompleted a process initiated by the International Union
for Quaternary Research in 1973, the term Middle Pleistocene had been in use since the 1860s. The Chiba
GSSP occurs immediately below the top of Marine
Isotope Substage (MIS) 19c and has an astronomical
age of 774.1 ka. The Matuyama-Brunhes paleomagnetic reversal has a directional midpoint just 1.1 m
above the GSSP and serves as the primary guide to
the boundary. This reversal lies within the Early-Middle
Pleistocene transition and has long been favoured tomark the base of the Middle Pleistocene. MIS 19 occurs
within an interval of low-amplitude orbital eccentricity
and was triggered by an obliquity cycle. It spans two
insolation peaks resulting from precession minima andhas a duration of ～ 28 to 33 kyr. MIS 19c begins ～791-787.5 ka, includes full interglacial conditions whichlasted for ～ 8-12.5 kyr, and ends with glacial inception
at ～ 774-777 ka. This inception has left an array of

The Quaternary System/Period and its official subdivision as
currently approved by the ICS and ratified by the IUGS EC. The
Upper Pleistocene Subseries has yet to be officially defined.
GSSP = Global Boundary Stratotype Section and Point.

climatostratigraphic signals close to the Early-Middle
Pleistocene boundary. MIS 19b-a contains a series of three or four interstadials often with rectangular-shaped waveforms and marked by abrupt (< 200 year) transitions. Intervening stadials including the inception of glaciation arelinked to the calving of ice sheets into the northern North Atlantic and consequent disruption of the Atlantic meridional
overturning circulation (AMOC), which by means of the thermal bipolar seesaw caused phase-lagged warming eventsin the Antarctic. The coherence of stadial-interstadial oscillations during MIS 19b-a across the Asian-Pacific and North
Atlantic-Mediterranean realms suggests AMOC-originated shifts in the Intertropical Convergence Zone and pacing by
equatorial insolation forcing. Low-latitude monsoon dynamics appear to have amplified responses regionally although
high-latitude teleconnections may also have played a role.

Published: 2021/9/3
https://doi.org/10.1186/s40645-021-00439-2― 80 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Visualizing heterogeneities of earthquake hypocenter catalogs: modeling, analysis, and compensation
Ogata Y
[Keywords] ABIC, Bias compensation, Detection rate function, Empirical Bayesian method, Data heterogeneity,
Hypocenter catalogs, Location corrections, MAP solutions, Magnitude-shift, Smoothness constraints

As basic data for seismic activity analysis,
hypocenter catalogs need to be accurate, complete, homogeneous, and consistent. Therefore, clarifying systematic errors in catalogs is
an important discipline of seismicity research.
This review presents a systematic model-based
methodology to reveal various biases and theresults of the following analyses. (1) It is criticalto examine whether there is a non-stationary
systematic estimation bias in earthquake magnitudes in a hypocenter catalog. (2) Most earthquake catalogs covering long periods are nothomogeneous in space, time, and magnitude
ranges. Earthquake network structures andseismometers change over time, and therefore, earthquake detection rates change overtime and space. Even in the short term, many
aftershocks immediately following large earthquakes are often undetected, and the detection rate varies, dependingon the elapsed time and location. By establishing a detection rate function, the actual seismic activity and the spatiotemporal heterogeneity of catalogs can be discriminated. (3) Near real-time correction of source locations, far from theseismic observation network, can be implemented based on better determined source location comparisons of othercatalogs using the same identified earthquakes. The bias functions were estimated using an empirical Bayes method.
I provide examples showing different conclusions about the changes in seismicity from different earthquake catalogs.
Through these analyses, I also present actual examples of successful modifications as well as various misleading
conclusions about changes in seismic activity. In particular, there is a human made magnitude shift problem includedin the global catalog of large earthquakes in the late nineteenth and early twentieth centuries.

Published: 2021/1/21
https://doi.org/10.1186/s40645-020-00401-8― 81 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Strength models of the terrestrial planets and implications for their lithospheric structure andevolution
Ikuo Katayama[Keywords] Rheological structure, Lithosphere, Elastic thickness, Terrestrial planets

Knowledge of lithospheric strength can help
to understand the internal structure and evolution of the terrestrial planets, as surface topography and gravity fields are controlled mainly
by deformational features within the lithosphere.
Here, strength profiles of lithosphere were calculated for each planet using a recently updated
flow law and taking into account the effect ofwater on lithospheric deformation. Strength isStrength models of terrestrial planets calculated under dry (red lines) andcontrolled predominantly by brittle deformation

wet (blue lines) conditions.

at shallow depths, whereas plastic deformation
becomes dominant at greater depths through its sensitivity to temperature. Incorporation of Peierls creep, in which
strain rate is exponentially dependent on stress, results in the weakening of plastic strength at higher stress levels,and the transition from brittle to ductile deformation shifts to shallower depths than those calculated using conventional
power-law creep. Strength in both the brittle and ductile regimes is highly sensitive to the presence of water, with theoverall strength of the lithosphere decreasing markedly under wet conditions. The markedly low frictional coefficientof clay minerals results in a further decrease in brittle strength and is attributed to expansion of the brittle field. As
plastic strength is influenced by lithology, a large strength contrast can occur across the crust–mantle boundary if
deformation is controlled by ductile deformation. Effective elastic thickness for the terrestrial planets calculated fromthe rheological models indicates its close dependence on spatiotemporal variations in temperature and the presence ofwater. Although application of the strength models to observed large-scale surface deformational features is subject tolarge extrapolation and uncertainties, I emphasize the different sensitivity of these features to temperature and water,
meaning that quantifying these features (e.g., by data from orbiting satellites or rovers) should help to constrain theinternal structure and evolution of the terrestrial planets.

Published: 2021/1/4
https://doi.org/10.1186/s40645-020-00388-2― 82 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Deep mantle melting, global water circulation and its implications for the stability of the ocean
mass
Shun-ichiro Karato, Bijaya Karki, Jeffrey Park
[Keywords] habitability, ocean mass, sea-level variations, mantle transition zone, water in the mantle, deep mantle
melting, water valve

Oceans on Earth are present as a result ofdynamic equilibrium between degassing and regassing through the interaction with Earth’s interior. We
review mineral physics, geophysical, and geochemical studies related to the global water circulation andconclude that the water content has a peak in the
mantle transition zone (MTZ) with a value of 0.1–1
wt% (with large regional variations). When water-rich
MTZ materials are transported out of the MTZ, partial melting occurs. Vertical direction of melt migration is determined by the density contrast between

Processes of water transport across the 410-km with heterogeneous

the melts and coexisting minerals. Because a den-temperaturesity change associated with a phase transformation
occurs sharply for a solid but more gradually for amelt, melts formed above the phase transformation
depth are generally heavier than solids, whereas
melts formed below the transformation depth arelighter than solids. Consequently, hydrous melts
formed either above or below the MTZ return to the
MTZ, maintaining its high water content. However,the MTZ water content cannot increase without
limit. The melt-solid density contrast above the 410
km depends on the temperature. In cooler regions,
melting will occur only in the presence of very waterrich materials. Melts produced in these regions havehigh water content and hence can be buoyant above
the 410 km, removing water from the MTZ. Consequently, cooler regions of melting act as a water
valve to maintain the water content of the MTZ nearits threshold level (~0.1–1.0 wt%). Mass-balance
considerations explain the observed near-constant

Results of model calculations on ocean mass history

sea-level despite large fluctuations over Earth history. Observations suggesting deep-mantle melting are reviewed
including the presence of low-velocity anomalies just above and below the MTZ and geochemical evidence for hydrous
melts formed in the MTZ. However, the interpretation of long-term sea-level change and the role of deep mantle melting in the global water circulation are non-unique and alternative models are reviewed. Possible future directions ofstudies on the global water circulation are proposed including geodynamic modeling, mineral physics and observational
studies, and studies integrating results from different disciplines.
Published: 2020/12/10
https://doi.org/10.1186/s40645-020-00379-3― 83 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

A coupled core-mantle evolution: Review and future prospects
Takashi Nakagawa[Keywords] Geomagnetic field, Earth’s core, Deep mantle, Long-term evolution

In this review, I provide the current status andfuture prospects for the coupled core-mantle
evolution and specifically summarize the constraints arising from geomagnetism and paleomagnetism on the long-term secular variationsof the geomagnetic field. The heat flow acrossthe core-mantle boundary (CMB) is essential for
determining the best-fit scenario that explains
the observational data of geomagnetic secularvariations (e.g., onset timing of the inner core
growth, geomagnetic polarity reversals, andwestward drift) and should include the various
origins of the heterogeneous structures in the
deep mantle that have affected the heat transfer across the core-mantle boundary for billionsof years. The coupled core-mantle evolution
model can potentially explain the onset timingof the inner core and its influence on the longterm geomagnetic secular variations, but it isstill controversial among modeling approaches
on the core energetics because the paleomagnetic data contains various uncertainties. Additionally, with the coupled core-mantle evolution
model in geodynamo simulations, the frequencyof the geomagnetic polarity reversals can be(a) Schematic illustration of the coupled core-mantle evolution system;

explained with the time variations of the heat(b) Zoom-up of the thermal structure across the core-mantle boundary;flow across the CMB. Additionally, the effects(c) Schematic illustration of the feedback mechanism between core andof the stable region in the outermost outer coreto the magnetic evolution are also crucial but

mantle evolution; (d) An example result on the coupled core-mantle evolution model in parameterized mantle convection computation (Upper left:
Thermal structure of the mantle; Upper right; Heat budget in the man-

there would be still uncertain for their feasibility.

tle; Lower left: Size of the inner core as a function of time; Lower right:

However, despite this progress in under-

Magnetic moment). On the magnetic moment, two values of the thermal

standing the observational data for geomag-

conductivity of the Earth’s core are assumed (163 W/m/K and 125 W/m/K).

netic secular variations, there are several unresolved issues that should be addressed in future investigations: (1) initial conditions—starting with the solidification of
the global magma ocean with the onset timing of plate tectonics and geodynamo actions and (2) planetary habitability—how the dynamics of the Earth’s deep interior affects the long-term surface environment change that has been
maintained in the Earth’s multisphere coupled system.

Published: 2020/10/6
https://doi.org/10.1186/s40645-020-00374-8― 84 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Some remarks on hydrogen-assisted electrical conductivity in olivine and other minerals
Shun-ichiro Karato[Keywords] Electrical conductivity, Hydrogen, Water in the mantle, Point defects

Electrical conductivity in minerals is sensitive tohydrogen content, and therefore, it is a potentially
important property from which one can infer hydrogen (water) distribution in the mantle. However,there has been much confusion in the reported
results on hydrogen-assisted conductivity. In thispaper, I review the existing experimental observations on hydrogen-enhanced electrical conductivity in olivine and other minerals to identify thecauses of confusion. Hydrogen loss as well ashydrogen gain could occur during a conductivity
measurement at high pressures and temperatures. Particularly important is the unrecognizedhydrogen gain during an experiment that could
lead to a large degree of error. Many experiments

Electrical conductivity of hydrogen-bearing olivine. There is a system-

were conducted under the conditions where speci-

atic difference between low temperature and high temperature data.

mens were super-saturated with hydrogen making

High temperature data are consistent with geophysically inferred elec-

the validity of those results unclear. A model fortrical conductivity in the asthenosphere.

hydrogen loss is developed showing a strategy bywhich hydrogen loss can be minimized.
When one selects the experimental results in which the influence of hydrogen loss/gain are carefully examined,
there is no major discrepancy among the results from different laboratories except differences between the resultsfrom low and high temperatures. Differences between low-temperature and high-temperature results are caused by thechange in conduction mechanism. At low temperatures, conduction is due to the migration of interstitial (“free”) proton
and is nearly isotropic, whereas conduction at high temperatures is due to the migration of two protons at M-site thatis highly anisotropic. There is no evidence for substantial concentration dependence of activation enthalpy. Observed
exceptionally large concentration dependence reported by Poe et al. (Phys Earth Planet Inter 181:103-111, 2010) is
inconsistent with all other reports and is likely caused by some experimental artifact.
Experimental results in the high-temperature regime explain a majority of geophysical observations on the conductivity of the oceanic asthenosphere: partial melting is not needed in most regions and is rather inconsistent with theobservations on the matured oceanic mantle. Exception is the asthenosphere near the ridge and/or near the trench
where very high conductivity (~0.1 S/m) is reported at the top of the asthenosphere. Partial melting might play somerole in these regions.
Electrical conductivity in the continental lithosphere cannot be attributed entirely to olivine. An important role oforthopyroxene and/or other minor materials (graphite, sulfide) is needed to explain high conductivity reported in someregions such as Bushveld in South Africa.
The largest remaining uncertainty is the degree to which hydrogen affects electrical conductivity in the lower mantle
minerals. Determining the influence of hydrogen on electrical conductivity in lower mantle minerals is critical to makeprogress in understanding the global water circulation.
Published: 2019/8/12
https://doi.org/10.1186/s40645-019-0301-2― 85 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Detection of repeating earthquakes and their application in characterizing slow fault slip
Naoki Uchida[Keywords] Repeating earthquake, Interplate slip, Fault creep, Aseismic slip

Repeating earthquakes (repeaters) that
rupture the same fault area (patch) are interpreted to be caused by repeated accumulation
and release of stress on the seismic patch ina creeping area. This relationship between
repeaters with fault creep can be exploited for
tracking the fault creep (slow slip) based on therepeaters’ activity. In other words, the repeaters
can be used as creepmeters embedded on a
fault. To do this, it is fundamentally important toselect earthquakes that definitely re-rupture in
the same area. The selections are usually done
based on waveform similarity or hypocenter
location. In hypocenter-location based detec-

Estimation of interplate coupling based on repeating earthquake data (b)tion, the precision of the relative location com-and GPS data (a) (after Nomura et al., 2017).

pared with the dimension of earthquake sources
is critical for confirming the co-location of the source area. On the other hand, waveform-similarity-based detectionneeds to use appropriate parameters including high enough frequency components to distinguish neighboring sources.
Inter-event timing (recurrence interval) and/or the duration of a sequence’s activity are good diagnostic features forfinding appropriate detection parameters and eliminating non-repeating events, which are important because an inappropriate selection leads to including triggered sequences that do not re-rupture the same area. Repeaters provide an
independent estimation of creep from geodetic data and such estimations are mostly in good agreement when bothkinds of data are available. Repeater data are especially useful in the deeper part of strike-slip faults and in near-trench
areas of subduction zones where geodetic data’s resolution is usually limited. The repeaters also have an advantage
with geodetic data analysis because they are not contaminated by viscoelastic deformation or poroelastic reboundwhich are prominent postseismic process for large earthquakes and occur outside of faults. On the other hand, thedisadvantages of repeater analysis include their uneven spatial distribution and the uncertainty of the estimates of slip
amount requiring a scaling relationship between earthquake size and slip. There are considerable variations in theinferred slip amounts from different relationships. Applications of repeater analysis illuminate the spatial distribution ofinterplate stable slip, after slip, and spontaneous and cyclic slow slip events that represent important components ofinterplate slip processes in addition to major earthquakes.

Published: 2019/5/29
https://doi.org/10.1186/s40645-019-0284-z― 86 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Nitrogen in the Earth: abundance and transport
Bjorn Mysen[Keywords] Nitrogen, Recycling, Redox, Speciation, Solubility

The terrestrial nitrogen budget, distribution,and evolution are governed by biological andgeological recycling. The biological cycle provides the nitrogen input for the geological cycle,
which, in turn, feeds some of the nitrogen into
the Earth’s interior. A portion of the nitrogenalso is released back to the oceans and theatmosphere via N2 degassing. Nitrogen in silicate minerals (clay minerals, mica, feldspar,
garnet, wadsleyite, and bridgmanite) exists
predominantly as NH4+. Nitrogen also is foundin graphite and diamond where it occurs in elemental form. Nitrides are stable under extremely reducing conditions
such as those that existed during early planetary formation processes and may still persist in the lower mantle. Fromexperimentally determined nitrogen solubility in such materials, the silicate Earth is nitrogen undersaturated. The situation for the core is more uncertain, but reasonable Fe metal/silicate nitrogen partition coefficients (>10) would yield
nitrogen contents sufficient to account for the apparent nitrogen deficiency in the silicate Earth compared with othervolatiles. Transport of nitrogen takes place in silicate melt (magma), water-rich fluids, and as a minor component insilicate minerals. In melts, the N solubility is greater for reduced nitrogen, whereas the opposite appears to be thecase for N solubility in fluids. Reduced nitrogen species (NH3, NH2−, and NH2+) dominate in most environments of themodern Earth’s interior except the upper ~100 km of subduction zones where N2 is the most important species. Nitrogen in magmatic liquids in the early Earth probably was dominated by NH3 and NH2−, whereas in the modern Earth,
the less reduced, NH2+ functional group is more common. N2 is common in magmatic liquids in subduction zones.
Given the much lower solubility of N2 in magmatic liquids compared with other nitrogen species, nitrogen dissolved as
N2 in subduction zone magmas is expected to be recycled and returned to the oceans and the atmosphere, whereas
nitrogen in reduced form(s) likely would be transported to greater depths. This solubility difference, controlled primarily
by variations in redox conditions, may be a factor resulting in increased nitrogen in the Earth’s mantle and decreasing
abundance in its oceans and atmosphere during the Earth’s evolution. Such an abundance evolution has resulted in
the decoupling of nitrogen distribution in the solid Earth and the hydrosphere and atmosphere.

Published: 2019/5/20
https://doi.org/10.1186/s40645-019-0286-x― 87 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Earthquake Early Warning: what does “seconds before a strong hit” mean?
Tajima F, Hayashida T.
[Keywords] Earthquake early warning, effective preparation for seismic safety at recipients’ sites, short-wavelength
ground motion variation

An earthquake early warning (EEW) system is designed
to detect an event, determine its parameters (hypocenter,magnitude, and origin time), and issue an alert to sites/areas
where necessary actions should be taken before destructive
seismic energy arrivals. At present, large-scale EEW systems
are operational in several countries around the world. The
most extensive nationwide EEW system has been operatingin Japan since 2007, and was able to issue alerts broadly
when the moment magnitude (Mw) 9 Tohoku-Oki earthquake
hit in 2011. The casualties caused by this event were far lessthan those caused by other deadly earthquakes (Mw ≥ 6.6)in this century. Many other countries attributed the fewer
death victims to the advanced large-scale EEW system,and plan to install systems similar to Japan’s model. However, the historical and environmental background in Japan,
both in terms of earthquake hazards and safety preparation, differs considerably from other countries. In addition,
EEW systems that use data from a large-scale network (i.e.,“a big-net” hereafter) still have limitations. There are thus
numerous factors that other countries should consider tobenefit from installing a Japan-styled EEW. In this article,(top)

we review how research and development associated with

Big-net timeline of EEW alert issuance at tA and gray zones

EEW have been carried out, and how EEW systems pres-where strong shaking may arrive at tS before tA. The verticalently function. We then show short-wavelength variation ofaxis is the time relative to an earthquake origin time, andthe horizontal axis the epicentral distance (D). Gray zones

ground motions within the typical station interval of a big-net

are illustrated for networks of different station spacing Δx =using data recorded by a dense local seismic network in

10, 20, 30, and 40 km. For example, for a network of Δx =Japan. However, it is not particularly meaningful to attempt

20 km, the gray zone radius is ~17 km from the epicenter,detailed modeling of varieties of ground motion within thewhere the ground shaking may arrive before an alert andstation interval for a big-net EEW operation, because theis likely to be stronger, causing more damage than outside

possible combinations of earthquake sources, paths of wave

of it.

propagation, and recipient sites are infinite. We emphasize(bottom)
Big-net station distributions: a. the station spacing in Japanthat in all circumstances, for recipients to benefit from EEW,

is ~20 km or less over the country. This implies that theseismic safety preparations must be implemented. Neces-

average gray zone radius is ~17 km from a hypocenter;sary preparations at sites do not diminish in importance afterb. the station spacing in the West Coast/USA is not homo-incremental improvements in station coverage and/or algo-geneous, i.e., it is ~10 km in the populated metropolitan

rithms in a big-net operation. Further, scientists and engi-

areas such as around Los Angeles, San Francisco Bay andneers involved in EEW projects should strive to publically

Seattle whereas it is larger in less populated areas.

disseminate how big-net EEW systems work, and also why,to achieve maximum benefit, these systems should always
be supplemented by preparations at recipients’ sites.

Published: 2018/10/10
https://doi.org/10.1186/s40645-018-0221-6― 88 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Redox-controlled mechanisms of C and H isotope fractionation between silicate melt and COH
fluid in the Earth’s interior
Mysen B
[Keywords] Fluid, Solubility, Structure, Spectroscopy, Redox, Stable isotopes

The behavior of COH fluids, their isotopes(hydrogen and carbon), and their interaction with magmatic liquids are at the core ofunderstanding formation and evolution of the
Earth. Experimental data are needed to aid
our understanding of how COH volatiles affectrock-forming processes in the Earth’s interior.
Here, I present a review of experimental data on
structure of fluids and melts and an assessmentof how structural factors govern hydrogen andcarbon isotope partitioning within and between
melts and fluids as a function of redox conditions, temperature, and pressure.
The solubility of individual COH components
in silicate melts can differ by several ordersof magnitude and ranges from several hundred ppm to several wt%. Silicate solubility in
fluid can reach several molecular at mantle
temperatures and pressures. Different solubility of oxidized and reduced C-bearing species in melts reflects different solution equilibria. These equilibria are
2CH4+Qn=2CH3−+H2O+Qn+1 and 2CO32−+H2O+2Qn+1=HCO3−+2Qn, under reducing and oxidizing conditions, respectively. In the Qn-notations, the superscript, n, denotes the number of bridging oxygen in the silicate species (Q-species).
The structural changes of carbon and silicate in magmatic systems (melts and fluids) with variable redox conditions
result in hydrogen and carbon isotope fractionation factors between melt, fluid, and crystalline materials that dependon redox conditions and can differ significantly from 1 even at magmatic temperatures. The ΔH of D/H fractionation
between aqueous fluid and magma in silicate–COH systems is between −5 and 25 kJ/mol depending on redox conditions. The ΔH values for 13C/12C fractionation factors are near −3.2 and 1 kJ/mol under oxidizing and reducing conditions, respectively. These differences are because energetics of O–D, O–H, O–13C, and O–12C bonding environments
are governed by different solution mechanisms in melts and fluids.
From the above data, it is suggested that (COH)-saturated partial melts in the upper mantle can have δD values
100%, or more, lighter than coexisting silicate-saturated fluid. This effect is greater under oxidizing than under reducing
conditions. Analogous relationships exist for 13C/12C. At magmatic temperatures in the Earth’s upper mantle, 13C/12C
of melt in equilibrium with COH-bearing mantle in the −7 to −30‰ range increases with temperature from about 40
to >100‰ and 80–120‰ under oxidizing and reducing conditions, respectively.

Published: 2018/9/1
https://doi.org/10.1186/s40645-018-0203-8― 89 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Nonlinear dynamical analysis of GNSS data: quantification, precursors and synchronization
Hobbs B, Ord A[Keywords] GNSS time series, Nonlinear analysis, Dynamical systems, Recurrence plots, Recurrence quantification
analysis (RQA), Cross and joint recurrence plots, Crustal deformation, Precursors, Synchronisation

The goal of any nonlinear dynamical analysis of a data series is to extract features of the
dynamics of the underlying physical and chemical processes that produce that spatial patternor time series; a by-product is to characterise
the signal in terms of quantitative measures. In
this paper, we briefly review the methodology
involved in nonlinear analysis and explore timeseries for GNSS crustal displacements with aview to constraining the dynamics of the underlying tectonic processes responsible for the
kinematics. We use recurrence plots and theirquantification to extract the invariant measuresof the tectonic system including the embedding
dimension, the maximum Lyapunov exponent
and the entropy and characterise the systemusing recurrence quantification analysis (RQA).

Synchronisation of GNSS data in New Zealand. Colored map is a joint
recurrence plot of detrended coordinate time series (E-W component) at
CNST (below) and KAIK (left) sites. Correlation concentrates along the
diagonal line 250-400 days before large slow slip events (~800, =2100,
and 3300 days), indicating synchronisation.

These measures are used to develop a data
model for some GNSS data sets in New Zealand. The resulting dynamical model is tested using nonlinear prediction
algorithms. The behaviours of some RQA measures are shown to act as precursors to major jumps in crustal displacement rate. We explore synchronisation using cross- and joint-recurrence analyses between stations and showthat generalised synchronisation occurs between GNSS time series separated by up to 600 km. Synchronisation
between stations begins up to 250 to 400 days before a large displacement event and decreases immediately before
the event. The results are used to speculate on the coupled processes that may be responsible for the tectonics ofthe observed crustal deformations and that are compatible with the results of nonlinear analysis. The overall aim is toplace constraints on the nature of the global attractor that describes plate motions on the Earth.

Published: 2018/7/23
https://doi.org/10.1186/s40645-018-0193-6― 90 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California:
insight into mélange origins and subduction-accretion processes
John Wakabayashi[Keywords] Ocean plate stratigraphy, Subduction complex evolution, Subduction megathrust slip accommodation,
tectonic and sedimentary mélanges

The transfer (accretion) of materials from a
subducting oceanic plate to a subduction-accretionary complex has produced rock assemblages recording the history of the subductedoceanic plate from formation to arrival at the
trench. These rock assemblages, comprisingoceanic igneous rocks progressively overlain
by pelagic sedimentary rocks (chert and/or
limestone) and trench-fill clastic sedimentaryrocks (mostly sandstone, shale/mudstone),have been called ocean plate stratigraphy

Cross sectional cartoon showing accretion of OPS and the connection(OPS). During accretion of OPS, megathrust

between this process and the rock assemblages found in subduction com-

slip is accommodated by imbricate faults andplexes, including different types of mélanges. This schematic also illus-

penetrative strain, shortening the unit and lead-trates that olistostromes of serpentinite and/or siliciclastic matrix comprise

ing to tectonic repetition of the OPS sequence,part of the clastic part of OPS.

whereas OPS accreted at different times are
separated by non-accretionary megathrust horizons. The Franciscan subduction complex of California accreted episodically over a period of over 150 million years and incorporated OPS units with a variety of characteristics separated by non-accretionary megathrust horizons. Most Franciscan OPS comprises MORB (mid-ocean-ridge basalt)
progressively overlain by chert and trench-fill clastic sedimentary rocks that are composed of variable proportions ofturbidites and siliciclastic and serpentinite-matrix olistostromes (sedimentary mélanges). Volumetrically, the trenchfill component predominates in most Franciscan OPS, but some units have a significant component of igneous andpelagic rocks. Ocean island basalt (OIB) overlain by limestone is less common than MORB-chert assemblages, as
are abyssal serpentinized peridotite slabs. The earliest accreted OPS comprises metabasite of supra-subduction zone
affinity imbricated with smaller amounts of metaultramafic rocks and metachert, but lacking a clastic component. Most
deformation of Franciscan OPS is localized along discrete faults rather than being distributed in the form of penetrative
strain. This deformation locally results in block-in-matrix tectonic mélanges, in contrast to the sedimentary mélanges
making up part of the clastic OPS component. Such tectonic mélanges may include blocks and matrix derived from theolistostromes. Franciscan subduction and OPS accretion initiated in island arc crust at about 165–170 Ma, after which
MORB and OIB were subducted and accreted following a long (tens of mega-ampere) gap with little or no accretion.
Following subduction initiation, a ridge crest approached the trench but probably went dormant prior to its subduction(120–125 Ma), after which the subducted oceanic crust became progressively older until about 95 Ma. From 95 Ma,
the age of subducted oceanic crust decreased progressively until arrival of the Pacific-Farallon spreading center led
to termination of subduction and conversion to a transform plate boundary.

Published: 2017/7/7
https://doi.org/10.1186/s40645-017-0132-y― 91 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes
Hasegawa A, Nakajima J[Keywords] Internal slab structure, slab metamorphism, dehydration-related embrittlement, intermediate-depth
earthquake, intraslab earthquake, earthquake generation mechanism, subduction zone

We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab
metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events forma double seismic zone in the depth range of c. 40–180 km,
which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial
distributions of these events and a close relationship with slab
metamorphism. Pressure–temperature paths of the crust for coldslabs encounter facies boundaries with large H2O production
rates and positive total volume change, which are expected tocause highly active seismicity near the facies boundaries. A beltof upper-plane seismicity in the crust nearly parallel to 80–90
km depth contours of the slab surface has been detected in
the cold Pacific slab beneath eastern Japan, and is probably
caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists
down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at thisFig. 1 (a) P–T paths of the subducting crust for six subduction zones. Shading shows maximum H2O contents
in wt%. (b) Accumulated dehydration-derived H2O content in wt%, (c) rate of H2O production and (d) total

depth. Similar low-velocity subducting crust closely related withsystem (solid + H2O) volume for Hokkaido (blue lines)

intraslab seismicity has been detected in several other subduc-

as a representative cold slab, and for Kii (red lines) astion zones. Seismic tomography studies in NE Japan and north-a representative warm slab. In (c), Kii is scaled by aern Chile also revealed the presence of a P-wave low-velocity

factor of 10. (e) Frequency of upper-plane earthquakes

layer along the lower plane of a double seismic zone. However,

beneath central Hokkaido as a function of depth.

in contrast to predictions based on the serpentinized mantle,
S-wave velocity along this layer is not low. Seismic anisotropy
and pore aspect ratio may play a role in generating this uniquestructure. Although further validation is required, observationsof these distinct low P-wave velocities along the lower seismic
plane suggest the presence of hydrated rocks or fluids withinthat layer. These observations support the hypothesis that dehy-

Fig. 2 (a) S-wave velocity distribution and (b) earth-dration-derived H2O causes intermediate-depth intraslab earth-quake hypocenters within the crust of the Pacific slab. A

quakes. However, it is possible that dual mechanisms generatethese earthquakes; the initiation of earthquake rupture may becaused by local excess pore pressure from H2O, and subsequent ruptures may propagate through thermal shear instability.

belt of upper-plane seismicity is shown in pink. Broken
black curves denote iso-depth contours of the upper
plate surface. The slab–slab contact zone between the
Pacific and Philippine Sea slabs is enclosed by two
green broken curves.

In either case, slab-derived H2O plays an important role in generating intermediate-depth events.
Published: 2017/4/10
https://doi.org/10.1186/s40645-017-0126-9― 92 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Imaging in 3D under pressure: a decade of high-pressure X-ray microtomography development
at GSECARS
Yu T, Wang Y, Rivers M L[Keywords] High pressure, Tomography, Synchrotron, Density, Rotation, Shear, Non-crystalline, Elasticity

The high-pressure X-ray microtomography(HPXMT) apparatus has been operating at
the GeoSoilEnviroCARS (GSECARS) bending magnet beamline at the Advanced Photon
Source since 2005. By combining the powerfulsynchrotron X-ray source and fast switching
between white (for X-ray diffraction) and monochromatic (for absorption imaging) modes, thistechnique provides the high-pressure community with a unique opportunity to image thethree-dimensional volume, texture, and microstructure of materials under high pressure andtemperature. The ability to shear the sample
with unlimited strain by twisting the two opposedanvils in the apparatus allows shear deformation studies under extreme pressure and temperature to be performed. HPXMT is a powerfultool for studying the physical properties of both
crystalline and non-crystalline materials underhigh pressure and high temperature. Over the
past 10 years, continuous effort has been put
into technical development, modifications toimprove the overall performance, and additional
probing techniques to meet users’ needs. Here,
we present an up-to-date report on the HPXMT

Evolution of FeS melt distribution in the olivine matrix by shear deformation.

system, a brief review of some of its many exciting scientific applications, and a discussion of
future developments.

Published: 2016/6/8
https://doi.org/10.1186/s40645-016-0093-6― 93 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Philippine Sea Plate inception, evolution and consumption with special emphasis on the earlystages of Izu-Bonin-Mariana subduction
Lallemand S[Keywords] Philippine Sea Plate, Izu-Bonin-Mariana, subduction initiation, boninite, fore-arc basalt, serpentinite mud
volcano, back-arc basin, transform fault, arc terrane, plume-ridge interaction

We compiled the most relevant data acquired throughout the Philippine Sea Plate (PSP) from the early expeditions to the most recent. We also analyzed the various
explanatory models in light of this updated dataset. The
following main conclusions are discussed in this study.
(1) The Izanagi slab detachment beneath the East
Asia margin around 60–55 Ma likely triggered the OkiDaito plume occurrence, Mesozoic proto-PSP splitting,shortening and then failure across the paleo-transformboundary between the proto-PSP and the Pacific Plate,
Izu-Bonin-Mariana subduction initiation and ultimately
PSP inception. (2) The initial splitting phase of the composite proto-PSP under the plume influence at ~54–48
Ma led to the formation of the long-lived West Philippine
Basin and short-lived oceanic basins, part of whose
crust has been ambiguously called “fore-arc basalts”(FABs). (3) Shortening across the paleo-transformboundary evolved into thrusting within the Pacific Plate
at ~52–50 Ma, allowing it to subduct beneath the newly
formed PSP, which was composed of an alternance ofthick Mesozoic terranes and thin oceanic lithosphere.
(4) The first magmas rising from the shallow mantle
corner, after being hydrated by the subducting Pacificcrust beneath the young oceanic crust near the upper
plate spreading centers at ~49–48 Ma were boninites.
Both the so-called FABs and the boninites formed at asignificant distance from the incipient trench, not in afore-arc position as previously claimed. The magmas
erupted for 15 m.y. in some places, probably near the

Schematic tectono-magmatic model of IBM subduction initiationand early evolution. Special emphasis has been done on the geodynamic context of various magma1 eruptions. The white lines instage “40 Ma - present” represent the former positions of plateintersections between back-arc spreading centers andboundaries or the base of the upper plate in stage “45-40 Ma”.

the arc. (5) As the Pacific crust reached greater depths

TF = transform fault, PAC = Pacific, FAB = Forearc basalts

and the oceanic basins cooled and thickened at ~44–
45 Ma, the composition of the lavas evolved into high-Mg andesites and then arc tholeiites and calc-alkaline andesites.
(6) Tectonic erosion processes removed about 150–200 km of frontal margin during the Neogene, consuming mostor all of the Pacific ophiolite initially accreted to the PSP. The result was exposure of the FABs, boninites, and earlyvolcanics that are near the trench today. (7) Serpentinite mud volcanoes observed in the Mariana fore-arc may haveformed above the remnants of the paleo-transform boundary between the proto-PSP and the Pacific Plate.
Published: 2016/5/12
https://doi.org/10.1186/s40645-016-0085-6― 94 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Mantle hydration and Cl-rich fluids in the subduction forearc
Reynard B[Keywords] Subduction, Fluids, Forearc mantle, Salinity, Chlorine

In the forearc region, aqueous fluids are
released from the subducting slab at a ratedepending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plateinterface or the Moho of the overriding plate.
Channeling of fluids along the plate interface
and Moho may result in fluid overpressure in
the oceanic crust, precipitation of quartz fromfluids, and low Poisson ratio areas associatedwith tremors. Above the subducting plate, theforearc mantle wedge is the place of intense
reactions between dehydration fluids from thesubducting slab and ultramafic rocks leading
to extensive serpentinization. The plate inter-

Potential location of high-salinity fluids in the forearc mantle and pathwaysof mixing with hotsprings and the volcanic arc. Magnetotelluric profiles in
the Cascadia subduction (Wannamaker, et al. 2014) are shown on theright and are interpreted on the left. The southernmost section shows theface is mechanically decoupled, most likely inhighest conductivity in the forearc (green ellipse) that is interpreted as up

relation to serpentinization, thereby isolatingto 1 m NaCl fluids using diagrams in Fig. 2. Lower forearc conductivities

the forearc mantle wedge from convection as(green ellipses) on the other two sections indicate dilution by more thana cold, potentially serpentinized and buoyant,

one order of magnitude by low-salinity dehydration fluids from the slab or abody. Geophysical studies are unique probes

decrease by more than one order of magnitude of the fluid fraction. This isto the interactions between fluids and rocks inthe forearc mantle, and experimental constrains
on rock properties allow inferring fluid migration

attributed drainage to shallow aquifers above the forearc region (e. g., theWillamette basin in Oregon, WB) or to the volcanic arc (VA) region (green
arrows). High-conductivity regions further east are ascribed to melt-richregions under the volcanic arc (red ellipses)and fluid-rock reactions from geophysical data.
Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little
serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amountof water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data frompetrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis
and interpretation of seismic data. Electrical conductivity increases with increasing fluid content and temperature of
the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not
only with the thermal state of the subduction zone, but also with time for a given thermal state through variations of
fluid salinity. High-Cl fluids produced by serpentinization can mix with the source rocks of the volcanic arc and explain
geochemical signatures of primitive magma inclusions. Signature of deep high-Cl fluids was also identified in forearc
hot springs. These observations suggest the existence of fluid circulations between the forearc mantle and the hotspring hydrothermal system or the volcanic arc. Such circulations are also evidenced by recent magnetotelluric profiles.

Published: 2016/4/28
https://doi.org/10.1186/s40645-016-0090-9― 95 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Iron snow, crystal floats, and inner-core growth: modes of core solidification and implications for
dynamos in terrestrial planets and moons
Breuer D, Rueckriemen T, Spohn T[Keywords] Core crystallization, Dynamo generation, Iron snow, Terrestrial planets, Thermal evolution

Recent planetary space missions, new experimental
data, and advanced numerical techniques have helped
to improve our understanding of the deep interiorsof the terrestrial planets and moons. In the present
review, we summarize recent insights into the stateand composition of their iron (Fe)-rich cores, as well
as recent findings about the magnetic field evolutionof Mercury, the Moon, Mars, and Ganymede. Crystallizing processes in iron-rich cores that differ from theclassical Earth case (i.e., Fe snow and iron sulfide(FeS) crystallization) have been identified and foundto be important in the cores of terrestrial bodies. The
Fe snow regime occurs at pressures lower than thatin the Earth’s core on the iron-rich side of the eutectic, where iron freezes first close to the core–mantle
boundary rather than in the center. FeS crystallization,
instead, occurs on the sulfur-rich side of the eutectic.
Depending on the core temperature profile and thepressure range considered, FeS crystallizes either inthe core center or close to the core–mantle boundary.
The consequences of the various crystallizing mechanisms for core dynamics and magnetic field generation
are discussed. For the Moon, revised paleomagnetic
data obtained with advanced techniques suggest apeculiar history of its internal dynamo, with an earlystrong field persisting between 4.25 and 3.5 Ga, andsubsequently a much weaker field. In addition, thelong-lasting dynamo and the possible presence of an
inner core, as inferred from a revised interpretation of
Apollo seismic data, suggest core crystallization as a
viable process of magnetic field generation for a substantial period during lunar evolution. The present-day
magnetic fields of Mercury and Ganymede (if theyoccur on the iron-rich side of the Fe–FeS eutectic)
and the related dynamo action are likely generated in
the Fe snow regime and seem to be recent features.
An earlier dynamo in Mercury would have been powered differently. For Mercury, MESSENGER data further suggest core formation under reducing conditions
that may have resulted in an Fe–S–Si composition,

Crystallization scenarios in the Fe–FeS system. Crystallization scenarios in the Fe–FeS system. a Earth-like, Fe-rich inner core grows
from the center. Sulfur is enriched in the outer core and drives
chemical convection. b Iron snow forms at the CMB, sinks, andremelts at depth and drives chemical convection. The stable snow
zone grows in time. When it reaches the center, an inner solidcore will form. c Floating FeS crystals form a stable zone growing
toward the CMB where eventually a solid FeS layer will form. The
fluid below is enriched in iron and unstable to convection. d A solid
FeS layer grows from the CMB. Expulsion of Fe results in chemical
convection in the fluid below as in (c). e FeS crystals rise from thecenter and remelts at lower depths. The liquid above the FeS zone
is convectively unstable. When the FeS crystal zone reaches the
CMB, a solid FeS layer will form. f Fe3S snow forms at the CMB
and the chemically unstable snow zone grows until it comprises theentire core where a solid Fe3S inner core will form. The layer below
is chemically homogeneous but may convect thermally. g A solid
Fe3S inner core grows with time without the release of chemical
buoyancy to the outer core and convection above. Red, green, andblue dots indicate solid iron, solid FeS, and Fe3S, respectively.
Short dashes show the direction of sinking or rising. Red solidlines are the core temperature, blue dashed lines the core melting temperature, and black solid lines the concentration of sulfur,
respectively. Solid arrows indicate chemical and dashed arrows
thermal convection, respectively. For further explanation, see text.

further complicating the core crystallization process.
Mars, with its early and strong paleo-field, likely has
not yet started to freeze out an inner iron core.

Published: 2015/11/16
https://doi.org/10.1186/s40645-015-0069-y― 96 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Liquid Sodium Models of the Earth’s Core
Adams M M, Stone D R, Zimmerman D S, Lathrop D P[Keywords] Magnetic dynamos, Fluid experiments, Geodynamo, Magnetic induction, Zonal flows, Turbulence,
Experimental fluid dynamos, Spherical Couette flow

Our understanding of the dynamics of the Earth’s core canbe advanced by a combination of observation, experiments,and simulations. A crucial aspect of the core is the interplay
between the flow of the conducting liquid and the magnetic
field this flow sustains via dynamo action. This non-linear
interaction, and the presence of turbulence in the flow, precludes direct numerical simulation of the system with realistic
turbulence. Thus, in addition to simulations and observations(both seismological and geomagnetic), experiments can contribute insight into the core dynamics. Liquid sodium laboratory experiments can serve as models of the Earth’s corewith the key ingredients of conducting fluid, turbulent flow,
and overall rotation, and can also approximate the geometryof the core. By accessing regions of parameter space inaccessible to numerical studies, experiments can benchmark
simulations and reveal phenomena relevant to the Earth’s
core and other planetary cores. This review focuses on the
Rendering of the 3 m experiment. The inner sphere and theparticular contribution of liquid sodium spherical Couetteouter spherical shell can be driven independently by theirdevices to this subject matter.

two respective motors (top). Liquid sodium serves as theworking fluid for hydromagnetic experiments

Published: 2015/9/17
https://doi.org/10.1186/s40645-015-0058-1― 97 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos
Amit H, Choblet G, Olson P, Monteux J, Deschamps F, Langlais B, Tobie G[Keywords] Magnetic field, Dynamo, Core-mantle boundary, Heat flux

Mantle control on planetary dynamos is often
studied by imposing heterogeneous core-mantle boundary (CMB) heat flux patterns on theouter boundary of numerical dynamo simulations. These patterns typically enter two maincategories: Either they are proportional to seismic tomography models of Earth’s lowermost
mantle to simulate realistic conditions, or they
are represented by single spherical harmonics
for fundamental physical understanding. However, in reality the dynamics in the lower mantle is much more complicated and these CMB
heat flux models are most likely oversimplified.

Top: Geomagnetic reversal frequency (yellow and barcode below) basedon the Geomagnetic Polarity Time Scale (GPTS) database vs. reversal
frequency in dynamo models with time-dependent CMB heat flux (black

Here we term alternative any CMB heat flux pat-pluses) and fixed present-day tomographic pattern (red crosses). The Cre-tern imposed on numerical dynamos that does

taceous Normal Superchron (CNS), Kiaman Reversed Superchron (KRS)

not fall into these two categories, and insteadand Moyero Reversed Superchron (MRS) are grey shaded.

attempts to account for additional complexity
in the lower mantle. We review papers that

Bottom: Polarity bias, i.e. the difference between time spent in normal andreversed polarities normalized by their sum.

attempted to explain various dynamo-related
observations by imposing alternative CMB heat flux patterns on their dynamo models. For present-day Earth, the alternative patterns reflect non-thermal contributions to seismic anomalies or sharp features not resolved by global tomography models. Time-dependent mantle convection is invoked for capturing past conditions on Earth’s CMB. For Mars,
alternative patterns account for localized heating by a giant impact or a mantle plume. Recovered geodynamo-related
observations include persistent morphological features of present-day core convection and the geomagnetic field aswell as the variability in the geomagnetic reversal frequency over the past several hundred Myr. On Mars the models
aim at explaining the demise of the paleodynamo or the hemispheric crustal magnetic dichotomy. We report the main
results of these studies, discuss their geophysical implications, and speculate on some future prospects.

Published: 2015/9/9
https://doi.org/10.1186/s40645-015-0056-3― 98 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison with seismic models
Antonangeli D, Ohtani E[Keywords] Sound velocity measurements, High pressure, hcp-Fe, Extrapolation schemes, Earth’s inner core,
Comparison with seismic models

Determining the sound velocity of iron under
extreme thermodynamic conditions is essential
for a proper interpretation of seismic observations of the Earth’s core but is experimentallychallenging. Here, we review techniques andmethodologies used to measure sound velocities in metals at megabar pressures, withspecific focus on the compressional soundvelocity of hexagonal close-packed iron. A critical comparison of literature results, coherently
analyzed using consistent metrology (pressure
scale, equation of state), allows us to propose
reference relations for the pressure and density dependence of the compressional velocityof hexagonal close-packed iron at ambient temperature. This provides a key base line uponwhich to add complexity, including high-temperature effects, pre-melting effects, effects of

Figure 1: Various previous experimental data on sound velocity and density of hcp-Fe are corrected based on the same pressure scale and theequation of state of hcp-Fe. Most of previous data are consistent witheach other.

nickel and/or light element incorporation, necessary for an accurate comparison with seismic
models, and ultimately to constrain Earth’s innercore composition.

Figure 2: Compressional sound velocity as a function of density under
static compression at 300 K is compared with the shock wave data along
Hugoniot. The temperature effect on the Birch’s law is clearly observedin this figure.

Published: 2015/3/13
https://doi.org/10.1186/s40645-015-0034-9― 99 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms
Ujiie K, Kimura G[Keywords] Subduction earthquake, Accretionary prism, Fault rock, NanTroSEIZE

Subduction earthquakes on plate-boundary
megathrusts accommodate most of the global
seismic moment release, frequently resulting
in devastating damage by ground shaking andtsunamis. As many earthquakes occur in deepsea regions, the dynamics of earthquake faulting in subduction zones is poorly understood.
However, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone
Experiment (NanTroSEIZE) and fault rock studies in accretionary prisms exhumed from source
depths of subduction earthquakes have greatly
improved our understanding of earthquake
faulting in subduction zones. Here, we review
key advances that have been made over theConcept of earthquake faulting in subduction zones shown in schematic
profile of the Nankai accretionary prism.

last decade in the studies of fault rocks and inlaboratory experiments using fault zone materials, with a particular focus on the Nankai Trough subduction zone andits on-land analog, the Shimanto accretionary complex in Japan. New insights into earthquake faulting in subduction
zones are summarized in terms of the following: (1) the occurrence of seismic slip along velocity-strengthening materials both at shallow and deep depths; (2) dynamic weakening of faults by melt lubrication and fluidization, and possible
factors controlling coseismic deformation mechanisms; (3) fluid-rock interactions and mineralogical and geochemicalchanges during earthquakes; and (4) geological and experimental aspects of slow earthquakes.

Published: 2014/6/3
https://doi.org/10.1186/2197-4284-1-7― 100 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Solid earth sciences

Water-melt interaction in hydrous magmatic systems at high temperature and pressure
Bjorn Mysen[Keywords] Hydrous magma, Aqueous fluid, Melt structure, Viscosity, Isotope partitioning, Partial melting, Water
solubility, Silicate solubility, Glass transition, Solution mechanism

Experimental data on the structure and propertiesof melts and fluids relevant to water-melt interaction
in hydrous magmatic systems in the Earth’s interior
have been reviewed. Complex relationships between
water solubility in melts and their bulk composition [Al/Si-ratio, metal oxide/(Al + Si) and electron propertiesof metal cations] explain why water solubility in felsicmagmas such as those of rhyolite and andesite composition is significantly greater than the water solubility
in basalt melts. The silicate solubility in aqueous fluid isalso significantly dependent on composition with metaloxide/(Al + Si) and electron properties of the metal cations, the dominant variables. Hydrogen bonding is notimportant in hydrous fluids and melts at temperatures
above 500°C to 550°C and does not, therefore, playa role in hydrous magmatic systems. The properties
of hydrous melts and aqueous solutions are governedby how the silicate speciation (Qn species, where n is
the number of bridging oxygen in an individual species)
varies with bulk composition, silicate composition, temperature, and pressure. The reactions that describe theinteractions are similar in melts, fluids, and supercritical fluids. The degree of melt polymerization caused by

Schematic representation of the concept of bridging (BO) andnonbridging (NBO) oxygen

dissolved water varies with melt composition and total
water content. Silicate- and alkali-rich felsic magmatic
melts are more sensitive to water content than more
mafic magmas. Transport and configurational properties of hydrous magmatic melts can be modeled withthe aid of the Qn speciation variations. Liquidus andmelting phase relations of hydrous systems also canbe described in such terms, as can minor and traceelement partition coefficients. Stable isotope fractionation (e.g., D/H) can also be rationalized in this manner.
Critical to these latter observations is the high silicate
concentration in aqueous fluids. These components
can enhance solubility of minor and trace elements

Degree of silicate polymerization, NBO/T. In silicate in hydrous

by orders of magnitude and change the speciation ofmelts, silicate-saturated aqueous fluid, and supercritical fluid in a

H and D complexes so that their fractionation factors

hydrous Na-aluminosilicate systemchange quite significantly. Data from pure silicate-H2O
systems cannot be employed for these purposes.

Published: 2014/4/22
https://doi.org/10.1186/2197-4284-1-4― 101 ―

Review
Interdisciplinary researchProgress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Identifying key processes and sectors in the interaction between climate and socio-economic
systems: a review toward integrating Earth–human systems
Tachiiri K, Su X, Matsumoto K[Keywords] Earth system model, Integrated assessment model, Socio-economic system, Climate system, HumansystemFor the purpose of identifying the key processes and sectors involved in the interaction
between Earth and socio-economic systems,
we review existing studies on those processes/
sectors through which the climate impacts
socio-economic systems, which then in turnaffect the climate. For each process/sector, we
review the direct physical and ecological impacts
and, if available, the impact on the economy
and greenhouse gas (GHG) emissions. Basedon this review, land sector is identified as theprocess with the most significant impact on
GHG emissions, while labor productivity has thelargest impact on the gross domestic productConceptual diagram of the Earth-human (socio-economic) system inter-(GDP). On the other hand, the energy sector,

action.

due to the increase in the demand for cooling,
will have increased GHG emissions. Water resources, sea level rise, natural disasters, ecosystem services, and diseases also show the potential to have a significant influence on GHG emissions and GDP, although for most of these,a large effect was reported only by a limited number of studies. As a result, more studies are required to verify theirinfluence in terms of feedbacks to the climate. In addition, although the economic damage arising from migration andconflict is uncertain, they should be treated as potentially damaging processes.

Published: 2021/4/8
https://doi.org/10.1186/s40645-021-00418-7― 104 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Coupling library Jcup3: its philosophy and application
Arakawa T, Inoue T, Yashiro H, Satoh M[Keywords] Earth system modeling, Coupler, Coupled simulation

In this paper, we describe the design of thecoupling library, Jcup, and report its various
applications, including the coupling between
global atmospheric and oceanic models of different grid systems. Jcup is a software library
mainly focused on weather/climate models andwas developed for coupling the components ofvarious models. Jcup has the flexibility to be
applied to an unspecified number of components of earth system models. To achieve ahigh level of safety and versatility, we classified
the processes of the general coupling software

Data exchange diagram. The gray circles represent masked value. There-

into processes that change the value of the data

fore, only the grid point value indicated by the blue circle is passed fromand those that do not and placed the former

Component A to Component B.

outside of the program and under the controlof the user. Consequently, Jcup exhibits two features: (1) the correspondence relationship between grid indexes isused as input information, and (2) the user can implement an arbitrary interpolation code. Jcup was applied to atmosphere-ocean coupling, IO component coupling, and the coupling between the seismic model and structure model,
and the validity and usefulness of the design were demonstrated.

Published: 2020/2/6
https://doi.org/10.1186/s40645-019-0320-z― 105 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Morphometric measurements of bedrock rivers at different spatial scales and applications togeomorphological heritage research
Gomez-Heras M, Ortega-Becerril JA, Garrote J, Fort R, Lopez-Gonzalez L[Keywords] Bedrock rivers, Geomorphological heritage, Non-destructive techniques, Digital elevation models, LiDAR,
SfM, Photogrammetry, Microroughness

Morphometric characterisation is particularly relevant in the study of geomorphological
heritage. 3D modelling techniques have been
proven as very useful tools to recognise, characterise and valorise geomorphosites. Bedrock
rivers account for one of the most outstanding aspects within geomorphological heritage
due to the amount of distinctive and attractive
geomorphological features associated to themand the high preservation of sculpted forms.
Digital elevation models (DEMs) have made it(a) Example of DEM for different scales of morphometric measurements

increasingly possible to establish accurate mor-in bedrock rivers, (b) Large-scale airborne scan, (c) mesoscale SfM, (d)phometric indices and establish clearer connec-

microscale rugosimetertions between forms and processes. This paper
reviews different methodologies to obtain DEMs on bedrock rivers. This review goes from DEM analysis at multiple
spatial scales to introduce optical microrugosimeter as the latest technical development to facilitate micromorphometricanalysis. Micromorphometric analysis opens the scope for improving the knowledge we have on trans-scale issues in
bedrock rivers. Micromorphometric analysis also opens a new layer of information that enriches the public’s valuationof geodiversity of geomorphosites by increasing its didactic and interpretative potential.

Published: 2019/3/25
https://doi.org/10.1186/s40645-019-0275-0― 106 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary researchNorthern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change
in the twenty-first century
Pavel Groisman et al.
[Keywords] Environmental Changes, Northern Eurasia, Ecosystems dynamics, Terrestrial water cycle, Cryosphereretreat, Extreme and inclement environmental conditions, Sustainable development, Land-cover and land-use change,
Integrated assessment models for decision-makers

During the past several decades, the Earthsystem has changed significantly, especiallyacross Northern Eurasia. Changes in thesocio-economic conditions of the larger countries in the region have also resulted in a variety of regional environmental changes that
can have global consequences. The Northern Eurasia Future Initiative (NEFI) has been
designed as an essential continuation of theNorthern Eurasia Earth Science Partnership
Initiative (NEESPI), which was launched in
2004. NEESPI sought to elucidate all aspects ofongoing environmental change, to inform societies and, thus, to better prepare societies for

Changes in sown areas across the former Soviet Union (Russia, Ukraine,and Kazakhstan) from 1990 to 2013. Areas of abandoned sown areas

future developments. A key principle of NEFI isfor this period are 40 Mha in Russia (Rosstat 2016), 5.4 Mha in Ukrainethat these developments must now be secured(Ukrstat 2014), and 13 Mha in Kazakhstan (Kazstat 2014).

through science-based strategies co-designedwith regional decision-makers to lead their societies to prosperity in the face of environmental and institutional challenges. NEESPI scientific research, data, and models have created a solid knowledge base to support the NEFI
program. This paper presents the NEFI research vision consensus based on that knowledge. It provides the reader
with samples of recent accomplishments in regional studies and formulates new NEFI science questions. To addressthese questions, nine research foci are identified and their selections are briefly justified. These foci include warmingof the Arctic; changing frequency, pattern, and intensity of extreme and inclement environmental conditions; retreatof the cryosphere; changes in terrestrial water cycles; changes in the biosphere; pressures on land use; changes ininfrastructure; societal actions in response to environmental change; and quantification of Northern Eurasia’s role in
the global Earth system. Powerful feedbacks between the Earth and human systems in Northern Eurasia (e.g., megafires, droughts, depletion of the cryosphere essential for water supply, retreat of sea ice) result from past and current
human activities (e.g., large-scale water withdrawals, land use, and governance change) and potentially restrict orprovide new opportunities for future human activities. Therefore, we propose that integrated assessment models areneeded as the final stage of global change assessment. The overarching goal of this NEFI modeling effort will enableevaluation of economic decisions in response to changing environmental conditions and justification of mitigation andadaptation efforts.

Published: 2017/12/27
https://doi.org/10.1186/s40645-017-0154-5― 107 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Cenozoic sedimentary records of climate-tectonic coupling in the Western Himalaya
Clift P D
[Keywords] Monsoon, Climate-tectonic, Himalaya, Erosion, Exhumation, Arabian Sea, Foreland basin, Provenance,
Geochemistry, Cenozoic, Weathering

Sedimentary archives in the Himalayan foreland basin and Indus submarine fan provide themost detailed records of how changing monsoon strength may have affected erosion andthe development of tectonic structures in thewestern Himalaya during the Neogene. Muscovite Ar-Ar ages show that fast exhumation of
the Greater Himalaya was earlier in the west
(20–35 Ma) than in the central Himalaya (10–25Ma), probably driven by progressive lithosphericslab tearing that caused both rock uplift and an

The correlation between the uplift of the Himalaya-Tibetan Plateau andthe Asian monsoon

intensified summer monsoon to start earlier inthe western Himalaya. Rates of exhumation reduced after ~17 Ma as uplift also slowed, apparently unrelated to climatechange. However, further reduction at 6–8 Ma coincided with a time of weakening summer rains, as shown by carbon
isotope data from the foreland and hematite-goethite records from ODP Site 730 on the Oman margin. Coming at atime of stronger winds, this drying was linked to global climatic cooling. Weakening of Late Miocene monsoon rains
coincided with a southward migration of the ITCZ and faster erosion of the Lesser rather than Greater Himalaya.
Unroofing of the Inner Lesser Himalaya, starting after 9 Ma, followed as a consequence of duplex formation enabled
by focused erosion, although widespread exposure of that range was delayed until after 6 Ma. Inner Lesser Himalayan
exposure, combined with unroofing of the Nanga Parbat Massif, caused a decrease in average εNd values of Indus
River sediment after 5 Ma, rather than large-scale drainage capture.

Published: 2017/12/14
https://doi.org/10.1186/s40645-017-0151-8― 108 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Transitional changes in microfossil assemblages in the Japan Sea from the Late Pliocene to
Early Pleistocene related to global climatic and local tectonic events
Itaki T
[Keywords] Radiolaria, Diatom, Calcareous nannofossil, Foraminifera, Ostracoda, Productivity, Paleoceanography,
Northern Hemisphere glaciation, Tectonics, Tsushima Warm Current

Many micropaleontological studies basedon data from on-land sections, oil wells, anddeep-sea drilling cores have provided important information about environmental changes
in the Japan Sea that are related to the global
climate and the local tectonics of the JapaneseIslands. Here, major changes in the microfossil
assemblages during the Late Pliocene to Early
Pleistocene are reviewed. Late Pliocene (3.5–
2.7 Ma) surface-water assemblages were characterized mainly by cold–temperate planktonic
flora and fauna (nannofossils, diatoms, radiolarians, and planktonic foraminifera), suggestingthat nutrient-rich North Pacific surface waters
entered the Japan Sea via northern straits. The
common occurrence of Pacific-type deep-water

Schematic maps showing paleogeographic changes in the Japan Sea
during three stages. Solid arrows show major inflows of oceanic water,and dashed arrows indicate restricted inflows.

radiolarians during this period also suggeststhat deep water from the North Pacific entered the Japan Sea via the northern straits, indicating a sill depth >500 m.
A weak warm-water influence is recognized along the Japanese coast, suggesting a small inflow of warm water via
a southern strait. Nannofossil and sublittoral ostracod assemblages record an abrupt cooling event at 2.75 Ma that
correlates with the onset of the Northern Hemisphere glaciation. Subsequently, cold intermediate- and deep-water
assemblages of ostracods and radiolarians increased in abundance, suggesting active ventilation and the formationof the Japan Sea Proper Water, associated with a strengthened winter monsoon. Pacific-type deep-water radiolarians
also disappeared around 2.75 Ma, which is attributed to the intermittent occurrence of deep anoxic environments
and limited migration from the North Pacific, resulting from the near-closure or shallowing of the northern strait bya eustatic fall in sea level and tectonic uplift of northeastern Japan. A notable reduction in primary productivity from
2.3 to 1.3 Ma also suggests that the nutrient supply from the North Pacific was restricted by the near-closure of thenorthern strait. An increase in the abundance of subtropical surface fauna suggests that the inflow of the Tsushima
Warm Current into the Japan Sea via a southern strait began at 1.7 Ma. The opening of the southern strait may haveoccurred after the subsidence of southwestern Japan.

Published: 2016/5/5
https://doi.org/10.1186/s40645-016-0087-4― 109 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Evolution and variability of the Asian monsoon and its potential linkage with uplift of theHimalaya and Tibetan Plateau
Tada R, Zheng H, Clift P D[Keywords] East Asian summer monsoon, East Asian winter monsoon, Indian summer monsoon, Himalaya, Tibetan
Plateau, Chinese Loess Plateau, Climate model, Tectonic–climate linkage, Westerly jet, Desertification

In the densely populated region of East Asia,
it is important to know the mechanism, scale,and frequency of heavy precipitation brought
about during the monsoons and typhoons.
However, observational data, which cover only
several decades, are insufficient to examine thelong-term trend of extreme precipitation and its
background mechanism. In humid areas, thetransport flux of a suspended detrital material
through a river system is known to have an
empirical power relationship with precipitation.
Thus, the sedimentation flux of a fine detritalmaterial could potentially be used as a proxy forreconstructing past heavy precipitation events.

Evolution of Asian monsoons, desertification, HTP uplift, and their rela-

To test the idea that the sedimentation flux oftion with global changes during Cenozoic. Temporal changes of a δ18O

detrital materials records past heavy precipitation events (e.g., typhoons), we focused on
the detrital flux estimated from the annuallyof benthic foraminifera (modified from Zachos et al. 2001) and b pCO2
(modified from Zhang et al. 2013) are compared with temporal evolutionof c Asian monsoons, d desertification, e HTP uplift, and f associatedtectonic events. In c and e, gray bars represent weak phases and black

laminated sediment of Lake Suigetsu, central

bars represent strong phases. In d, JuB and TaB indicate Jungger BasinJapan, which is capable of accurately correlat-

and Tarim Basin, respectively.

ing the age of detrital flux with the precipitation
record. We first established a precise age model (error within ±1 year in average) beginning in 1920 A.D. on the basisof varve counting fine-tuned by correlation between event layers with historical floods. The flux of the detrital material(g/cm2/year) was estimated on the basis of Al2O3 content (wt%), dry bulk density (g/cm3), and sedimentation rate (cm/year) calculated from the age model. The detrital flux of background sedimentation showed a weak positive correlation
with annual and monthly (June and September) precipitation excluding heavy precipitation that exceeded 100 mm/day.
Furthermore, the thickness of instantaneous event layers, which corresponds to several maxima of detrital flux and iscorrelated with floods that occurred mainly during typhoons, showed a positive relationship with the total amount ofprecipitation that caused a flood event. This result suggests that the detrital flux maxima (deposition of event layers)
record past extreme precipitation events that were likely associated with typhoons that hit the middle part of Honshu
Island. Based on this result, the record of typhoon-caused flood events can go back to older period (e.g., last glacial
period) on the basis of the occurrence, and thickness, or mass flux of event layers using long sediment cores from
Lake Suigetsu.

Published: 2016/2/9
https://doi.org/10.1186/s40645-016-0080-y― 110 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Geochemical approaches to the quantification of dispersed volcanic ash in marine sediment
Scudder R P, Murray R W, Schindlbeck J C, Kutterolf S, Hauff F, Underwood M B, Gwizd S, Lauzon R,
McKinley C C[Keywords] Dispersed ash, Caribbean Sea, Equatorial Pacific Ocean, Northwest Pacific Ocean, Ash layers, Volcanic
eruptions, DSDP, ODP, IODP

Volcanic ash has long been recognized inmarine sediment, and given the prevalence of
oceanic and continental arc volcanism aroundthe globe in regard to widespread transport ofash, its presence is nearly ubiquitous. However,the presence/absence of very fine-grained ash
material, and identification of its composition inparticular, is challenging given its broad classification as an “aluminosilicate” component insediment. Given this challenge, many studies
of ash have focused on discrete layers (that is,layers of ash that are of millimeter-to-centimeteror greater thickness, and their respective glass
shards) found in sequences at a variety of locations and timescales and how to link their presence with a number of Earth processes. The
ash that has been mixed into the bulk sediment,
known as dispersed ash, has been relatively
unstudied, yet represents a large fraction of
the total ash in a given sequence. The application of a combined geochemical and statistical technique has allowed identification of thisdispersed ash as part of the original ash contribution to the sediment. In this paper, we summarize the development of these geochemical/
statistical techniques and provide case studies
from the quantification of dispersed ash in the
Caribbean Sea, equatorial Pacific Ocean, andTop: Global distribution of subaerial volcanoes in different tectonic settings. Map has been modified after http://d-maps.com and volcano positions are taken from the Smithsonian Global Volcanism Program (http://

northwest Pacific Ocean. These geochemicalwww.volcano.si.edu).

studies (and their sedimentological precursors

Bottom: Locations of sites highlighted in this paper. Data from GeoMa-of smear slides) collectively demonstrate that

pApp (http://www.geomapapp.org; GMRT-Global Multi-Resolution Topog-

local and regional arc-related ash can be an

raphy; Ryan et al., 2009)

important component of sedimentary sequences
throughout large regions of the ocean.

Published: 2016/1/4
https://doi.org/10.1186/s40645-015-0077-y― 111 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Sea surface temperature proxies (alkenones, foraminiferal Mg/Ca, and planktonic foraminiferal
assemblage) and their implications in the Okinawa TroughKim R A, Lee K E, Bae S W[Keywords] Sea surface temperature, Okinawa Trough, Alkenone, Planktonic foraminiferal Mg/Ca ratio, Planktonic
foraminiferal assemblages

We reviewed three sea surface temperature(SST) proxies in the Okinawa Trough (OT):
alkenones, planktonic foraminiferal Mg/Ca, andplanktonic foraminiferal assemblages. The seasonal and vertical distribution patterns of eachproxy-related organism in the water column
were reviewed to confirm the applicability ofeach proxy. In addition, current SSTs (Japan
Oceanographic Data Center dataset from 1906
to 2003) were compared with core-top sedimenttemperatures reconstructed using the proxies.

Schematic diagram of SST proxy data in the OT. SST proxy data are given
for periods during the late Holocene (0–3 cal kyr BP) and LGM (18–21 cal
kyr BP). T indicates temperature.

Temperatures calculated using the alkenone
unsaturation index represent annual mean SSTs, and temperatures calculated using Mg/Ca of Globigerinoides ruber
capture summer to autumn (June–November) SSTs. Core-top August SSTs calculated from planktonic foraminiferal
assemblages corresponded well with the observed SSTs, but core-top February temperatures were ~3.6 °C warmer
than the observed SSTs. SST proxy estimates from marine sediments dating back to the late Holocene (0–3 cal ky BP)
and the last glacial maximum (18–21 cal ky BP) were compared. Comparisons between proxy SST estimates showthat foraminiferal assemblage-based August SSTs were the warmest. Alkenone-based temperature estimates werelower than Mg/Ca-based temperature estimates, probably because the alkenone-based temperature represents theannual mean temperature, whereas the Mg/Ca-based temperature represents the summer–autumn mean temperature.
February assemblage SSTs seem to be greatly affected by the statistical technique and/or database used. These
results suggest that seasonality should be considered in past SST reconstruction using alkenone and Mg/Ca in the
OT. The planktonic foraminiferal assemblage technique does not appear to be promising with respect to accurately
reconstructing past SSTs (especially winter) in the OT. Habitat depth may not be an issue because both alkenone
producers and G. ruber live at the upper surface mixed layer in the area.
Glacial–interglacial changes in the surface hydrography of the OT reconstructed based on the SST and salinity
proxies were also reviewed here. The surface hydrography of the OT has been influenced by changes in the Kuroshio
Current and the East Asian monsoon system during the late Quaternary. Comparisons of the hydrography records
from the OT with records of stalagmites in China, the Tropical Pacific, and the North Atlantic show that there is ateleconnection between them.

Published: 2015/12/1
https://doi.org/10.1186/s40645-015-0074-1― 112 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Marine tephra in the Japan Sea sediments as a tool for paleoceanography and paleoclimatology
Ikehara K[Keywords] Tephra, Key bed, Japan Sea, Stratigraphy, Chronology, Paleoceanography

Tephra is a product of large and explosive volcanic events and can travel thousands of kilometers before deposition. Consequently, tephra
deposits are common in terrestrial, lacustrine,
marine, and glacial environments. Because
tephra deposition is a geologically synchronous
event, tephras constitute important isochronesin the Quaternary sequence, not only in Japanbut also throughout the northwest Pacific andits marginal seas. As a result, establishing thechronostratigraphic order of tephra deposits isan effective tool for assessing local and regional
stratigraphies and for correlating events amongsites. For example, tephrostratigraphy can provide precise chronological constraints for otherDark-layer stratigraphy and tephra occurrences in the late Quaternarystratigraphic data, such as magneto- and bio-

Japan Sea sediments (A) and tephra occurrences in marine sedimentstratigraphic data. Spatiotemporal variability incores during MIS 3−5.3 (B)the occurrence and geochemistry of tephras
can also be used to trace the magmatic evolution of island arcs and their relationships to regional tectonics. In a
paleoclimatic context, tephra deposits allow the correlation of past climate events among terrestrial, lacustrine, andmarine environments. Tephrochronology is also a fundamental element used in reconstructing the marine reservoir
effect, where the ages of tephra in marine and terrestrial settings are compared. Therefore, tephra is a valuable tool
not only in stratigraphy, chronology, and volcanology but also in paleoceanography and paleoclimatology.

Published: 2015/11/16
https://doi.org/10.1186/s40645-015-0068-z― 113 ―

Progress in Earth and Planetary Science
https://progearthplanetsci.org/index.html

Review

Interdisciplinary research

The Pliocene to Recent History of the Kuroshio and Tsushima Currents: a multi-proxy approach
Gallagher S J, Kitamura A, Iryu Y, Itaki T, Koizumi I, Hoiles P[Keywords] Kuroshio Current, Tsushima Current, Pliocene, Pleistocene, Holocene, Paleoceanographic proxies,
Biogeography, Microfossils, Macrofossils, Geochemistry

The Kuroshio Current is a major western boundary current controlled by the North Pacific Gyre. It brings warm subtropical waters from the Indo-Pacific Warm Pool to Japan
exerting a major control on Asian climate. The Tsushima
Current is a Kuroshio offshoot transporting warm water
into the Japan Sea. Various proxies are used to determine the paleohistory of these currents. Sedimentologicalproxies such as reefs, bedforms, sediment source andsorting reveal paleocurrent strength and latitude. Proxies
such as coral and mollusc assemblages reveal past shelfal current activity. Microfossil assemblages and organic/
inorganic geochemical analyses determine paleo- sea surface temperature and salinity histories. Transportation oftropical palynomorphs and migrations of Indo-Pacific spe-

Figure 1: The southern path of the Kuroshio Current showing
the inferred extent of the Ryukyu Reefs in glacial and interglacial periods (adapted from Iryu et al. [2006])

cies to Japanese waters also reveal paleocurrent activity.
The stratigraphic distribution of these proxies suggests theKuroshio Current reached its present latitude (35 °N) by~3 Ma when temperatures were 1 to 2 °C lower than present. At this time a weak Tsushima Current broke throughTsushima Strait entering the Japan Sea. Similar oceanic
conditions persisted until ~2 Ma when crustal stretching
deepened the Tsushima Strait allowing inflow during every
interglacial. The onset of stronger interglacial/glacial cycles~1 Ma was associated with increased North Pacific Gyreand Kuroshio Current intensity. This triggered Ryukyu
Reef expansion when reefs reached their present latitude(~31 °N), thereafter the reef front advanced (~31 °N) andretreated (~25 °N) with each cycle. Foraminiferal proxy
data suggests eastward deflection of the Kuroshio Current
from its present path at 24 °N into the Pacific Ocean due
to East Taiwan Channel restriction during the Last Glacial
Maximum. Subsequently Kuroshio flow resumed its present trajectory during the Holocene. Ocean modeling andgeochemical proxies show that the Kuroshio Current path
may have been similar during glacials and interglacials,
however the glacial mode of this current remains controversial. Paleohistorical studies form important analogues
for current behavior with future climate change, however,there are insufficient studies at present in the region that
may be used for this purpose. Modeling of the response of

Figure 2: (i) The distribution of G. ruber and Tsushima Current molluscs in interglacials of the Omma Formation (adaptedfrom Kitamura and Kimoto [2006]) correlated to the LR04 benthic stack of Lisiecki and Raymo ([2005]). The red dots (1.6
to 1 Ma) are interglacials where migratory Indo-Pacific Warm
Pool benthic foraminifera are present (Hoiles et al. [2012]). Red
dots at 0 and ~3 Ma are Warm Pool benthic foram ingressions
described in Gallagher et al. ([2009]). Reconstructions of thepaleogeography of the Tsushima Strait after 1.6 Ma (ii) andprior to 1.7 Ma (iii) adapted from Kitamura and Kimoto ([2006])

the Kuroshio Current to future global warming reveals thatcurrent velocity may increase by up to 0.3 m/sec associated with a northward migration of the Kuroshio Extension.

Published: 2015/6/27
https://doi.org/10.1186/s40645-015-0045-6― 114 ―

The
The collection
collection ofof review
review articles
articlesProgress
in Earthand Planetary
Science(the 3rd edition: published from April 2014 to February 2023)

Japan Geoscience Union（JpGU）Open Access journal

https://progearthplanetsci.springeropen.com/

CONTENTS
1. Space and planetary sciences
Enstatite Chondrites: Condensation and Metamorphism under Extremely Reducing Conditions andContributions to the Earth ....................................................................................................................................  2
Natural and experimental high-pressure, shock-produced terrestrial and extraterrestrial materials ..................  3
Earth-affecting solar transients: a review of progresses in solar cycle 24 .........................................................   4
Role Of the Sun and the Middle atmosphere / thermosphere / ionosphere In Climate (ROSMIC):
a retrospective and prospective view ..................................................................................................................  5
Solar evolution and extrema: current state of understanding of long-term solar variability and its planetaryimpacts .................................................................................................................................................................  6
Terrestrial planet compositions controlled by accretion disk magnetic field .......................................................  7
Dynamics of the terrestrial radiation belts: A review of recent results during VarSITI (Variability of the Sun
and Its Terrestrial Impact) era, 2014-2018 ..........................................................................................................   8
A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial
Impact ..................................................................................................................................................................  9
Review of the accomplishments of Mid-latitude Super Dual Auroral Radar Network (SuperDARN)HF Radars ............................................................................................................................................................ 10
Scientific innovations from the Mars aerosol optical depth based on satellite data with a temporal
resolution of hours ............................................................................................................................................... 11
Simulation study of near-Earth space disturbances: 1. Magnetic storms ........................................................... 12
Simulation study of near-Earth space disturbances: 2. Auroral substorms ........................................................ 13
Day-to-day and short-term variabilities in the equatorial plasma bubble/spread F irregularity seeding anddevelopment ........................................................................................................................................................ 14
Asteroid Ryugu before the Hayabusa2 encounter .............................................................................................. 15
Review of the generation mechanisms of post-midnight irregularities in the equatorial and low-latitude
ionosphere ........................................................................................................................................................... 16
Lightning detection on Venus: a critical review ................................................................................................... 17
Post-sunset rise of equatorial F layer—or upwelling growth? ............................................................................ 18
Effects of the postsunset vertical plasma drift on the generation of equatorial spread F .................................. 19
A review on the numerical simulation of equatorial plasma bubbles toward scintillation evaluation andforecasting ........................................................................................................................................................... 20
Mars core structure — concise review and anticipated insights from InSight .................................................... 21
Extreme geomagnetically induced currents ........................................................................................................ 22
Magnetohydrodynamics Modeling of Coronal Magnetic Field and Solar Eruptions Based on the
Photospheric Magnetic Field ............................................................................................................................... 23
MF and HF radar techniques for investigating the dynamics and structure of the 50 to 110 km heightregion: a review ................................................................................................................................................... 24
Advancing the understanding of the Sun-Earth interaction - the Climate and Weather of the Sun-Earth
System (CAWSES) II Program ............................................................................................................................ 25
The science case for the EISCAT_3D radar ....................................................................................................... 26
Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II
period ................................................................................................................................................................... 27
eScience and Informatics for International Science Programs ........................................................................... 28
What is the solar influence on climate? Overview of activities during CAWSES-II ............................................ 29―i―Response of the mesosphere-thermosphere-ionosphere system to global change– CAWSES-II contribution ................................................................................................................................... 30
The geospace response to variable inputs from the lower atmosphere: A review of the progress made by
Task Group 4 of CAWSES-II ............................................................................................................................... 31

2. Atmospheric and hydrospheric sciences
The response of the hydrological cycle to temperature changes in recent and distant climatic history ............ 34
Marine microplastics as vectors of major ocean pollutants and its hazards to the marine ecosystem andhumans ................................................................................................................................................................ 35
Applications of soft computing models for predicting sea surface temperature: a comprehensive review
and assessment ................................................................................................................................................... 36
Two decades of Earth system modeling with an emphasis on Model for Interdisciplinary Research on
Climate (MIROC) ................................................................................................................................................. 37
d4PDF: large-ensemble and high-resolution climate simulations for global warming risk assessment ............. 38
DYAMOND: The DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains .... 39
Toward reduction of the uncertainties in climate sensitivity due to cloud processes using a global
non-hydrostatic atmospheric model ..................................................................................................................... 40
Maritime continent coastlines controlling Earth’s climate .................................................................................... 41
Outcomes and challenges of global high-resolution non-hydrostatic atmospheric simulations using
the K computer .................................................................................................................................................... 42
A review of atmospheric chemistry observation at mountain sites ..................................................................... 43
A review of progress towards understanding the transient global mean surface temperature response toradiative perturbation ........................................................................................................................................... 44
Overview of the development of the Aerosol Loading Interface for Cloud microphysics
In Simulation (ALICIS) ......................................................................................................................................... 45
The dynamics of the mesosphere and lower thermosphere: a brief review ....................................................... 46
Modeling in Earth system science up to and beyond IPCC AR5 ....................................................................... 47
The Non-hydrostatic Icosahedral Atmospheric Model: Description and Development ....................................... 48

3. Human geosciences・Biogeosciences
Geomorphological processes and their connectivity in hillslope, fluvial, and coastal areas in Bangladesh:
A review ............................................................................................................................................................... 50
A review of theoretical salt weathering studies for stone heritage ..................................................................... 51
Arsenic cycling in the Earth’s crust and hydrosphere: interaction between naturally occurring arsenic andhuman activities ................................................................................................................................................... 52
Liquid and supercritical CO2 as an organic solvent in Hadean seafloor hydrothermal systems:
implications for prebiotic chemical evolution ....................................................................................................... 53
Perspective on the response of marine calcifiers to global warming and ocean acidification– Behavior of corals and foraminifera in a high CO2 world “hot house” ............................................................. 54
Theoretical constraints of physical and chemical properties of hydrothermal fluids on variations inchemolithotrophic microbial communities in seafloor hydrothermal systems. .................................................... 55
Biochemical and physiological bases for the use of carbon and nitrogen isotopes in environmental andecological studies ................................................................................................................................................ 56

4. Solid earth sciences
Significance of the high-pressure properties and structural evolution of gas hydrates for inferring
the interior of icy bodies ...................................................................................................................................... 58― ii ―

A review on slow earthquakes in the Japan Trench ........................................................................................... 59
The role of hydrogen bonds in hydrous minerals stable at lower mantle pressure conditions .......................... 60
Fluids and physicochemical properties and processes in the Earth ................................................................... 61
DigitSeis: Software to Extract Time Series from Analogue Seismograms .......................................................... 62
Review of the Early–Middle Pleistocene boundary and Marine Isotope Stage 19 ............................................. 63
Visualizing heterogeneities of earthquake hypocenter catalogs: modeling, analysis, and compensation ......... 64
Strength models of the terrestrial planets and implications for their lithospheric structure and evolution ......... 65
Deep mantle melting, global water circulation and its implications for the stability of the ocean mass ............ 66
A coupled core-mantle evolution: Review and future prospects ......................................................................... 67
Some remarks on hydrogen-assisted electrical conductivity in olivine and other minerals ............................... 68
Detection of repeating earthquakes and their application in characterizing slow fault slip ................................ 69
Nitrogen in the Earth: abundance and transport ................................................................................................. 70
Earthquake Early Warning: what does “seconds before a strong hit” mean? .................................................... 71
Redox-controlled mechanisms of C and H isotope fractionation between silicate melt and COH fluidin the Earth’s interior ............................................................................................................................................ 72
Nonlinear dynamical analysis of GNSS data: quantification, precursors and synchronization .......................... 73
Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California:
insight into mélange origins and subduction-accretion processes ...................................................................... 74
Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes .................. 75
Imaging in 3D under pressure: a decade of high-pressure X-ray microtomography development at
GSECARS ............................................................................................................................................................ 76
Philippine Sea Plate inception, evolution and consumption with special emphasis on the early stages of
Izu-Bonin-Mariana subduction ............................................................................................................................. 77
Mantle hydration and Cl-rich fluids in the subduction forearc ............................................................................. 78
Iron snow, crystal floats, and inner-core growth: modes of core solidification and implications for
dynamos in terrestrial planets and moons .......................................................................................................... 79
Liquid Sodium Models of the Earth’s Core .......................................................................................................... 80
Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary
dynamos .............................................................................................................................................................. 81
Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison withseismic models .................................................................................................................................................... 82
Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms ............................... 83
Water-melt interaction in hydrous magmatic systems at high temperature and pressure ................................. 84

5. Interdisciplinary research
Identifying key processes and sectors in the interaction between climate and socio-economic systems:
a review toward integrating Earth–human systems ............................................................................................ 86
Coupling library Jcup3: its philosophy and application ....................................................................................... 87
Morphometric measurements of bedrock rivers at different spatial scales and applications togeomorphological heritage research ................................................................................................................... 88
Northern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change
in the twenty-first century .................................................................................................................................... 89
Cenozoic sedimentary records of climate-tectonic coupling in the Western Himalaya ...................................... 90― iii ―

Transitional changes in microfossil assemblages in the Japan Sea from the Late Pliocene to
Early Pleistocene related to global climatic and local tectonic events ............................................................... 91
Evolution and variability of the Asian monsoon and its potential linkage with uplift of the Himalaya andTibetan Plateau .................................................................................................................................................... 92
Geochemical approaches to the quantification of dispersed volcanic ash in marine sediment ......................... 93
Sea surface temperature proxies (alkenones, foraminiferal Mg/Ca, and planktonic foraminiferal assemblage)
and their implications in the Okinawa Trough ..................................................................................................... 94
Marine tephra in the Japan Sea sediments as a tool for paleoceanography and paleoclimatology .................. 95
The Pliocene to Recent History of the Kuroshio and Tsushima Currents: a multi-proxy approach ................... 96― iv ―

Review
Space and planetary sciences

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Enstatite Chondrites: Condensation and Metamorphism under Extremely Reducing Conditions
and Contributions to the Earth
Yangting Lin[Keywords] enstatite chondrite, condensation of the solar nebula, reducing conditions, inner solar system, building
blocks of the EarthEnstatite chondrites are a small clan of meteorites,
only ~ 1% out of all meteorite collection. However, they
are the most reduced meteorites and have almost identicalisotopic compositions to those of the Earth, suggestive ofsignificant contributions to the latter and other terrestrial
planets. Enstatite chondrites contain a unique mineralinventory of sulfides of typical lithophile elements,
Si-bearing metal, silicide and phosphide, which record
the nebular processes and the thermal metamorphism inasteroidal bodies under extremely reducing environments.
EH group is mainly characteristic of the higher Si content
of metallic Fe–Ni and the higher MnS contents of sulfides
than EL group, indicative of a more reducing condition thanthe latter. However, the fugacity pH2S could be the same
in both EH and EL regions, because it was buffered by

The compositions of (Mg,Mn,Fe)S, a key indicator for condensation and metamorphism of enstatite chondrites

kamacite and troilite. The majority of sulfides condensed
from the nebula, partially enclosing schreibersite micron-spherules formed probably by early melting. Another part oftroilite, sphalerite and djerfisherite, intergrown with perryite, were produced via sulfidation of metallic Fe–Ni. Minor
exotic components were also found in enstatite chondrites, including Ca-, Al-rich inclusions and FeO-rich silicate clasts.
The Ca-, Al-rich inclusions are identical to those in carbonaceous chondrites except for the alteration under reducing
environments, and the FeO-rich silicate clasts show reduction reactions, both suggestive of migration of dust in the
protoplanetary disk. The highly reducing conditions (as C/O ratios) might be established via repeating evaporationand condensation of water ice and organic matter across the snow line along the protoplanetary disk, but need tofind evidence. Another issue is the preservation of submicron-to-micron-sized presolar grains during high-temperaturecondensation of the major constituent minerals. After accretion, the parent bodies of EH and EL chondrites probably
experienced distinct thermal histories, indicated by their distinct petrologic-type distributions and different correlations
with the closure temperatures determined by the FeS contents of sulfides in contact with troilite.
The composition of (Mg, Mn, Fe)S, a key indicator for condensation and metamorphism of enstatite chondrites.

Published: 2022/5/20
https://doi.org/10.1186/s40645-022-00483-6―2―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Natural and experimental high-pressure, shock-produced terrestrial and extraterrestrial materials
Masaaki Miyahara, Naotaka Tomioka, Luca Bindi[Keywords] High-pressure mineral, Shock metamorphism, Meteorite, Impact crater

Hypervelocity impacts are among the fundamental
phenomena occurring during the evolution of the solar
system and are characterized by instantaneous ultrahighpressure and temperature. Varied physicochemicalchanges have occurred in the building blocks of celestialbodies under such extreme conditions. The constituent
material has transformed into a denser form, a highpressure polymorph. The high-pressure polymorph isalso thought to be the constituent of the deep Earth’s
interior. Hence, experiments using a high-pressure andtemperature generating apparatus have been conducted
to clarify its crystal structure, pressure-temperaturestability range, and transformation mechanisms. A natural
high-pressure polymorph (mineral) is found from terrestrial
and extraterrestrial rocks that experienced a hypervelocity
impact. Mineralogists and planetary scientists have

A meteorite with shock-induced melting and high-pressuremineral.

investigated high-pressure minerals in meteorites androcks near terrestrial craters over a half-century. Here,
we report brief reviews about the experiments producing
high-pressure polymorphs and then summarize theresearch histories of high-pressure minerals occurringin shocked meteorites and rocks near terrestrial craters.
Finally, some implications of high-pressure minerals foundin impact-induced shocked rocks are also mentioned.

Published: 2021/10/18
https://doi.org/10.1186/s40645-021-00451-6―3―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Earth-affecting Solar Transients: A Review of Progresses in Solar Cycle 24
Jie Zhang, Manuela Temmer, Nat Gopalswamy, Olga Malandraki, Nariaki V. Nitta, Spiros Patsourakos, Fang
Shen, Bojan Vrsnak, Yuming Wang, David Webb, Mihir Desa, Karin Dissauer, Nina Dresing, Mateja Dumbovic,
Xueshang Feng, Stephan Heinemann, Monica Laurenza, Noe Lugaz, Bin Zhuang[Keywords] Coronal Mass Ejection, Interplanetary Coronal Mass Ejection, Solar Energetic Particle, Corotating
Interaction Region, Flare, Corona, Sun, Geomagnetic Storms, Space Weather

This review article summarizes theadvancement in the studies of Earth-affecting solar transients in the last decade thatencompasses most of solar cycle 24. It is apart of the effort of the International Studyof Earth-affecting Solar Transients (ISEST)
project, sponsored by the SCOSTEP/VarSITI program (2014-2018). The Sun-Earthis an integrated physical system in which
the space environment of the Earth sustains
continuous influence from mass, magnetic
field, and radiation energy output of the Sunin varying timescales from minutes to millennium. This article addresses short timescale
events, from minutes to days that directly
cause transient disturbances in the Earth’s
space environment and generate intense

A schematic of CMEs (lower, center) from the Sun to the Earth. Their man-adverse effects on advanced technologicalifestations near the Sun (upper left) and at 1 AU (upper right) both contain asystems of human society. Such transient

shock-sheath component (red) and flux rope component (blue)

events largely fall into the following fourtypes: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar
energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions(CIRs). In the last decade, the unprecedented multi-viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided
much more accurate and global measurements of the size, speed, propagation direction, and morphology of CMEs inboth 3D and over a large volume in the heliosphere. Many CMEs, fast ones, in particular, can be clearly characterized
as a two-front (shock front plus ejecta front) and three-part (bright ejecta front, dark cavity, and bright core) structure.
Drag-based kinematic models of CMEs are developed to interpret CME propagation in the heliosphere and are applied
to predict their arrival times at 1 AU in an efficient manner. Several advanced MHD models have been developed
to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been
made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformationof CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also
been significantly improved. An outlook of how to address critical issues related to Earth-affecting solar transientsconcludes this article.

Published: 2021/10/5
https://doi.org/10.1186/s40645-021-00426-7―4―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Role Of the Sun and the Middle atmosphere / thermosphere / ionosphere In Climate (ROSMIC):
a retrospective and prospective view
Ward W, Seppälä A, Yiğit E, Nakamura T, Stolle C, Laštovička J, Woods TN, Tomikawa Y, Lübken FJ, Solomon
SC, Marsh DR, Funke B, Pallamraju D[Keywords] Climate, Atmosphere, Middle atmosphere, Thermosphere, Ionosphere, Solar irradiance, Energetic
particles, Atmospheric coupling, Trends

While knowledge of the energy inputs fromthe Sun (as it is the primary energy source) is
important for understanding the solar-terrestrial system, of equal importance is the manner in which the terrestrial part of the systemorganizes itself in a quasi-equilibrium state toaccommodate and re-emit this energy. The
ROSMIC project (2014-2018 inclusive) was
the component of SCOSTEP’s Variability of the
Sun and Its Terrestrial Impact (VarSITI) program
which supported research into the terrestrial
component of this system. The four themes

Links in the middle atmosphere. A schematic showing the relationshipsupported under ROSMIC are solar influence

between various components affecting the large-scale structure of theon climate, coupling by dynamics, trends in the

middle atmosphere. The main elements appear in the green boxes, andmesosphere lower thermosphere, and trends

the processes linking them appear in the blue boxes. The arrows indicate

and solar influence in the thermosphere. Overthe direction of the influence.

the course of the VarSITI program, scientificadvances were made in all four themes. This included improvements in understanding (1) the transport of photochemically produced species from the thermosphere into the lower atmosphere; (2) the manner in which waves produced in
the lower atmosphere propagate upward and influence the winds, dynamical variability, and transport of constituentsin the mesosphere, ionosphere, and thermosphere; (3) the character of the long-term trends in the mesosphere andlower thermosphere; and (4) the trends and structural changes taking place in the thermosphere. This paper reviews
the progress made in these four areas over the past 5 years and summarizes the anticipated research directions inthese areas in the future. It also provides a physical context of the elements which maintain the structure of the terrestrial component of this system. The effects that changes to the atmosphere (such as those currently occurring asa result of anthropogenic influences) as well as plausible variations in solar activity may have on the solar terrestrial
system need to be understood to support and guide future human activities on Earth.

Published: 2021/8/18
https://doi.org/10.1186/s40645-021-00433-8―5―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Solar evolution and extrema: current state of understanding of long-term solar variability and its
planetary impacts
Nandy D., Martens P.C.H., Obridko V., Dash S., Georgieva K.
[Keywords] Solar magnetic fields, Stellar evolution, Stellar flares, Stellar wind, Space weather, Space climate, Faint
Young Sun paradox, Star planet interactions, Planetary evolution, Habitability

The activity of stars such as the Sun varies overtimescales ranging from the very short to the very longstellar and planetary evolutionary timescales. Experiencefrom our solar system indicates that short-term, transient
events such as stellar flares and coronal mass ejections
create hazardous space environmental conditions that
impact Earth-orbiting satellites and planetary atmospheres.
Extreme events such as stellar superflares may play a role inatmospheric mass loss and create conditions unsuitable forlife. Slower, long-term evolutions of the activity of Sun-like

Stellar wind–planet interactions

stars over millennia to billions of years result in variations
in stellar wind properties, radiation flux, cosmic ray flux, and frequency of magnetic storms. This coupled evolution ofstar-planet systems eventually determines planetary and exoplanetary habitability. The Solar Evolution and Extrema(SEE) initiative of the Variability of the Sun and Its Terrestrial Impact (VarSITI) program of the Scientific Committee
on Solar-Terrestrial Physics (SCOSTEP) aimed to facilitate and build capacity in this interdisciplinary subject of broadinterest in astronomy and astrophysics. In this review, we highlight progress in the major themes that were the focusof this interdisciplinary program, namely, reconstructing and understanding past solar activity including grand minima
and maxima, facilitating physical dynamo-model-based predictions of future solar activity, understanding the evolutionof solar activity over Earth’s history including the faint young Sun paradox, and exploring solar-stellar connections withthe goal of illuminating the extreme range of activity that our parent star-the Sun-may have displayed in the past, or
may be capable of unleashing in the future.

Published: 2021/7/5
https://doi.org/10.1186/s40645-021-00430-x―6―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Terrestrial planet compositions controlled by accretion disk magnetic field
William F McDonough, Takashi Yoshizaki[Keywords] planetary formation, planetary composition, accretionary disk, magnetic field

Terrestrial planets (Mercury, Venus, Earth,and Mars) are differentiated into three layers:a metallic core, a silicate shell (mantle andcrust), and a volatile envelope of gases, ices,and, for the Earth, liquid water. Each layer has
different dominant elements (e.g., increasingiron content with depth and increasing oxygen
content to the surface). Chondrites, the building
blocks of the terrestrial planets, have mass andatomic proportions of oxygen, iron, magnesium,and silicon totaling ≥ 90% and variable Mg/Si(∼ 25%), Fe/Si (factor of ≥2), and Fe/O (factorof ≥ 3). What remains an unknown is to what
degree did physical processes during nebular

Density of the rocky solar system bodies. Uncompressed and solid den-disk accretion versus those during post-nebular

sities are shown for terrestrial planets and chondrites (grey), respectively.

disk accretion (e.g., impact erosion) influence

Bulk planetary densities are shown for asteroids (blue).

these planets final bulk compositions. Here we
predict terrestrial planet compositions and show that their core mass fractions and uncompressed densities correlatewith their heliocentric distance, and follow a simple model of the magnetic field strength in the protoplanetary disk. Ourmodel assesses the distribution of iron in terms of increasing oxidation state, aerodynamics, and a decreasing magnetic
field strength outward from the Sun, leading to decreasing core size of the terrestrial planets with radial distance. This
distribution enhances habitability in our solar system and may be equally applicable to exoplanetary systems.

Published: 2021/7/2
https://doi.org/10.1186/s40645-021-00429-4―7―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Dynamics of the terrestrial radiation belts: A review of recent results during VarSITI (Variabilityof the Sun and Its Terrestrial Impact) era, 2014-2018
Kanekal S., Miyoshi Y.
[Keywords] Inner Magnetosphere, Energetic Particles, Plasma Waves, Wave-Particle Interactions, Radiation Belts,
Plasmasphere, Ring Current

The Earth’s magnetosphere is region thatis carved out by the solar wind as it flows pastand interacts with the terrestrial magnetic
field. The inner magnetosphere is the region
that contains the plasmasphere, ring current,
and the radiation belts all co-located within
about 6.6 Re, nominally taken to be bounding
this region. This region is highly dynamic andis home to a variety of plasma waves andparticle populations ranging in energy from a
few eV to relativistic and ultra-relativistic electrons and ions. The interplanetary magnetic
field (IMF) embedded in the solar wind via
the process of magnetic reconnection at the
sub-solar point sets up plasma convection
and creates the magnetotail. Magnetic recon-

Diagram illustrating the interconnectedness and cross-energy coupling
between particles, waves, and underlying physical processes.

nection also occurs in the tail and is responsible for explosive phenomena known as substorms. Substorms inject low-energy particles into the inner magnetosphereand help generate and sustain plasma waves. Transients in the solar wind such as coronal mass ejections (CMEs),
co-rotating interaction regions (CIRs), and interplanetary shocks compress the magnetosphere resulting in geomagnetic storms, energization, and loss of energetic electrons in the outer radiation belt nad enhance the ring current,
thereby driving the geomagnetic dynamics. The Specification and Prediction of the Coupled Inner-Magnetospheric
Environment (SPeCIMEN) is one of the four elements of VarSITI (Variability of the Sun and Its Terrestrial Impact)
program which seeks to quantitatively predict and specify the inner magnetospheric environment based on Sun/solar
wind driving inputs. During the past 4 years, the SPeCIMEN project has brought together scientists and researchers
from across the world and facilitated their efforts to achieve the project goal. This review provides an overview ofsome of the significant scientific advances in understanding the dynamical processes and their interconnectedness
during the VarSITI era. Major space missions, with instrument suites providing in situ measurements, ground-based
programs, progress in theory, and modeling are briefly discussed. Open outstanding questions and future directionsof inner magnetospheric research are explored.

Published: 2021/5/31
https://doi.org/10.1186/s40645-021-00413-y―8―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

A review of the SCOSTEP’s 5-year scientific program VarSITI—Variability of the Sun and Its Terrestrial Impact
Shiokawa K, Georgieva K[Keywords] VarSITI, Variability of the Sun and its terrestrial impact, Sun, Heliosphere, Inner magnetosphere.
Ionosphere, Thermosphere, Middle atmosphere, Climate change, Space weather

The Sun is a variable active-dynamo star, emitting radiation in all wavelengths and solar-wind plasma to the interplanetary space. The Earth is immersed in this radiation and solar wind, showing various responses in geospace andatmosphere. This Sun-Earth connection variates in time scales from milli-seconds to millennia and beyond. The solar
activity, which has a ~11-year periodicity, is gradually declining in recent three solar cycles, suggesting a possibilityof a grand minimum in near future. VarSITI-variability of the Sun and its terrestrial impact-was the 5-year programof the scientific committee on solar-terrestrial physics (SCOSTEP) in 2014-2018, focusing on this variability of the
Sun and its consequences on the Earth. This paper reviews some background of SCOSTEP and its past programs,
achievements of the 5-year VarSITI program, and remaining outstanding questions after VarSITI.

Fig1: Logo of the VarSITI program

Fig2: Black: challenging scientific topics in the solar-terrestrial coupling
during and after the VarSITI program. Red: their consequences on human
life. Short and long-term variabilities are shown in the left and right sideof the figure, respectively. CIR corotating interaction region, CME coronalmass ejection, CR cosmic ray, IMF interplanetary magnetic field, GNSS
global navigation satellite system, GW gravity wave, MHD magnetohydrodynamics, PW planetary wave, UV ultraviolet

Published: 2021/3/9
https://doi.org/10.1186/s40645-021-00410-1―9―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Review of the accomplishments of Mid-latitude Super Dual Auroral Radar Network (SuperDARN)HF Radars
Nishitani N, Ruohoniemi JM, Lester M, Baker JBH, Koustov AV, Shepherd SG, Chisham G, Hori T, ThomasEG, Makarevich RA, Marchaudon A, Ponomarenko P, Wild JA, Milan SE, Bristow WA, Devlin J, Miller E,
Greenwald RA, Ogawa T, Kikuchi T[Keywords] Mid-latitude SuperDARN, Ionosphere, Magnetosphere, Convection, Ionospheric irregularities, HF
propagation analysis, Ion-neutral interactions, MHD waves

The Super Dual Auroral Radar Network(SuperDARN) is a network of high-frequency(HF) radars located in the high- and mid-latitude regions of both hemispheres that is
operated under international cooperation. The
network was originally designed for monitoring the dynamics of the ionosphere and upper
atmosphere in the high-latitude regions. However, over the last approximately 15 years,
SuperDARN has expanded into the mid-latitude

Schematic plots showing the a Northern and b Southern Hemisphere

regions. With radar coverage that now extends

SuperDARN radar locations with respect to the auroral oval. The model

continuously from auroral to sub-auroral andauroral oval (yellow) for moderately disturbed conditions is plotted with

mid-latitudes, a wide variety of new scientific

the SuperDARN radar locations identified in green type and green closed

findings have been obtained. In this paper,

circles (polar cap latitudes), blue type and blue closed circles (auroral

the background of mid-latitude SuperDARN islatitudes), and black type and red closed circles (mid-latitude radars).

presented at first. Then, the accomplishments
made with mid-latitude SuperDARN radars
are reviewed in five specified scientific andtechnical areas: convection, ionospheric irregularities, HF propagation analysis, ion-neutralinteractions, and magnetohydrodynamic (MHD)
waves. Finally, the present status of mid-latitude
SuperDARN is updated and directions for future
research are discussed.

Schematic illustration of natural phenomena which can be studied bySuperDARN radars.

Published: 2019/3/18
https://doi.org/10.1186/s40645-019-0270-5― 10 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Scientific innovations from the Mars aerosol optical depth based on satellite data with a temporal resolution of hours
Gebhardt C, Abuelgasim A.
[Keywords] ExoMars Trace Gas Orbiter (TGO), Emirates Mars Mission (EMM), Mars stationary satellites, Mars
atmosphere, Aerosol optical depth, Dust, Water ice clouds, Mars climatology, Mars numerical weather forecasting,
Data assimilation

The ExoMars Trace Gas Orbiter (TGO), Emirates Mars Mission (EMM), and possible futureMars stationary satellite(s) will provide innovative data products on the optical depth of dust
and water ice clouds in the Martian atmospherewith a temporal resolution of hours. The science phase of TGO has begun in April 2018,
and the EMM science operation is scheduled
to start in 2021. In this work, the relationshipbetween TGO, EMM, and precursor missions/
instruments is analyzed based on the obtained
data products. This is followed by discussing
the foreseen innovation from the latter in the fields of Martian climatology and numerical weather forecasting.

Published: 2019/3/28
https://doi.org/10.1186/s40645-019-0276-z― 11 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Simulation study of near-Earth space disturbances: 1. Magnetic storms
Ebihara Y.
[Keywords] Magnetic storms, Computer simulation, Magnetosphere, Ionosphere, Inner magnetosphere, and Ring
current.

A magnetic storm is the world-wide geomagnetic disturbance taking place in near-Earthspace environment, lasting for a few days.
Geomagnetic fields can be depressed by ~1%on the ground for large magnetic storms. The
prime cause of the long-lasting, world-wide geomagnetic disturbance is the development of thering current that surrounds the Earth. The ring
current is an electric current carried by charged
particles. Thus, the growth and decay of the ring
current correspond to accumulation and loss of
the ring current particles, respectively. The ring
current is strong enough to modulate near-Earthspace environment, and leads to many observable effects. In this sense, the ring current can

Cross energy and cross region coupling in the inner magnetosphere andthe ionosphere.

be regarded as an important mediator in thenear-Earth space environment. Here, the dynamics and structure of the ring current and its active role are briefly
reviewed on the basis of numerical simulation results.

Published: 2019/2/13
https://doi.org/10.1186/s40645-019-0264-3― 12 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Simulation study of near-Earth space disturbances: 2. Auroral substorms
Yusuke Ebihara[Keywords] Substorm, Aurora, Computer simulation, Magnetosphere, and Ionosphere.

A substorm is a transient phenomenon thatlasts for only 1–2 h. One significant manifestation of the substorm is a sudden brightening of
the aurora on the nightside. Simultaneously, theauroral electrojets are abruptly intensified in theionosphere, disturbing the geomagnetic field in
the polar region. The near-Earth space environment is highly disturbed, which manifests as anearthward fast flow of plasma, a sudden change
in the magnetic field, or a sudden increase in
hot plasma. Such disturbances are known toseverely affect human society. The ultimate
cause of the disturbances is the solar wind,
but an explanation of the chain of processes
leading from solar wind to the ionosphere is
problematic. Here, the evolution of the auroral
substorm is reviewed based on the results ofa global magnetohydrodynamics (MHD) sim-

Conceptual illustration of possible chain reaction of an auroral substorm inulation, called a REProduce Plasma Universe

terms of energy transfer from the solar wind to the ionosphere.

(REPPU) code. The REPPU code is shown toreproduce many aspects of the auroral substorms and to be useful for understanding the primary chain processes
from the solar wind to the ionosphere.

Published: 2019/3/5
https://doi.org/10.1186/s40645-019-0273-2― 13 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Day-to-day and short-term variabilities in the equatorial plasma bubble/spread F irregularity
seeding and development
Mangalathayil Ali Abdu
[Keywords] Equatorial ionosphere, Plasma bubbles/spread F irregularities, Prereversal vertical drift, Prompt penetrationelectric field, Gravity waves, Trans-equatorial wind, Planetary/Kelvin waves, ESF/EPB short-term variability

The background ionospheric conditions
shaped by sunset electrodynamic processes
are responsible for the development of equatorial plasma bubble (EPB)/equatorial spread
F (ESF) irregularities of the post-sunset ionosphere. Distinct conditions exist for the EPB/
ESF development also at later hours of thenight. The plasma instability growth leading
to EPB generation is dependent on the basic
precursor conditions defined by the well-known
parameters: the evening prereversal enhancement in vertical plasma drift (PRE), wave structure in plasma density and polarization electricfield required to initiate/seed the instability, andthe F layer bottom side density gradient, as asignificant factor in controlling the growth rate. Competing roles of the zonal versus meridional thermospheric winds
additionally control their development. Statistical as well as case studies have addressed aspects of the EPB development and occurrence under different geophysical conditions, generally focusing attention on any one of the above
specific parameters. Little is known regarding the relative importance of concurrent presence of the precursor parameters (mentioned above) in shaping a given event. A large degree of day-to-day variability in these parameters arise
from different sources of forcing, such as upward propagating atmospheric waves, and magnetic disturbance timeelectric fields in the form of prompt penetration and disturbance dynamo electric fields that often contribute to thewidely observed short-term variabilities in EPB development and dynamics. In this paper, we will present and discuss
some important aspects of the EPB/ESF short-term variability, focusing attention on their enhanced development, or
suppression and, wherever possible, highlighting also the relative roles of the precursor parameters in such variability.

Published: 2019/2/1
https://doi.org/10.1186/s40645-019-0258-1― 14 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Asteroid Ryugu before the Hayabusa2 encounter
Wada K, Grott M, Michel P, Walsh K, Barucci A, Biele J, Blum J, Ernst C, Grundmann J, Gundlach B,
Hagermann A, Hamm M, Jutzi M, Kim M, Kührt E, Le Corre L, Libourel G, Lichtenheldt R, Maturilli A,
Messenger S, Michikami T, Miyamoto H, Mottola S, Müller T, Nakamura A, Nittler L, Ogawa K, Okada T,
Palomba E, Sakatani N, Schröder S, Senshu H, Takir D, Zolensky M and International Regolith Science
Group (IRSG) in Hayabusa2 project[Keywords] Hayabusa2, Ryugu, Asteroids, Regolith, Physical properties

Asteroid (162173) Ryugu is the target objectof Hayabusa2, an asteroid exploration andsample return mission led by Japan Aerospace
Exploration Agency (JAXA). Ground-based
observations indicate that Ryugu is a C-typenear-Earth asteroid with a diameter of lessthan 1 km, but the knowledge of its detailed
properties is very limited prior to Hayabusa2
observation. This paper summarizes our best
understanding of the physical and dynamical
properties of Ryugu based on ground-based
remote sensing and theoretical modeling before
the Hayabusa2’s arrival at the asteroid. This
information is used to construct a design reference model of the asteroid that is used forContour plot of thermal inertia (in units of J m−2 s−1/2 K−1) as a function of
typical particle diameter and porosity (see text for the regolith parametersassumed in the calculation). The gray-filled region indicates the thermal
inertia range estimated for Ryugu by ground-based observations (Müller

the formulation of mission operation plans in

et al. 2017). From this figure, we can estimate a typical particle size foradvance of asteroid arrival. Particular attention

the Ryugu regolith.

is given to the surface properties of Ryugu thatare relevant to sample acquisition. This reference model helps readers to appropriately interpret the data that will bedirectly obtained by Hayabusa2 and promotes scientific studies not only for Ryugu itself and other small bodies but
also for the solar system evolution that small bodies shed light on.

Published: 2018/12/11
https://doi.org/10.1186/s40645-018-0237-y― 15 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Review of the generation mechanisms of post-midnight irregularities in the equatorial andlow-latitude ionosphere
Otsuka Y[Keywords] Equatorial ionosphere, Ionospheric irregularity, Rayleigh–Taylor instability, Plasma bubble

This paper provides a brief review of ionospheric irregularities that occur in magneticallyequatorial and low-latitude regions post-midnight during low solar activity periods. Ionospheric irregularities can occur in equatorial
plasma bubbles. Plasma bubbles are wellknown to frequently occur post-sunset when thesolar terminator is nearly parallel to the geomagnetic field lines (during equinoxes at thelongitude where the declination of the geomagnetic field is almost equal to zero and near the
December solstice at the longitude where thedeclination is tilted westward), especially duringhigh solar activity conditions via the Rayleigh–Taylor instability. However, recent observations
during a solar minimum period show a highoccurrence rate of irregularities post-midnightaround the June solstice. The mechanisms forgenerating the post-midnight irregularities arestill unknown, but two candidates have been
proposed. One candidate is the seeding of theRayleigh–Taylor instability by atmospheric gravity waves propagating from below into the ionosphere. The other candidate is the uplift of theRange-time-intensity plot of the field-aligned irregularity (FAI) echo in the

F layer by the meridional neutral winds in the

F region observed on the five beams of a VHF radar in Indonesia on thethermosphere, which may be associated withnights of August 21, 2007. (after Otsuka et al. 2009)

midnight temperature maximums in the thermosphere.

Published: 2018/9/20
https://doi.org/10.1186/s40645-018-0212-7― 16 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Lightning detection on Venus: a critical review
Ralph D. Lorenz[Keywords] Venus, Lightning, Electromagnetic emission, Observation

Claimed detections and nondetections oflightning and related electromagnetic emissions
on Venus are qualitatively contradictory. Here,motivated by the commencement of observations by the Akatsuki spacecraft and by studies
of future missions, we critically review spacecraft and ground-based observations of thepast 40 years, in an attempt to reconcile thediscordant reports with a minimal number ofassumptions. These include invoking alternative interpretations of individual reports, guided
by sensitivity thresholds, controls, and otherobjective benchmarks of observation integrity.
The most compelling evidence is in fact the first,
the very low frequency (VLF) radio emissions
recorded beneath the clouds by all four of the
Veneras 11–13 landers, and those data are
re-examined closely, finding power-law amplitude characteristics and substantial differences
between the different profiles. It is concluded
that some kind of frequent electrical activity is supported by the preponderance of observations, but optical emissions
are not consistent with terrestrial levels of activity. Venus’ activity may, like Earth’s, have strong temporal and/or spatial
variability, which coupled with the relatively short accumulated observation time for optical measurements, can leadto qualitative discrepancies between observation reports. We note a number of previously unconsidered observations
and outline some considerations for future observations.

Published: 2018/6/2
https://doi.org/10.1186/s40645-018-0181-x― 17 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Post-sunset rise of equatorial F layer—or upwelling growth?
Tsunoda R T, Saito S, Nguyen T T[Keywords] Equatorial plasma bubbles, Equatorial spread F, Day-to-day variability, Post-sunset rise of equatorial F
layer, Large-scale wave structure, Upwelling paradigm, Upwelling growth, Pre-reversal enhancement, Electric field,
Equatorial ionosphere

According to the so-called upwelling paradigm, development of equatorial plasma bubbles (EPBs) involves (1) appearance of an
upwelling (i.e., local uplift with a zonal width of~400 km) in the bottomside of the equatorial F
layer, (2) its growth via the F-region interchange
instability during the post-sunset rise (PSSR) of
the F layer, and (3) launching of EPBs, whichstarts near the end of PSSR, from within theconfines of the upwelling. In this description, the
PSSR is presumed to be the primary driver ofthe paradigm, with upwelling growth dependent
on PSSR strength. As constructed, the paradigm describes EPB development when PSSR
is strong (i.e., high solar activity), but not when
it is weak. We, show, for the first time, that when
PSSR is weak (e.g., low solar activity), upwelling growth can still be comparable in strength
to what would be considered a strong PSSR,
and that this growth drives EPB development.
Given that EPBs do not develop outside of
upwellings, regardless of solar activity, we are
led to conclude, against mainstream thinking,that the controlling driver for EPB development
is upwelling growth, not PSSR. For continued
progress toward understanding EPB development, a crucial next step is to identify the source
mechanism for upwelling growth, especiallyCurves of h’F (2.5) vs UT, for two quiet nights (20 and 22 March 2006),
and one disturbed night (27 March 2006). The green (red) curve is for BCL(CPN). The gray curve is h’F (2.5) vs LST for CPN. Two levels for range
type of ESF are shown, weak and strong; they should be used with the
UT scale. Mean SSN for 2006 was 15.2.

when PSSR is weak, and to better understandthe complexities of the underlying physics.

Published: 2018/4/14
https://doi.org/10.1186/s40645-018-0179-4― 18 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Effects of the postsunset vertical plasma drift on the generation of equatorial spread F
Huang C-S
[Keywords] Equatorial ionosphere, Equatorial spread F, Plasma bubbles, Rayleigh-Taylor instability, Vertical plasma
drift, Prereversal enhancement

Equatorial spread F (ESF) irregularities arecaused by plasma instability processes in theequatorial ionosphere and especially related
to plasma bubble phenomena in the topside F
region. Plasma bubbles result from nonlinear
evolution of the Rayleigh-Taylor instability. The
prereversal enhancement (PRE) of the postsunset vertical plasma drift increases the heightThe dependence of the plasma bubble occurrence probability on the verti-of the equatorial F layer, creating conditions

cal ion drift at the PRE peak measured by C/NOFS during May 2008-June

conducive to the growth of the Rayleigh-Taylor

2013 for different seasons.

instability, and is an important factor that controls the generation of ESF. Three different relationships of the quantitative connection between the PRE and ESF
occurrence have been derived. (1) A threshold PRE must be reached for the occurrence of ESF. ESF will be generated
when the PRE is larger than the threshold and will not be generated when the PRE is smaller than the threshold. (2)The occurrence probability of ESF increases approximately linearly with the PRE. (3) The occurrence probability of
ESF is characterized by a continuous probability distribution as a function of the PRE magnitude. The second and third
relationships imply that the PRE can be used to specify the occurrence probability of ESF. This paper will review these
relationships and discuss how these relationships are connected to each other. The effects of seeding perturbations
on the generation and global distribution of ESF will be briefly discussed.

Published: 2018/1/9
https://doi.org/10.1186/s40645-017-0155-4― 19 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

A review on the numerical simulation of equatorial plasma bubbles toward scintillation evaluationand forecasting
Yokoyama T[Keywords] Equatorial ionosphere, Equatorial spread F, Equatorial plasma bubbles, Numerical simulation, Scintillation,
High-performance computing, Space weather

Equatorial plasma bubbles (EPBs) have beena longstanding and increasingly important subject because they cause severe scintillations inradio waves from Global Navigation Satellite
System satellites. The phenomenon was foundin the 1930s as irregular ionosonde observations and was termed equatorial spread F (ESF).
ESF is interpreted as plasma density irregularities associated with EPBs that have nonlinearly
evolved into the topside ionosphere. Numericalsimulations have been powerful tools to study
the fully nonlinear evolution of EPBs, whichcannot be wholly understood from theoreticalpredictions. In this paper, historical achievements in the numerical simulation of EPBs arereviewed, and future directions toward scintillation evaluation and forecast are discussed.

An example of numerical simulation results of equatorial plasma bubbles

Published: 2017/12/12
https://doi.org/10.1186/s40645-017-0153-6― 20 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Mars core structure — concise review and anticipated insights from InSight
Helffrich G[Keywords] Mars, InSight, Dynamo, Core, Fe-FeS phase relations, Stratification

This review summarizes the knowledge ofMars’ interior structure, its inferred composition, and the anticipated seismological properties arising from its composition with particularfocus on Mars’ core. The emphasis on the corestems from the unusual morphology of the liquidus diagram of iron at moderate pressureswhen enriched in sulfur. From a fairly detailed
liquidus diagram constructed from experimental
studies, I identify a set of processes that could
act within Mars’ core: an iron “snow” from thecore-mantle boundary’s surface and a Fe3-xS2“ground fog” forming at the base of the core.
Depending on temperature and bulk sulfur
composition, these could form an inner core or
could stratify the outer core by enriching it insulfur, or both. Core stratification could be one
explanation for the extinction of Mars’ magnetic
field early in the planet’s history, and I demon-

Comparison of sizes and interior features of Earth and Mars. Mars is

strate the feasibility of this mechanism. The

almost a half-size scale model of the Earth, except for its thicker crust

crystallization processes in the core could be(Rivoldini et al., 2011) and its probable absence of an inner core. Core,observable in the seismic data that the future

Fe-FeS phase relations, Stratification

Mars geophysical mission, InSight, is planned
to provide. The core size, the presence of an inner core, and the wavespeed profile of the outer core, whose radialderivative provides a proxy for changes in composition, are key observables to seek.

Published: 2017/9/6
https://doi.org/10.1186/s40645-017-0139-4― 21 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Extreme geomagnetically induced currents
Kataoka R, Ngwira C[Keywords] Geomagnetically induced currents, Magnetic storms, Auroral substorms, Sudden commencements, Solarenergetic particles

We propose an emergency alert frameworkfor geomagnetically induced currents (GICs),
based on the empirically extreme values andtheoretical upper limits of the solar wind parameters and of dB/dt, the time derivative of magnetic field variations at ground. We expect thisframework to be useful for preparing against
extreme events. Our analysis is based on areview of various papers, including those presented during Extreme Space Weather Workshops held in Japan in 2011, 2012, 2013, and2014. Large-amplitude dB/dt values are themajor cause of hazards associated with threedifferent types of GICs: (1) slow dB/dt with ring
current evolution (RC-type), (2) fast dB/dt associated with auroral electrojet activity (AE-type),

Emergency alert framework for geomagnetically induced currents. The
equatorward boundary of the auroral oval according to the model of
Yokoyama et al. (1998) is shown by the solid curve, and the dotted curveand (3) transient dB/dt of sudden commence-shows its theoretical extrapolation. It is important to update the possible

ments (SC-type). We set “caution,” “warning,”

extension of the auroral oval toward middle to low latitudes during extremeand “emergency” alert levels during the main

magnetic storms.

phase of superstorms with the peak Dst index ofless than −300 nT (once per 10 years), −600 nT (once per 60 years), or −900 nT (once per 100 years), respectively.
The extreme dB/dt values of the AE-type GICs are 2000, 4000, and 6000 nT/min at caution, warning, and emergency
levels, respectively. For the SC-type GICs, a “transient alert” is also proposed for dB/dt values of 40 nT/s at low latitudes and 110 nT/s at high latitudes, especially when the solar energetic particle flux is unusually high.

Published: 2016/8/19
https://doi.org/10.1186/s40645-016-0101-x― 22 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Magnetohydrodynamics Modeling of Coronal Magnetic Field and Solar Eruptions Based on the
Photospheric Magnetic Field
Inoue S
[Keywords] Sun; Magnetic Field, Photosphere, Corona, Magnetohydrodynamics (MHD), Solar Active Region, Solar
Flare, Coronal Mass Ejection (CME)

In this paper, we summarize current progress on using the observed magnetic fields formagnetohydrodynamics (MHD) modeling of
the coronal magnetic field and of solar eruptions, including solar flares and coronal massejections (CMEs). Unfortunately, even with theexisting state-of-the-art solar physics satellites,
only the photospheric magnetic field can bemeasured. We first review the 3D extrapolationof the coronal magnetic fields from measurements of the photospheric field. Specifically, we
focus on the nonlinear force-free field (NLFFF)
approximation extrapolated from the three components of the photospheric magnetic field.
On the other hand, because in the force-free
approximation the NLFFF is reconstructed forThree-dimensional dynamics of the flux tube during an X2.2-class flareequilibrium states, the onset and dynamics ofobtained from our MHD simulation; the field lines with more (less) thansolar flares and CMEs cannot be obtained fromone-turn at t=0 are depicted in orange (blue). The Bz distribution is shownthese calculations. Recently, MHD simulations
using the NLFFF as an initial condition havebeen proposed for understanding these dynam-

in red and blue. The inset at t=0 shows the top view of the field lines; thenumber of field lines with less than one turn has been reduced. Eventually,
the large highly twisted flux tube is formed through the magnetic reconnection between these twisted liens.

ics in a more realistic scenario. These results
have begun to reveal complex dynamics, some of which have not been inferred from previous simulations of hypothetical situations, and they have also successfully reproduced some observed phenomena. Although MHD simulations
play a vital role in explaining a number of observed phenomena, there still remains much to be understood. Herein,
we review the results obtained by state-of-the-art MHD modeling combined with the NLFFF.

Published: 2016/7/4
https://doi.org/10.1186/s40645-016-0084-7― 23 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

MF and HF radar techniques for investigating the dynamics and structure of the 50 to 110 km
height region: a review
Reid I M[Keywords] Medium-frequency radar techniques, High-frequency radar techniques, Partial reflection radar, Spaced
antenna technique, Full correlation analysis, Mesosphere lower thermosphere region, D region, MLT region dynamics,
Meteor radar, Imaging Doppler interferometer

The application of medium-frequency (MF)and high-frequency (HF) partial reflection radar
to investigate the neutral upper atmosphereis one of the oldest such techniques still regularly in use. The techniques have been continuously improved and remain a robust andreliable method of obtaining wind velocities,
turbulence intensities, electron densities, andmeasurements of atmospheric structure in themesosphere lower thermosphere (MLT) region

MF and HF radars used to measure the MLT region. Green indicates(50 to 110 km). In this paper, we review recent

retired radars, blue current radars, and yellow dynasondes that have oper-

developments, discuss the strengths and weak-ated as IDI radars. See text and Tables 2 and 3 for further details.

nesses of the technique, and consider possible
improvements.

Published: 2015/10/19
https://doi.org/10.1186/s40645-015-0060-7― 24 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Advancing the understanding of the Sun-Earth interaction - the Climate and Weather of the SunEarth System (CAWSES) II Program
Tsuda T, Shepherd M G, Gopalswamy N[Keywords] Coupled solar–terrestrial system, Solar activity, Space weather, Geospace, Atmospheric coupling, Trends,
Global warming, Paleoclimatology

The Scientific Committee on Solar–Terrestrial Physics (SCOSTEP) of the International
Council for Science (ICSU) implemented aninternational collaborative program called Climate and Weather of the Sun–Earth System(CAWSES), which was active from 2004 to
2008; this was followed by the CAWSES II
program during the period of 2009–2013. The
CAWSES program was aimed at improving theunderstanding of the coupled solar–terrestrial
system, with special emphasis placed on the
short-term (weather) and long-term (climate)variability of solar activities and their effects on

A schematic concept of CAWSES II with four task groups (TGs), E-scienceand responses of Geospace and Earth’s envi-

and capacity building.

ronment. Following the successful implementation of CAWSES, the CAWSES II program pursued four fundamental questions addressing the way in which thecoupled Sun–Earth system operates over time scales ranging from minutes to millennia, namely, (1) What are thesolar influences on the Earth’s climate? (2) How will Geospace respond to an altered climate? (3) How does shortterm solar variability affect the Geospace environment? and (4) What is the Geospace response to variable inputs
from the lower atmosphere? In addition to these four major tasks, the SCOSTEP and CAWSES promoted E-scienceand informatics activities including the creation of scientific databases and their effective utilization in solar–terrestrial
physics research. Capacity building activities were also enhanced during CAWSES II, and this represented an important contribution of SCOSTEP to the world’s solar–terrestrial physics community. This introductory paper provides an
overview of CAWSES II activities and serves as a preface to the dedicated review papers summarizing the achievements of the program’s four task groups (TGs) and the E-science component.

Published: 2015/9/17
https://doi.org/10.1186/s40645-015-0059-0― 25 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

The science case for the EISCAT_3D radar
McCrea I, Aikio A, Alfonsi L, Belova E, Buchert S, Clilverd M, Engler N, Gustavsson B, Heinselman C, KeroJ, Kosch M, Lamy H, Leyser T, Ogawa Y, Oksavik K, Pellinen-Wannberg A, Pitout F, Rapp M, Stanislawska
I, Vierinen J[Keywords] EISCAT, EISCAT_3D, Radar, Incoherent scatter, Atmospheric science, Space physics, Plasma physics,
Solar system research, Space weather, Radar techniques

The EISCAT (European Incoherent SCATer)
Scientific Association has provided versatileincoherent scatter (IS) radar facilities on themainland of northern Scandinavia (the EISCAT
UHF and VHF radar systems) and on Svalbard(the electronically scanning radar ESR (EISCAT
Svalbard Radar) for studies of the high-latitude
ionised upper atmosphere (the ionosphere).
The mainland radars were constructed about
30 years ago, based on technological solutions

Schematic representation showing the volumetric imaging of an ionospheric layer above Scandinavia by EISCAT_3D. (Image courtesy of EISCAT Scientific Association)of that time. The science drivers of today, however, require a more flexible instrument, which allows measurements to be made from the troposphere to the topside
ionosphere and gives the measured parameters in three dimensions, not just along a single radar beam. The possibility
for continuous operation is also an essential feature. To facilitate future science work with a world-leading IS radar
facility, planning of a new radar system started first with an EU-funded Design Study (2005–2009) and has continued
with a follow-up EU FP7 EISCAT_3D Preparatory Phase project (2010–2014). The radar facility will be realised byusing phased arrays, and a key aspect is the use of advanced software and data processing techniques. This type ofsoftware radar will act as a pathfinder for other facilities worldwide. The new radar facility will enable the EISCAT_3D
science community to address new, significant science questions as well as to serve society, which is increasingly
dependent on space-based technology and issues related to space weather. The location of the radar within theauroral oval and at the edge of the stratospheric polar vortex is also ideal for studies of the long-term variability inthe atmosphere and global change. This paper is a summary of the EISCAT_3D science case, which was preparedas part of the EU-funded Preparatory Phase project for the new facility. Three science working groups, drawn fromthe EISCAT user community, participated in preparing this document. In addition to these working group members,
who are listed as authors, thanks are due to many others in the EISCAT scientific community for useful contributions,discussions, and support.

Published: 2015/7/29
https://doi.org/10.1186/s40645-015-0051-8― 26 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Short-term variability of the Sun-Earth system: an overview of progress made during the
CAWSES-II period
Gopalswamy N, Tsurutani B, Yihua Y[Keywords] Solar activity, Space weather, Coronal mass ejections, Flares, Solar energetic particle events, Geospace
impact, Geomagnetic storms

This paper presents an overview of results
obtained during the CAWSES-II period on
the short-term variability of the Sun and how
it affects the near-Earth space environment.
CAWSES-II was planned to examine the behavior of the solar-terrestrial system as the solar
activity climbed to its maximum phase in solar
cycle 24. After a deep minimum following cycle
23, the Sun climbed to a very weak maximum
in terms of the sunspot number in cycle 24(MiniMax24), so many of the results presented
here refer to this weak activity in comparison
with cycle 23. The short-term variability that has
immediate consequence to Earth and geospace
manifests as solar eruptions from closed-fieldregions and high-speed streams from coronalholes. Both electromagnetic (flares) and mass

Speed vs. width distributions of limb CMEs from cycles 23 and 24. Bothcycles show a good correlation between speed and width, but the slopes
are very different. The correlations coefficients (r) and the regression lines

emissions (coronal mass ejections - CMEs)

are given on the plot. Student’s t-test confirms that the slope difference

are involved in solar eruptions, while coronalis statistically significant. The data points at width=360o are halo CMEs,

holes result in high-speed streams that collide

which are mostly from cycle 24.

with slow wind forming the so-called corotatinginteraction regions (CIRs). Fast CMEs affect Earth via leading shocks accelerating energetic particles and creatinglarge geomagnetic storms. CIRs and their trailing high-speed streams (HSSs), on the other hand, are responsible forrecurrent small geomagnetic storms and extended days of auroral zone activity, respectively. The latter leads to theacceleration of relativistic magnetospheric ‘killer’ electrons. One of the major consequences of the weak solar activity
is the altered physical state of the heliosphere that has serious implications for the shock-driving and storm-causing
properties of CMEs. Finally, a discussion is presented on extreme space weather events prompted by the 23 July 2012super storm event that occurred on the backside of the Sun. Many of these studies were enabled by the simultaneous
availability of remote sensing and in situ observations from multiple vantage points with respect to the Sun-Earth line.

Published: 2015/6/17
https://doi.org/10.1186/s40645-015-0043-8― 27 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

eScience and Informatics for International Science Programs
Fox P, Kozyra J[Keywords] eScience, Informatics, Virtual observatory, Virtual organization, Collaboration, Interdisciplinary research

Both eScience and Informatics, their conceptual approaches, methods, and extant technicalsolutions, are still relatively new approaches inmany science fields. Collectively, they intend
to facilitate the electronic conduct of science(eScience) and the application of foundational
principles drawn from experience in a numberof fields of Informatics (e.g., helioinformatics,
geoinformatics, and climateinformatics). The
Climate and Weather of the Sun-Earth System
II (CAWSES II) eScience and Informatics effort
had the goal of promoting an international virtual institute and several virtual observatories inorder to advance system-level science investigations aligned with the four CAWSES II Task
Groups. This contribution elaborates on the key
elements of eScience and Informatics applicable to CAWSES II as a virtual organization in the

CAWSES II program concept for virtual institute for collaborative knowl-

context of the current science-data landscape.

edge development

We examine what was adopted for CAWSESII and highlight the successes and challenges of the effort. Based on the lessons learned from this effort and otherinternational communities, we present opportunities going forward that are relevant to both smaller collaborations andsuccessor large-scale programs (such as the Variability of the Sun and Its Terrestrial Impact (VarSITI)) that are being
recognized more as networks of science facilitated by a variety of modern information technologies.

Published: 2015/5/19
https://doi.org/10.1186/s40645-015-0042-9― 28 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

What is the solar influence on climate? Overview of activities during CAWSES-II
Seppälä A, Matthes K, Randall C E, Mironova I A[Keywords] Climate, Atmosphere, Solar irradiance, Total solar irradiance, TSI, Solar spectral irradiance, SSI, Energetic
particles, EPP, Cosmic rays

This paper presents an overview of the main
advances in the Key Questions identified by
the Task Group ‘What is the Solar Influenceon Climate’ by the SCOSTEP CAWSES-II science program. We go through different aspectsof solar forcing from solar irradiance, including
total solar irradiance (TSI) and solar spectral
irradiance (SSI), to energetic particle forcing,including energetic particle precipitation (EPP)
and cosmic rays (CR). Besides discussing themain advances in the timeframe 2009 to 2013,
we also illustrate the proposed mechanism forclimate variability for the different solar variability sources listed above. The key questions are
as follows: What is the importance of spectral
variations to solar influences on climate? Whatis the effect of energetic particle forcing on the

Energetic particle precipitation (EPP) impact on the atmosphere. Main
direct and indirect impacts from EPP (including EEP and SPE). EPP ionisation is focused on the polar regions leading to production of HOx andNOx shown in the figure. Transport processes are shown with grey dottedwhole atmosphere and what are the implica-

lines, while coupling mechanisms are indicated with grey dashed lines.

tions for climate? How well do models repro-

Direct chemical impacts are shown with black arrows.

duce and predict solar irradiance and energetic
particle influences on the atmosphere and climate?

Published: 2014/11/26
https://doi.org/10.1186/s40645-014-0024-3― 29 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

Response of the mesosphere-thermosphere-ionosphere system to global change – CAWSES-II
contribution
Laštovička J, Beig G, Marsh D R[Keywords] Mesosphere, Thermosphere, Ionosphere, Long-term trends, Climatic change

Long-term trends in the mesosphere, thermosphere, and ionosphere are areas of researchof increasing importance both because they
are sensitive indicators of climatic change andbecause they affect satellite-based technologies which are increasingly important to modern life. Their study was an important part of
CAWSES-II project, as they were a topic of Task
Group 2 (TG-2) ‘How Will Geospace Respondto Changing Climate’. Three individual projectsof TG-2 were focused on important problems
in trend investigations. Significant progress wasreached in several areas such as understandingand quantifying the role of stratospheric ozone
changes in trends in the upper atmosphere,reaching reasonable agreement between
observed and simulated trends in mesospherictemperatures and polar mesospheric clouds, orunderstanding of why the thermospheric density trends are much stronger under solar cycle

Trends in the Earth’s atmosphere. The atmospheric layers are defined by
the temperature profile. The ionospheric layers are defined by the elec-

minimum conditions. The TG-2 progress thattron density profile (midnight at equator). Arrows indicate the direction ofis reviewed in this paper together with somechange. Red - warming, blue - cooling, green - no change of temperature,

results reached outside CAWSES-II so as toblack - changes in electron density (horizontal) and heights of ionospheric

have the full context of progress in trends inlayers (vertical).

the upper atmosphere and ionosphere.

Published: 2014/11/11
https://doi.org/10.1186/s40645-014-0021-6― 30 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Space and planetary sciences

The geospace response to variable inputs from the lower atmosphere: A review of the progress
made by Task Group 4 of CAWSES-II
Oberheide J, Kazuo S, Gurubaran S, Ward W E, Fujiwara H, Kosch M J, Makela J J, Takahashi H[Keywords] Geospace, Thermosphere, Ionosphere, Tides, Planetary waves, Gravity waves, Traveling ionosphericdisturbances, Traveling atmospheric disturbances

The advent of new satellite missions, groundbased instrumentation networks, and the development of whole atmosphere models over the
past decade resulted in a paradigm shift inunderstanding the variability of geospace, thatis, the region of the atmosphere between thestratosphere and several thousand kilometers above ground where atmosphere-ionosphere-magnetosphere interactions occur. It
has now been realized that conditions in geospace are linked strongly to terrestrial weather
and climate below, contradicting previous textbook knowledge that the space weather ofEarth’s near space environment is driven by

Sketch of meteorological impacts on geospace due to non-Sun-synchro-energy injections at high latitudes connectednous (nonmigrating) tides as observed by different satellites in various

with magnetosphere-ionosphere coupling andneutral and plasma parameters. The COSMIC figure is adapted withsolar radiation variation at extreme ultraviolet
wavelengths alone. The primary mechanism

permission from Lin et al. (2007), the IMAGE figure is adapted withpermission from Immel et al. (2006), the TIMED figure uses data from
Oberheide et al. (2006), and the SNOE figure is adapted with permission

through which energy and momentum are trans-

from Oberheide and Forbes (2008). Deep convective cloud data are fromferred from the lower atmosphere is throughthe ISCCP climatology. CHAMP neutral density data are provided by Dr

the generation, propagation, and dissipation of

X. Zhang and Dr. S. L. Bruinsma.

atmospheric waves over a wide range of spatial
and temporal scales including electrodynamic coupling through dynamo processes and plasma bubble seeding. The
main task of Task Group 4 of SCOSTEP’s CAWSES-II program, 2009 to 2013, was to study the geospace response
to waves generated by meteorological events, their interaction with the mean flow, and their impact on the ionosphereand their relation to competing thermospheric disturbances generated by energy inputs from above, such as auroral
processes at high latitudes. This paper reviews the progress made during the CAWSES-II time period, emphasizing
the role of gravity waves, planetary waves and tides, and their ionospheric impacts. Specific campaign contributions
from Task Group 4 are highlighted, and future research directions are discussed.

Published: 2014/2/11
https://doi.org/10.1186/s40645-014-0031-4― 31 ―

Review
Atmospheric and hydrospheric sciences

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

The response of the hydrological cycle to temperature changes in recent and distant climatic
history
Shailendra Pratap, Yannis Markonis[Keywords] Global water cycle, Paleoclimate, Hydrological cycle, Water cycle intensification, Hydroclimatic variability

The relationship between the hydrologicalcycle and the temperature is rather complex
and of great importance to human socioeconomic activities. The prevailing theory suggeststhat as temperature increases the hydrologicalcycle is intensified. Practically, this means more
and heavier precipitation. However, the exact
magnitude of hydrological cycle response andits spatio-temporal characteristics is still underinvestigation. Looking back in Earth’s hydroclimatic history, it is easy to find some periods
where global temperature was substantially different than present. Here, we examine some ofthese periods to present the current knowledge about past hydrological cycle variability (specifically precipitation), andits relationship to temperature. The periods under investigation are the Mid-Miocene Climate Optimum, the EemianInterglacial Stage, the Last Glacial Maximum, the Heinrich and Dansgaard–Oeschger Events, the Bølling–Allerød, theYounger Dryas, the 8.2 ka event, the Medieval Climate Anomaly, and the Little Ice Age. We report that the hypothesisthat a warmer climate is a wetter climate could be an oversimplification, because the response of water cycle appears
to be spatio-temporally heterogeneous.

Published: 2022/5/31
https://doi.org/10.1186/s40645-022-00489-0― 34 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Marine microplastics as vectors of major ocean pollutants and its hazards to the marine ecosystem and humans
Tan Suet May Amelia, Wan Mohd Afiq Wan Mohd Khalik, Meng Chuan Ong, Yi Ta Shao, Hui-Juan Pan,
Kesaven Bhubalan[Keywords] Adsorption, Bioaccumulation, Contaminant, Microplastic, Pollutant, Vector

Microplastic pollutes water, land, air, andgroundwater environments not only visually
but also ecologically for plants, animals, andhumans. Microplastic has been reported toact as vectors by sorbing pollutants and contributing to the bioaccumulation of pollutants,
particularly in marine ecosystems, organisms,
and subsequently food webs. The inevitable exposure of microplastic to humans emphasises the need to review thepotential effects, exposure pathways, and toxicity of microplastic toward human health. Therefore, this review wasaimed to reveal the risks of pollutant sorption and bioaccumulation by microplastic toward humans, as well as thedominant types of pollutants sorbed by microplastic, and the types of pollutants that are bioaccumulated by microplastic
in the living organisms of the marine ecosystem. The possible factors influencing the sorption and bioaccumulationof pollutants by microplastic in marine ecosystems were also reviewed. The review also revealed the prevailing typesof microplastic, abundance of microplastic, and geographical distribution of microplastic in the aquatic environment
globally. The literature review revealed that microplastic characteristics, chemical interactions, and water properties
played a role in the sorption of pollutants by microplastic. The evidence of microplastic posing a direct medical threat
to humans is still lacking albeit substantial literature has reported the health hazards of microplastic-associated monomers, additives, and pollutants. This review recommends future research on the existing knowledge gaps in microplastic research, which include the toxicity of microplastic, particularly to humans, as well as the factors influencing
the sorption and bioaccumulation of pollutants by microplastic.

Published: 2021/1/22
https://doi.org/10.1186/s40645-020-00405-4― 35 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Applications of soft computing models for predicting sea surface temperature: a comprehensive
review and assessment
Masoud Haghbin, Ahmad Sharafati, Davide Motta, Nadhir Al-Ansari, Mohamadreza Hosseinian Moghadam
Noghani[Keywords] Soft computing, Sea Surface Temperature, Prediction

The application of soft computing (SC) models
for predicting environmental variables is widely
gaining popularity, because of their capability
to describe complex non-linear processes. The
sea surface temperature (SST) is a key quantity in the analysis of sea and ocean systems,
due to its relation with water quality, organisms,
and hydrological events such as droughts andfloods. This paper provides a comprehensive
review of the SC model applications for estimating SST over the last two decades. Types of model (based on artificial neural networks, fuzzy logic, or other SC
techniques), input variables, data sources, and performance indices are discussed. Existing trends of research in thisfield are identified, and possible directions for future investigation are suggested.

Published: 2021/1/5
https://doi.org/10.1186/s40645-020-00400-9― 36 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Two decades of Earth system modeling with an emphasis on Model for Interdisciplinary
Research on Climate (MIROC)
Michio Kawamiya, Tomohiro Hajima, Kaoru Tachiiri, Shingo Watanabe, Tokuta Yokohata[Keywords] Earth system model, Climate change, IPCC, Carbon cycle, Biogeochemistry, Interdisciplinary project,
Remaining carbon budget, Socioeconomics, Nitrogen, Iron.

The past 20 years of research using Earthsystem models (ESMs) is reviewed with anemphasis on results from the ESM based on
MIROC (Model for Interdisciplinary Researchon Climate) developed in Japan. Earth system models are climate models incorporating
biogeochemical processes such as the carbon
cycle. The development of ESM was triggered bystudies of the feedback between climate change
and the carbon cycle. State-of-the-art ESMs aremuch more realistic than the first ESMs. They
now include various biogeochemical processes
other than carbon, such as atmospheric chemistry and the nitrogen and iron cycles as wellas nutrient transport by atmospheric dust andrivers. They are used to address many prac-

Conceptual diagram of Earth system model (ESM) projections oftical issues, such as evaluating the amount of

global change: Anthropogenic greenhouse gas emissions and nitrogencarbon dioxide emissions that is consistent with

fixation are increasing; ESMs can model interactions between climate

climate change mitigation targets, and are indis-change and biogeochemical cycles.

pensable tools for the development of climatechange mitigation policies. Novel, ambitious attempts to use ESMs include coupling socioeconomics with Earth systems, and projecting the carbon cycle on decadal timescales. Development of ESMs requires ongoing integration ofmultiple aspects of climate science. Emerging applications of ESMs can bring forth meaningful insights, and should
be directed toward expanding connections with fields outside climate science, e.g., socioeconomics.

Published: 2020/10/20
https://doi.org/10.1186/s40645-020-00369-5― 37 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

d4PDF: large-ensemble and high-resolution climate simulations for global warming risk assessment
Masayoshi Ishii, Nobuhito Mori
[Keywords] Global warming, d4PDF, ensemble climate simulation, atmospheric model, dynamical downscaling,detection and attribution, impact assessment, climate change adaptation, natural hazard, storm surge

A large-ensemble climate simulation database, which is known as the database for policy decision-making for future climate changes(d4PDF), was designed for climate change risk
assessments. Since the completion of the first
set of climate simulations in 2015, the databasehas been growing continuously. It contains theresults of ensemble simulations conducted
over a total of thousands years respectively forpast and future climates using high-resolution
global (60 km horizontal mesh) and regional(20 km mesh) atmospheric models. Several
sets of future climate simulations are available,
in which global mean surface air temperatures
are forced to be higher by 4 K, 2 K, and 1.5 K
relative to preindustrial levels. Nonwarming past
climate simulations are incorporated in d4PDF
along with the past climate simulations. The
total data volume is approximately 2 petabytes.

Time series of global mean surface air temperature anomalies of d4PDF

The atmospheric models satisfactorily simulate

for past (light blue), nonwaming (blue), +1.5 K (green), +2 K (orange), andthe past climate in terms of climatology, natural+4 K (red) climate simulations and CMIP5 historical and RCP8.5 experi-

variations, and extreme events such as heavy
precipitation and tropical cyclones. In addition,
data users can obtain statistically significant

ments with six climate models. Shading indicates two-sigma uncertainties.
Time series are drawn relative to the averages for the period from 1975
to 2005.

changes in mean states or weather and climate extremes of interest between the past and future climates via a
simple arithmetic computation without any statistical assumptions. The database is helpful in understanding futurechanges in climate states and in attributing past climate events to global warming. Impact assessment studies forclimate changes have concurrently been performed in various research areas such as natural hazard, hydrology,
civil engineering, agriculture, health, and insurance. The database has now become essential for promoting climate
and risk assessment studies and for devising climate adaptation policies. Moreover, it has helped in establishing aninterdisciplinary research community on global warming across Japan.

Published: 2020/10/7
https://doi.org/10.1186/s40645-020-00367-7― 38 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

DYAMOND: The DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic
Domains
Stevens B, Satoh M, Auger L, Biercamp J, Bretherton CS, Chen X, Duben P, Judt F, Khairoutdinov M, Klocke
D, Kodama C, Kornblueh L, Lin SJ, Neumann P, Putman WM, Rober N, Shibuya R, Vanniere B, Vidale PL,
Wedi N, Zhou L[Keywords] Climate modelling, Model intercomparison project, Tropical Convection

A review of the experimental protocol andmotivation for DYAMOND, the first intercomparison project of global storm-resolving models,is presented. Nine models submitted simulation
output for a 40-day (1 August–10 September2016) intercomparison period. Eight of these
employed a tiling of the sphere that was uniformly less than 5 km. By resolving the transient
dynamics of convective storms in the tropics,
global storm-resolving models remove the needto parameterize tropical deep convection, providing a fundamentally more sound representation of the climate system and a more naturallink to commensurately high-resolution data

Snapshot of DYAMOND Models. Shown is a snapshot of the models takenfrom satellite-borne sensors. The models andfrom the perspective of the Himawari-8. The images are for the cloudsome basic characteristics of their output arescene on 4 August 2016, and are qualitatively rendered based on each

described in more detail, as is the availability

model’s condensate fields to illustrate the variety of convective structuresand planned use of this output for future sci-

resolved by the models, and difficulty of distinguishing them form actual

entific study. Tropically and zonally averagedenergy budgets, precipitable water distributions,and precipitation from the model ensemble areobservations. From left to right, the images are from IFS-4km, IFS-9km,
NICAM, and SAM (top row); Arpege, Himawari, and ICON (middle row);
FV3, GEOS5, UKMO and MPAS (bottom row).

evaluated, as is their representation of tropical
cyclones and the predictability of column water vapor, the latter being important for tropical weather.

Published: 2019/9/30
https://doi.org/10.1186/s40645-019-0304-z― 39 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Toward reduction of the uncertainties in climate sensitivity due to cloud processes using a global
non-hydrostatic atmospheric model
Satoh M, Noda A, Seiki T, Chen Y, Kodama C, Yamada Y, Kuba N, Sato Y[Keywords] NICAM, Cloud microphysics scheme, Cloud changes, Cloud feedback, Global non-hydrostatic model,
Global warming

In estimates of climate sensitivity obtained
from global models, the need to represent
clouds introduces a great deal of uncertainty.
To address this issue, approaches using ahigh-resolution global non-hydrostatic model arepromising: the model captures cloud structureby explicitly simulating meso-scale convective
systems, and the results compare reasonably
well with satellite observations. We review theoutcomes of a 5-year project aimed at reducing the uncertainty in climate models due tocloud processes using a global non-hydrostatic
model. In our project, which was conducted asa subgroup of the Program for Risk Information
on Climate Change, or SOUSEI, we use the non-hydrostatic icosahedral atmospheric model (NICAM) to study cloud
processes related to climate change. NICAM performs numerical simulations with much higher resolution (about 7
km or 14 km mesh) than conventional global climate models (GCMs) using cloud microphysics schemes without acumulus parameterization scheme, which causes uncertainties in climate projection.
The subgroup had three research targets: analyzing cloud changes in global warming simulations with NICAM withthe time-slice approach, sensitivity of the results to the cloud microphysics scheme employed, and evaluating circulation changes due to global warming. The research project also implemented a double-moment bulk cloud microphysics
scheme and evaluated its results using satellite observation, as well as comparing it with a bin cloud microphysics
scheme. The future projection simulations show in general increase in high cloud coverage, contrary to results withother GCMs. Changes in cloud horizontal-size distribution size and structures of tropical/extratropical cyclones canbe discussed with high resolution simulations. At the conclusion of our review, we also describe the future prospectsof research for global warming using NICAM in the program that followed SOUSEI, known as TOUGOU.

Published: 2018/10/29
https://doi.org/10.1186/s40645-018-0226-1― 40 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Maritime continent coastlines controlling Earth’s climate
Yamanaka MD, Ogino SY, Wu PM, Hamada JI, Mori S, Matsumoto J, Syamsudin F[Keywords] Indonesian maritime continent, Atmosphere–ocean–land interaction, Convective clouds, Multiple scales,
Diurnal cycle, Sea−land breeze circulation

During the Monsoon Asian Hydro−Atmosphere Scientific Research and Prediction Initiative (MAHASRI; 2006–16), we carried out
two projects over the Indonesian maritime continent (IMC), constructing the Hydrometeorological Array for Intraseasonal Variation−Monsoon
Automonitoring (HARIMAU; 2005–10) radar
network and setting up a prototype institute for

Maritime-continental diurnal-cycle rain and latent heat controlling global

climate studies, the Maritime Continent Centerclimateof Excellence (MCCOE; 2009–14). Here, we
review the climatological features of the world’s largest “regional” rainfall over the IMC studied in these projects. The
fundamental mode of atmospheric variability over the IMC is the diurnal cycle generated along coastlines by land−seatemperature contrast: afternoon land becomes hotter than sea by clear-sky insolation before noon, with the opposite
contrast before sunrise caused by evening rainfall-induced “sprinkler”-like land cooling (different from the extratropicalinfrared cooling on clear nights). Thus, unlike the extratropics, the diurnal cycle over the IMC is more important in
the rainy season. The intraseasonal, seasonal to annual, and interannual climate variabilities appear as amplitude
modulations of the diurnal cycle. For example, in Jawa and Bali the rainy season is the southern hemispheric summer, because land heating in the clear morning and water vapor transport by afternoon sea breeze is strongest in
the season of maximum insolation. During El Niño, cooler sea water surrounding the IMC makes morning maritime
convection and rainfall weaker than normal. Because the diurnal cycle is almost the only mechanism generating
convective clouds systematically near the equator with little cyclone activity, the local annual rainfall amount in thetropics is a steeply decreasing function of coastal distance (e-folding scale 100–300 km), and regional annual rainfall
is an increasing function of “coastline density” (coastal length/land area) measured at a horizontal resolution of 100
km. The coastline density effect explains why rainfall and latent heating over the IMC are twice the global mean
for an area that makes up only 4% of the Earth’s surface. The diurnal cycles appearing almost synchronously over
the whole IMC generate teleconnections between the IMC convection and the global climate. Thus, high-resolution(<<100 km; <<1 day) observations and models over the IMC are essential to improve both local disaster prevention
and global climate prediction.

Published: 2018/4/4
https://doi.org/10.1186/s40645-018-0174-9― 41 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Outcomes and challenges of global high-resolution non-hydrostatic atmospheric simulations
using the K computer
Satoh M, Tomita H, Yashiro H, Kajikawa Y, Miyamoto Y, Yamaura T, Miyakawa T, Nakano M, Kodama C, Noda
A T, Nasuno T, Yamada Y, Fukutomi Y[Keywords] K computer, NICAM, intra-seasonal oscillations, Madden-Julian oscillation, tropical cyclone, global nonhydrostatic modelThis article reviews the major outcomes of a
5-year (2011–2016) project using the K computer to perform global numerical atmosphericsimulations based on the non-hydrostatic icosahedral atmospheric model (NICAM). The K
computer was made available to the public in
September 2012 and was used as a primaryresource for Japan’s Strategic Programs forInnovative Research (SPIRE), an initiative toinvestigate five strategic research areas; theNICAM project fell under the research area ofclimate and weather simulation sciences. Combining NICAM with high-performance computing
has created new opportunities in three areasof research: (1) higher resolution global simulations that produce more realistic representa-

Resolution dependencies of simulated cloud distribution: mesh size 14km, 3.5 km, and 870 m.

tions of convective systems, (2) multi-member
ensemble simulations that are able to perform extended-range forecasts 10–30 days in advance, and (3) multi-decadalsimulations for climatology and variability. Before the K computer era, NICAM was used to demonstrate realistic simulations of intra-seasonal oscillations including the Madden-Julian oscillation (MJO), merely as a case study approach.
Thanks to the big leap in computational performance of the K computer, we could greatly increase the number ofcases of MJO events for numerical simulations, in addition to integrating time and horizontal resolution. We conclude
that the high-resolution global non-hydrostatic model, as used in this five-year project, improves the ability to forecast
intra-seasonal oscillations and associated tropical cyclogenesis compared with that of the relatively coarser operationalmodels currently in use. The impacts of the sub-kilometer resolution simulation and the multi-decadal simulations
using NICAM are also reviewed.

Published: 2017/4/28
https://doi.org/10.1186/s40645-017-0127-8― 42 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

A review of atmospheric chemistry observation at mountain sites
Okamoto S, Tanimoto H[Keywords] Atmospheric observation, High-altitude station, Long-range transport, Seasonal cycle, Long-term trend,
Biomass burning, Anthropogenic pollution

Located far from anthropogenic emission
sources, high-altitude mountain stations are
considered to be ideal sites for monitoring climatic and environmentally important baselinechanges in free tropospheric trace gases andaerosols. In addition, the observations taken
at these stations are often used to study thelong-range transport of dust as well as anthropogenic and biomass burning pollutants fromsource regions and to evaluate the performanceof global and regional models. In this paper, wesummarize the results from past and ongoing
field measurements of atmospheric constituentsat high-altitude stations across the globe, withparticular emphasis on reactive trace species
including tropospheric ozone, along with its

Map showing the distribution of high-altitude mountain stations discussed

precursors such as carbon monoxide, nitrogenin this paper. Circles with abbreviations denote stations providing the dataoxides, total reactive nitrogen, and nonmeth-presented in this paper. ASK Assekrem, CHA Chiricahua NM, CMN Monteane hydrocarbons. Over the past decades,

Cimone, GRB Great Basin NP, HPO Mt. Happo, ISK Issyk-Kul, IZO Izãna,

our understanding of the temporal variability

JFJ Jungfraujoch, KVV Krvavec, LAV Lassen Volcanic NP, LLN Lulin, LQO

and meteorological mechanisms of long-range
transport has advanced in tandem with prog-

La Quiaca Observatorio, MBO Mt. Bachelor Observatory, MKN Mt. Kenya,
MDY Mondy, MLO Mauna Loa, NWR Niwot Ridge, PMO Pico Mountain
Observatory, PYR Nepal Climate Observatory–Pyramid, SNB Sonnblick,ress in instrumentation and modeling. Finally,

TAR Tanah Rata, WHI Whistler Mountain, WLG Mt. Waliguan, YEL Yel-the future needs of atmospheric chemistry

lowstone NP, YOS Yosemite NP, ZSF Zugspitze–Schneefernerhaus, ZUG

observations at mountain sites are addressed.

Zugspitze–Gipfel. Triangles with abbreviations denote stations for whichdata are not presented but are reviewed in this paper. ARO Arosa, FWS
Mt. Fuji, KSL Kislovodsk.

Published: 2016/10/26
https://doi.org/10.1186/s40645-016-0109-2― 43 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

A review of progress towards understanding the transient global mean surface temperature
response to radiative perturbation
Yoshimori M, Watanabe M, Shiogama H, Oka A, Abe-Ouchi A, Ohgaito R, Kamae Y[Keywords] Transient climate response, Equilibrium climate sensitivity, Climate feedback, Ocean heat uptake efficacy,
Efficacy of forcing

The correct understanding of the transient
response to external radiative perturbation isimportant for the interpretation of observed
climate change, the prediction of near-futureclimate change, and committed warming underclimate stabilization scenarios, as well as theestimation of equilibrium climate sensitivity
based on observation data. It has been known
for some time that the radiative damping rate
per unit of global mean surface temperature
increase varies with time, and this inconstancy
affects the transient response. Knowledge ofthe equilibrium response alone is insufficient,but understanding the transient response ofRelation between global mean surface air temperature and top-of-the-at-

the global mean surface temperature has mademosphere net radiation changes from the preindustrial control simulation

rapid progress. The recent progress accompa-

in the MIROC3.2 (medres) atmosphere-ocean general circulation model

nies the relatively new concept of the efficacies

experiments. Black crosses: 1pctCO2 experiment (every year for 1-140

of ocean heat uptake and forcing. The ocean

years); blue crosses: abrutp4xCO2 experiment (every year for 1-150

heat uptake efficacy associates the tempera-

years), red crosses: const4xCO2 experiment (every 20-year average forture response induced by ocean heat uptake
with equilibrium temperature response, and theefficacy of forcing compares the temperature
response caused by non-CO2 forcing with that141-3680 years); blue line: linear regression for the 150-year abrupt4xCO2
experiment; Blue circles: equilibrium temperature response to 4xCO2 estimated by Gregory’s method for 10 abrupt4xCO2 20-year-long ensemble
experiments (that start from different initial conditions in the preindustrial
control simulation).

by CO2 forcing.
In this review article, recent studies on these efficacies are discussed, starting from the classical global feedback
framework and basis of the transient response. An attempt is made to structure different studies that emphasize different aspects of the transient response and to stress the relevance of those individual studies. The implications on thedefinition and computation of forcing and on the estimation of the equilibrium response in climate models are also discussed. Along with these discussions, examples are provided with MIROC climate model multi-millennial simulations

Published: 2016/7/18
https://doi.org/10.1186/s40645-016-0096-3― 44 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Overview of the development of the Aerosol Loading Interface for Cloud microphysics In Simulation (ALICIS)
Iguchi T, Choi I-J, Sato Y, Suzuki K, Nakajima T[Keywords] Cloud microphysics, Cloud and aerosol, Regional modeling, Dynamical downscaling

This review summarizes the scientific background of and past/prospective update strategies for the development of the Aerosol Loading
Interface for Cloud microphysics In Simulation(ALICIS). ALICIS provides a novel approach forcoupling downscaled mesoscale cloud-resolving simulations to large-scale aerosol-transport
simulations. Realistic aerosol loading, including
spatio-temporal aerosol variations and particle-size spectra, is implemented in the cloud-resolving simulations. Prior studies employing

Conceptual diagram of the coupling framework between a large-scale

ALICIS have demonstrated how the interface

aerosol transport model and a regional-scale cloud resolving model using

introduction significantly improves the repro-

the ALICIS module.

ducibility of the simulated microphysical cloud
structure through better representation of aerosol effects on cloud.

Published: 2015/12/11
https://doi.org/10.1186/s40645-015-0075-0― 45 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

The dynamics of the mesosphere and lower thermosphere: a brief review
Vincent R A[Keywords] Atmospheric tides, Gravity waves, Planetary waves, Middle atmosphere, Mesosphere, Lower
thermosphere, Wave coupling

The dynamics of the mesosphere-lower thermosphere (MLT) (60 to 110 km) is dominated bywaves and their effects. The basic structure of
the MLT is determined by momentum deposition
by small-scale gravity waves, which drives asummer-to-winter pole circulation at the mesopause. Atmospheric tides are also an importantcomponent of the dynamics of the MLT. Observations from extended ground-based networks,
satellites as well as numerical modelling showthat non-migrating tidal modes in the MLT are
more important than previously thought, withevidence for directly coupling into the thermosphere/ionosphere. Major disturbances lower
in the atmosphere, such as wintertime sudden
stratospheric warmings, temporarily disrupt

The 2006 major sudden warming. Top: time-height cross-section of temperatures during the major SSW in late January 2006. Note the descentand disappearance of the stratopause at the peak of the warming and its

the circulation pattern and thermal structure ofsubsequent reappearance and descent from the mesosphere. Bottom:

the MLT. In the equatorial mesosphere, gravity

the time variation of the zonal-mean zonal wind at 10 hPa and 60 N. The

wave driving leads to oscillations in the zonal

blue line shows the wind during the stratwarm, while the red line depicts

wind on semiannual time scales, although

the climatalogical seasonal cycle. Adapted from Figure one of Yamazaki

variability on quasi-biennial time scales is also
apparent. Planetary-scale waves such as theet al. (2012).
Stratospheric warmings occur when large-scale planetary waves break inthe middle atmosphere (10-100 km) in winter. This figure shows that thequasi-two-day wave temporarily dominate thewhole middle atmosphere is affected, so that the EW (zonal) winds anddynamics of the summertime MLT, especially inthe temperature structure temporarily revert to summer-like conditions.

the southern hemisphere. Impacts may include

The zonal means winds in the stratosphere (blue line in bottom figure)short-term changes to the thermal structure

become westward (negative) for a short time while those above 70 km

and physics of the high-latitude MLT. Here, we(the mesosphere) become eastward. In turn, this change in the prevailingbriefly review the dynamics of the MLT, with aparticular emphasis on developments in thepast decade.

wind affects the vertical propagation of atmospheric gravity waves andchanges their impact on the middle atmosphere. The effects of stratospheric warmings can also be observed in the ionosphere, impacting onradiowave propagation.

Published: 2015/3/18
https://doi.org/10.1186/s40645-015-0035-8― 46 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

Modeling in Earth system science up to and beyond IPCC AR5
Hajima T, Kawamiya M, Watanabe M, Kato E, Tachiiri K, Sugiyama M, Watanabe S, Okajima H, Ito A[Keywords] Earth system science, Earth system model, Carbon and nitrogen cycle, Land and ocean CO2 uptake,
Ocean acidification, Land-use and land-cover change, EMICs, Geoengineering, Iron deposition

Changes in the natural environment that are
the result of human activities are becoming evident. Since these changes are interrelated andcan not be investigated without interdisciplinary
collaboration between scientific fields, Earthsystem science (ESS) is required to provide
a framework for recognizing anew the Earthsystem as one composed of its interacting subsystems. The concept of ESS has been partially realized by Earth system models (ESMs).
In this paper, we focus on modeling in ESS,

Schematic diagram of Earth system models

review related findings mainly from the latest
assessment report of the Intergovernmental Panel on Climate Change, and introduce tasks under discussion for the
next phases of the following areas of science: the global nitrogen cycle, ocean acidification, land-use and land-coverchange, ESMs of intermediate complexity, climate geoengineering, ocean CO2 uptake, and deposition of bioavailable
iron in marine ecosystems. Since responding to global change is a pressing mission in Earth science, modeling willcontinue to contribute to the cooperative growth of diversifying disciplines and expanding ESS, because modelingconnects traditional disciplines through explicit interaction between them.

Published: 2014/12/18
https://doi.org/10.1186/s40645-014-0029-y― 47 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Atmospheric and hydrospheric sciences

The Non-hydrostatic Icosahedral Atmospheric Model: Description and Development
Satoh M, Tomita H, Yashiro H, Miura H, Kodama C, Seiki T, Noda A, Yamada Y, Goto D, Sawada M, Miyoshi
T, Niwa Y, Hara M, Ohno Y, Iga S, Arakawa T, Inoue T, Kubokawa H[Keywords] Global non, hydrostatic model, Icosahedral grid, Global cloud-resolving simulations

This article reviews the development of a
global non-hydrostatic model, focusing on thepioneering research of the Non-hydrostatic Icosahedral Atmospheric Model (NICAM). Veryhigh resolution global atmospheric circulation
simulations with horizontal mesh spacing ofapproximately O (km) were conducted using
recently developed supercomputers. Thesetypes of simulations were conducted with a
specifically designed atmospheric global model
based on a quasi-uniform grid mesh structure
and a non-hydrostatic equation system. This
review describes the development of each
dynamical and physical component of NICAM,
the assimilation strategy and its related models,and provides a scientific overview of NICAM
studies conducted to date.
Icosahedral grids for grid division levels of 3, 4, and 5 (from left to right)(horizontal mesh spacings of approximately 893, 446 and 223 km).
Cloud distribution simulated by the NICAM 870 m grid spacing experiment.

Published: 2014/10/14
https://doi.org/10.1186/s40645-014-0018-1― 48 ―

Review
Human geosciences
Biogeosciences

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Human geosciences

Geomorphological processes and their connectivity in hillslope, fluvial, and coastal areas in
Bangladesh: A review
B. M. Refat Faisal, Yuichi S. Hayakawa[Keywords] Ganges-Brahmaputra-Meghna (GBM), Bangladesh, Satellite remote sensing, Fluvial processes, Sediment
dispersal, Landslides, Coastal erosion

Geomorphological knowledge is critical inunderstanding watershed scale surface processes, including steep mountainous areas andflat lowlands, particularly if the mid- and downstream areas are densely populated and hazard
assessments are highly required. However, ourknowledge about such surface processes has
relatively been limited in some areas in South
Asia due likely to the lack of comprehensive
studies of geomorphology and related fields.
This article undertakes an overview of the geomorphological processes of the disaster-pronedeltaic landscape of the Ganges–Brahmaputra–
Meghna (GBM), particularly focusing on fluvial

An overview of geomorphic connectivity in the Ganges-Brahmaputra Basinprocesses. The area locates in the downstream

with a focus on Bangladesh in the downstream domainof the watershed system including Himalayan
Mountains and highly connected with the upper basin morphodynamics, hydrology, and sediment flux. The previous
studies are summarized at different geomorphic settings concerning hillslopes, fluvial plains, and coastal areas toprovide clarity about the geomorphic processes linking erosion-prone upstream source areas to deposition-dominateddownstream areas. The review found that most of the geomorphic researches in Bangladesh are exploring landslide
inventory and susceptibility mapping in hilly areas; river channel or riverbank shifting, riverbank erosion and accretionin fluvial environments; watershed morphometric analysis and geomorphic unit identification in plain land; and coastline shifting or coastal erosion and accretion in coastal environments at a small scale. Then, we discuss the fluvial
dynamics and sediment transport of the GBM river system to address the knowledge gap in the context of deltaic
plain land in Bangladesh, where upstream fluvial sedimentation processes impact the geomorphic connectivity from
Himalayan to the Bay of Bengal. Although some studies on the fluvial dynamics and sediment dispersal in the upstream
GBM river basin are present, the fluvial processes in the downstream domain of Bangladesh are not fully understoodwith a limited number of research with field-based approaches. Some future perspectives of geomorphic researchin Bangladesh are then mentioned to understand better the complex geomorphological settings in the entire GBM
watershed and to strengthen the existing research capacity. This review will also develop a holistic understanding offluvial geomorphic processes of the GBM River to the policymakers and may be helpful to improve the transboundary
river basin management policies or strategies.

Published: 2022/7/25
https://doi.org/10.1186/s40645-022-00500-8― 50 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Human geosciences

A Review of Theoretical Salt Weathering Studies for Stone Heritage
Oguchi, C. T., Swe Yu[Keywords] Salt weathering theories, Crystal growth pressure, Hydration, Thermal expansion of salt

Salt weathering can cause substantial deterioration of natural rocks, building stones, masonry materials, monuments, andengineering structures. Nearly two centuries of salt weatheringstudies, both theoretically and empirically, have manifested its
power as well as its complexity. This paper attempts to unite thekinds of literature assess the various theories in the light of the
combined information. The theoretical approaches concerning
the most cited mechanisms of salt weathering such as crystallization, hydration and thermal expansion of crystalline salts arethoroughly reviewed. It is understood that there is no universally
acceptable hard and sound theoretical information on this topic
yet. More precise theories should be developed to elucidate thecomplications of the mechanisms of salt weathering as well as
to interpret the results of empirical studies.

Example of a honeycomb structure at Giza, Egypt.

Published: 2021/5/7
https://doi.org/10.1186/s40645-021-00414-x― 51 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Human geosciences

Arsenic cycling in the Earth’s crust and hydrosphere: interaction between naturally occurring
arsenic and human activities
Masuda H[Keywords] Arsenic contamination, geologic cycle, plate tectonics, reduction, oxidation

Field-based research on naturally occurring
arsenic contamination of surface waters andgroundwaters and the mechanisms of contamination are reviewed. The distribution of arsenic
is strongly related to areas of active plate tectonics, magmatism and associated hydrothermal activity, and high rates of erosion. Sourcesof arsenic contamination are mainly hydrothermal water, sulfide and arsenide minerals, volcanic ash, and iron oxyhydroxide/oxide as weathering products. The promotion of the reduction
and oxidation of arsenic source minerals by insitu microbial activity is an important secondary
mechanism that often determines arsenic levels
in groundwater. Anthropogenic activities, suchas geothermal and mining operations, as well

Geologic cycle concerning arsenic transportation in the geosphere andsurface of the Earth shows the arsenic recycles in association with active
tectonics.
Digit in parenthesis gives the average concentrations of each geologic

as excess pumping of shallow groundwaters,

bpdy. Purple and blue colored letters indicate the releasing and fixing

disperse arsenic in the environment, thereby

mechanisms of arsenic in the cycle.

expanding areas of arsenic contamination.

Published: 2018/11/1
https://doi.org/10.1186/s40645-018-0224-3― 52 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Biogeosciences

Liquid and supercritical CO2 as an organic solvent in Hadean seafloor hydrothermal systems:
implications for prebiotic chemical evolution
Takazo Shibuya, Ken Takai[Keywords] Origin of life, Liquid and supercritical CO2, CO2 hydrate, Seafloor hydrothermal vent, Prebiotic chemical
evolution, Phase separation, Organic solvent, Interface reaction, Metal dissolution

Prebiotic chemical evolution and the emergence oflife in the seafloor hydrothermal systems of Hadean
Earth is among the most plausible and popular hypotheses for the origin of earthly life. In contrast, manystudies pointed out that this hypothesis intrinsicallyharbors a critical unsolved problem called the “waterparadox”: Abundant water limits dehydration synthesis and instead facilitates hydrolysis of organic molecules during the early stage of chemical evolution.
However, many of these criticisms have not referred tothe abundant liquid/supercritical CO2 (L/SC-CO2) fluids and pools in modern hydrothermal systems, which
not only create dry environments but also behave ashydrophobic solvents at and beneath the seafloor. In
this paper, we theorize the generation and preservationof a L/SC-CO2 pool in modern seafloor hydrothermal
systems and reinterpret the fossil hydrothermal systems preserved in early Archean seafloor basalts. The
theoretical estimation of subseafloor phase separationand phase segregation of CO2-rich hydrothermal fluids
suggests the presence of L/SC-CO2 fluids and pools in
Hadean seafloor hydrothermal systems. Because they
behave as hydrophobic organic solvents, L/SC-CO2 canpotentially initiate the dehydration synthesis of organic
molecules in seafloor hydrothermal systems. Moreover,at the interface between L/SC-CO2 and H2O-rich fluid(seawater or hydrothermal fluid), amphiphilic molecules
might be generated and triggered into self-assembled
growth. Based on the abundant occurrence and physicochemical properties of L/SC-CO2 fluids, we propose
a new stepwise concept for the origin of life, whereby
prebiotic chemical evolution was co-hosted and facilitated by L/SC-CO2 in Hadean water-rich seafloorhydrothermal systems. This “liquid/supercritical CO2
hypothesis” potentially overcomes the water paradox
and strengthens the idea that earthly life was hatchedin deep-sea hydrothermal systems.

Schematic of Hadean seafloor hydrothermal systems bearing aliquid/supercritical CO2 (L/SC-CO2) pool. The CO2-rich seawater
infiltrates the subseafloor volcanic rocks and reacts with basalts
or komatiites, causing carbonation and alteration of basalts or serpentinization of komatiites in the seawater recharge zones. Whenhydrothermal fluid reaches the reaction zone, it receives abundantdegassed CO2 from an underlying magmatic heat source. During
fluid upwelling, phase separation of the CO2-rich hydrothermal fluid
progressively occurs through depressurization, which likely condenses the CO2 in the vapor phase. If the CO2-rich vapor phaseis physically segregated from the main flow channel of the upwelling brine phase, it is continuously mixed with recharged seawater
and/or cooler pore fluid, causing further phase separation by thetemperature decrease. CO2 is then purified in vapor phase. Eventually, these condensation and purification processes generate many
SC-CO2 droplets beneath the seafloor. The SC-CO2 is less dense
than seawater and migrates upward. As it cools during the upwardmigration, its phase converts to L-CO2. These processes form alarge L/SC-CO2 pool beneath the seafloor. If the temperature of
the bottom seawater is lower than approximately 10 °C, reactions
between L-CO2 and the ambient seawater/pore fluid requisitely
generate solid CO2 hydrates that cement the pores, voids andcavities of the hydrothermal sediments and permeable volcanics.
This self-sealing effect by CO2 hydrates prevents the leakage of L/
SC-CO2 through the seafloor. In contrast, when CO2 hydrates areabsent in the vicinity of warm/hot hydrothermal vents, L/SC-CO2
leaks from the inner edge of the pool and enters the upwelling hydrothermal fluid just below the seafloor, where it is emitted in the formof bubbles. L-CO2 containing these bubbles transforms to hydratecoated L-CO2 during upward migration through the water column.
The bubbles disappear at depths around 500 m because L-CO2 andCO2 hydrate are unstable at these depths. Eventually, both CO2 gas
and the organic molecules dissolved in L/SC-CO2 are released tothe ambient seawater. If the hydrothermal vents are black-smoker
type, the L-CO2 bubbles will carry heavy metals upward to the shallower part of the water column.

Published: 2022/11/15
https://doi.org/10.1186/s40645-022-00510-6― 53 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Biogeosciences

Perspective on the response of marine calcifiers to global warming and ocean acidification –Behavior of corals and foraminifera in a high CO2 world “hot house”
Kawahata H, Fujita K, Iguchi A, Inoue M, Iwasaki S, Kuroyamagi A, Maeda A, Manaka T, Moriya K, Takagi H,
Toyofuku T, Yoshimura T, Suzuki A[Keywords] Partial pressure of CO2, Global warming, Ocean acidification, Coral, Foraminifera, Bleaching, Calcite,
Aragonite, Saturation state, Organic matter, Alkalinity, Carbon cycle

The CO2 concentration of air has increased over the last two
centuries and recently surpassed 400 ppm. Carbon cycle models project CO2 concentrations of 720 to 1000 ppm for the IPCC
intermediate scenario (RCP 6.0), resulting in an increase in global
mean temperature of ~2.6 °C and a decrease in seawater pH of~0.3. Together, global warming and ocean acidification are often
referred to as the “evil twins” of climate change, potentially inducing severe threats in the near future. In this paper, our discussion
is focused on the response of two major calcifiers, foraminifera
and corals, which contribute much to the global carbonate burial
rate. Photosymbiosis is regarded as an adaptive ecology for living in warm and oligotrophic oceans, especially for reef-building
corals and larger reef-dwelling benthic foraminifera. As a consequence of global warming, bleaching may be a global threat toalgal symbiont-bearing marine calcifying organisms under conditions of high temperature and light intensity. If CO2 is dissolved
in seawater, the partial pressure of CO2 in seawater (pCO2) anddissolved inorganic carbon (DIC) increases while pH and the saturation state of carbonate minerals decreases without any change
Fig. 1. Comparison of an acidification condition experin total alkalinity. Generally, marine calcifying organisms show
iment and the growth weight of foraminifera.
decreases in calcification rates in response to acidified seawaFig. 2. Schematic diagram of ocean acidification andter. However, the response often differs depending on situations,the buffering system in the Earth’s surface system.
species, and life-cycle stage. Some benthic foraminifera showed
a positive response to low pH conditions. The Acropora digitifera
coral calcification of adult branches was not reduced markedly at higher pCO2 conditions, although calcification tended
to decrease versus pCO2 in both aposymbiotic and symbiotic polyps. New analytical technologies help identify important constraints on calcification processes. Based upon Ca isotopes, the transport path of Ca2+ and the degree of its
activity would predominantly control the carbonate precipitation rate. Visualization of the extracellular pH distribution
shows that proton pumping produces the high internal pH and large internal–external pH gap in association with foraminiferal calcification. From the perspective of a long-term change in the Earth’s surface environment, foraminifera
seem to be more adaptive and robust than corals in coping with ocean warming and acidification but it is necessary
to further understand the mechanisms underlying variations in sensitivity to heat stress and acidified seawater for
future prediction. Since CO2 is more soluble in lower temperature seawater, ocean acidification is more critical in thepolar and high-latitude regions. Additionally, older deep-water has enhanced acidity owing to the addition of CO2 fromthe degradation of organic matter via a synergistic effect with high pressure. With current ocean acidification, pH
and the saturation state of carbonate minerals are decreasing without any change in total alkalinity. However, in the
Earth’s history, it is well known that alkalinity has fluctuated significantly. Therefore, it is necessary to quantitatively
reconstruct alkalinity, which is another key factor determining the saturation state of carbonate minerals. The rapid
release of anthropogenic CO2 (in the present day and at the Paleocene/Eocene boundary) induces severe ocean
acidification, whereas in the Cretaceous, slow environmental change, even at high levels of pCO2, could raisealkalinity, thereby neutralizing ocean acidification.
Published: 2019/1/17
https://doi.org/10.1186/s40645-018-0239-9― 54 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Biogeosciences

Theoretical constraints of physical and chemical properties of hydrothermal fluids on variations
in chemolithotrophic microbial communities in seafloor hydrothermal systems.
Nakamura K, Takai K[Keywords] Deep-sea hydrothermal systems, Chemosynthetic ecosystems, Hydrothermal fluid chemistry, Host rockgeochemistry, Geochemical modeling, Bioavailable energy yieldIn the past few decades, chemosynthetic
ecosystems at deep-sea hydrothermal vents
have received attention as plausible analogues
to the early ecosystems of Earth, as well as toextraterrestrial ecosystems. These ecosystems
are sustained by chemical energy obtained frominorganic redox substances (e.g., H2S, CO2, H2,
CH4, and O2) in hydrothermal fluids and ambient seawater. The chemical and isotope compositions of the hydrothermal fluid are, in turn,controlled by subseafloor physical and chemical processes, including fluid–rock interactions,
phase separation and partitioning of fluids, andMetabolic energies available from each (Left) aerobic and (Right) anaero-precipitation of minerals. We hypothesized thatbic reactions for chemolithoautotrophy considered in this study

specific physicochemical principles describe thelinkages among the living ecosystems, hydrothermal fluids, and geological background in deep-sea hydrothermal
systems. We estimated the metabolic energy potentially available for productivity by chemolithotrophic microorganisms at various hydrothermal vent fields. We used a geochemical model based on hydrothermal fluid chemistry datacompiled from 89 globally distributed hydrothermal vent sites. The model estimates were compared to the observed
variability in extant microbial communities in seafloor hydrothermal environments. Our calculations clearly show that
representative chemolithotrophic metabolisms (e.g., thiotrophic, hydrogenotrophic, and methanotrophic) respond differently to geological and geochemical variations in the hydrothermal systems. Nearly all of the deep-sea hydrothermal
systems provide abundant energy for organisms with aerobic thiotrophic metabolisms; observed variations in the
H2S concentrations among the hydrothermal fluids had little effect on the energetics of thiotrophic metabolism. Thus,
these organisms form the base of the chemosynthetic microbial community in global deep-sea hydrothermal environments. In contrast, variations in H2 concentrations in hydrothermal fluids significantly impact organisms with aerobic
and anaerobic hydrogenotrophic metabolisms. Particularly in H2-rich ultramafic rock-hosted hydrothermal systems,
anaerobic and aerobic hydrogenotrophy is more energetically significant than thiotrophy. The CH4 concentration also
has a considerable impact on organisms with aerobic and anaerobic methanotrophic metabolisms, particularly in sediment-associated hydrothermal systems. Recently clarified patterns and functions of existing microbial communities
and their metabolisms are generally consistent with the results of our thermodynamic modeling of the hydrothermal
mixing zones. These relationships provide important directions for future research addressing the origin and early
evolution of life on Earth as well as for the search for extraterrestrial life.

Published: 2014/4/22
https://doi.org/10.1186/2197-4284-1-5― 55 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Biogeosciences

Biochemical and physiological bases for the use of carbon and nitrogen isotopes in environmental and ecological studies
Ohkouchi N, Ogawa N O, Chikaraishi Y, Tanaka H, Wada E[Keywords] Carbon isotopic composition, Nitrogen isotopic composition, Ecosystem, Food web, Chlorophyll, Trophic
position, Amino acid, Animal organ

We review the biochemical and physiologicalbases of the use of carbon and nitrogen isotopic
compositions as an approach for environmental and ecological studies. Biochemical processes commonly observed in the biosphere,
including the decarboxylation and deaminationof amino acids, are the key factors in this isotopic approach. The principles drawn from theisotopic distributions disentangle the complex
dynamics of the biosphere and allow the interactions between the geosphere and biosphereto be analyzed in detail. We also summarize two
recently examined topics with new datasets: theisotopic compositions of individual biosynthetic
products (chlorophylls and amino acids) andthose of animal organs for further pursuing thebasis of the methodology. As a tool for investigating complex systems, compound-specificisotopic analysis compensates the intrinsic disadvantages of bulk isotopic signatures. Chlorophylls provide information about the particular
processes of various photoautotrophs, whereas
amino acids provide a precise measure of theTrophic positions of organisms from Lake Baikal based on the nitrogen

trophic positions of heterotrophs. The isotopic

isotopic composition of amino acids (glutamic acid and phenylalanine).

distributions of carbon and nitrogen in a single“TP” denotes trophic position.

organism as well as in the whole biosphere arestrongly regulated, so that their major components such as amino acids are coordinated appropriately rather thancontrolled separately.

Published: 2014/2/3
https://doi.org/10.1186/s40645-015-0032-y― 56 ―

Review
Solid earth sciences

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Significance of the high-pressure properties and structural evolution of gas hydrates for inferring
the interior of icy bodies
Hisako Hirai, Hirokazu Kadobayashi[Keywords] Methane hydrate, Hydrogen hydrate, High-pressure properties, High and low temperatures, Structural
evolution, Transition mechanism, Guest orientational ordering, Molecular dissociation, Icy bodies, Diamond-anvil cell
(DAC)

Hydrogen, methane, and water ice are among
the most abundant materials in the universe.
Based on experimental, theoretical, and spacecraft data, gas hydrates consisting of gas andwater ice have been predicted to exist throughout the universe. This review discusses thehigh-pressure properties of two common gas
hydrates (methane and hydrogen hydrates) at
low and high temperatures based primarily on
experimental results. Gas hydrates consist of awater molecule host and a gaseous guest. They
have a clathrate structure at low pressure anda filled-ice structure at high pressure. The hostencloses the guest, and a specific interaction
occurs between the guest and host, resulting in
unique physical properties. When subjected to

An overview of the structural evolution of (top) MH and (bottom) HH afterpressure, gas hydrates undergo various phasetransition to the filled-ice structure, except for HH-C0. With increasingchanges. Based on pressure and guest size,pressure, the guests undergo stepwise orientational ordering accompanieda general rule for phase changes occurring inby structural changes. Hydrogen-bond symmetrization of the host was

gas hydrates exists. Analysis of the phase-tran-

predicted to occurs at even higher pressures.

sition mechanism shows that some cages aremaintained after the transition to the next clathrate structure, while others are recombined into different cages of thenext structure. This is a novel mechanism that can be called “cage recombination mechanism.” Low-temperature andhigh-pressure experiments have revealed that as the pressure increases, the guest molecules undergo a stepwise
progression of orientational ordering, i.e., restriction of free rotation, which induces structural changes that stabilize thestructure at high pressure. Theoretical studies have predicted that hydrogen-bond symmetrization in the host occurs
at even higher pressures, further stabilizing the structure. Thus, hydrates respond to environmental changes such aspressure to achieve self-organization by the orientational ordering of the guest and hydrogen-bond symmetrization of
the host. Additionally, results of high-temperature and high-pressure experiments conducted at conditions comparable
to those in Neptune’s ice mantle show that methane hydrate decomposes into solid methane and ice VII, both ofwhich melt at further elevated temperatures. Then, the methane molecules undergo further molecular dissociation toform diamonds. These findings are valuable for modeling the interiors of icy planets and understanding how magnetic
fields and heat are generated.

Published: 2023/1/13
https://doi.org/10.1186/s40645-023-00534-6― 58 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

A review on slow earthquakes in the Japan TrenchTomoaki Nishikawa, Satoshi Ide, Takuya Nishimura[Keywords] Japan Trench ,Slow earthquake, Tectonic tremor, Very-low-frequency earthquake, Slow slip event,
Megathrust earthquake, Tohoku-Oki earthquake, Subduction zone, Crustal structure, Geological environment

Slow earthquakes are episodic slow fault
slips. They form a fundamental component ofinterplate deformation processes, along with
fast, regular earthquakes. Recent seismological and geodetic observations have revealed
detailed slow earthquake activity along theJapan Trench—the subduction zone where
the March 11, 2011, moment magnitude (Mw)
9.0 Tohoku-Oki earthquake occurred. In thispaper, we review observational, experimental,
and simulation studies on slow earthquakes
along the Japan Trench and their researchhistory. By compiling the observations of slow
earthquakes (e.g., tectonic tremors, very-lowfrequency earthquakes, and slow slip events)
and related fault slip phenomena (e.g., small
repeating earthquakes, earthquake swarms,
and foreshocks of large interplate earthquakes),
we present an integrated slow earthquake distribution along the Japan Trench. Slow andmegathrust earthquakes are spatially complementary in distribution, and slow earthquakes

Distribution of slow and fast (regular) earthquakes in the Japan Trenchand Nankai Trough. Blue and red symbols indicate areas where slow andfast earthquakes occur, respectively.

sometimes trigger fast earthquakes in theirvicinities. An approximately 200-km-long alongstrike gap of seismic slow earthquakes (i.e., tectonic tremors and very-low-frequency earthquakes) corresponds withthe huge interplate locked zone of the central Japan Trench. The Mw 9.0 Tohoku-Oki earthquake ruptured this locked
zone, but the rupture terminated without propagating deep into the slow-earthquake-genic regions in the northern andsouthern Japan Trench. Slow earthquakes are involved in both the rupture initiation and termination processes ofmegathrust earthquakes in the Japan Trench. We then compared the integrated slow earthquake distribution with thecrustal structure of the Japan Trench (e.g., interplate sedimentary units, subducting seamounts, petit-spot volcanoes,
horst and graben structures, residual gravity, seismic velocity structure, and plate boundary reflection intensity) anddescribed the geological environment of the slow-earthquake-genic regions (e.g., water sources, pressure–temperature conditions, and metamorphism). The integrated slow earthquake distribution enabled us to comprehensively
discuss the role of slow earthquakes in the occurrence process of the Tohoku-Oki earthquake. The correspondencesof the slow earthquake distribution with the crustal structure and geological environment provide insights into theslow-earthquake-genesis in the Japan Trench and imply that highly overpressured fluids are key to understanding thecomplex slow earthquake distribution. Furthermore, we propose that detailed monitoring of slow earthquake activity
can improve the forecasts of interplate seismicity along the Japan Trench.
Published: 2023/1/3
https://doi.org/10.1186/s40645-022-00528-w― 59 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

The role of hydrogen bonds in hydrous minerals stable at lower mantle pressure conditions
Jun Tsuchiya, Elizabeth C. Thompson[Keywords] Hydrous minerals, Ab initio calculation, Hydrogen bond, High pressure, Lower mantle

Over the past few decades, hydrous minerals were
thought to be absent in the lower mantle, due to theirinstability at high-pressure conditions. Recently, however,hydrous phases including phase H (MgSiO4H2), pyrite-type
FeOOH, and δ-AlOOH have been discovered to be thermodynamically stable at lower mantle pressures. Investigations using ab initio calculations methods play a keyrole in identifying these novel phases and determining
their geophysical properties (i.e., compressibility, elasticity,and sound velocities). These calculations suggest that thehydrous minerals which are stable at lower mantle pressure conditions (i.e., phase H, FeOOH, and AlOOH), havesymmetric hydrogen bonds at these pressures. This indicates that hydrogen bond strength is closely connected tothe stability and physical properties of hydrous minerals
at extreme pressures. In this review, we summarize thetheoretical and experimental studies of hydrous minerals
stable at the high-pressure conditions of the Earth’s lower
mantle in light of the role of hydrogen bonding.

The relationship between O...O and O-H distances (upper
panel), and O...O distance and O-H...O angle (lower panel) of
InOOH, AlOOH, FeOOH and DHMSs. It has been shown that
there is a clear difference in compressive behavior betweenhydrous minerals that undergo hydrogen bond symmetrizationand those that do not undergo symmetrization. In minerals
without hydrogen bond symmetrization, the hydrogen bonds
remain asymmetric even under extreme high-pressure
conditions (e.g., 100 GPa).

Published: 2022/11/17
https://doi.org/10.1186/s40645-022-00521-3― 60 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Fluids and physicochemical properties and processes in the Earth
Bjorn Mysen[Keywords] Fluid, Solubility, Thermodynamics, Mass transport, Permeability, Porosity, Wetting angle

The Earth’s fluid budget is dominated by species in the system C–O–H–N–S together withhalogens such as F and Cl. H2O is by far themost abundant. Such fluids are one of the twomain mass transport agents (fluid and magma)
in the Earth. Among those, in particular aqueous fluids are efficient solvents of geochemically important components at high temperatureand pressure. The solution capacity of aqueous
fluids can be enhanced further by dissolved halogens and sulfur. CO2 or nitrogen species has
the opposite effect.
Fluid-mediated transport in the Earth is by fluids passing through cracks at shallow depth andvia percolation channels along grain boundaries
at greater depth. Percolation velocity is linked
to permeability, which, in turn is governed byrock porosity. Porosity is controlled by wetting angles, θ, at the interface between fluid and mineral surfaces. When
θ < 60°, fluid will wet all grain boundaries of an isotropic crystalline material, whereas when greater than 60°, grainboundary wetting does not occur as readily, and fluid-mediated transport efficiency can be greatly reduced. The sizeof the wetting angle is negatively correlated with the solubility of silicate components in the fluids, which means thatfluid composition, temperature, and pressure affect the wetting angles and, therefore, fluid-mediated mass transport
efficiency in the interior of the Earth.
Geophysical and geochemical anomalies in the Earth’s interior have been linked to the presence of fluids. Fluid
infiltration in crustal and mantle rocks will enhance electrical conductivity and seismic wave attenuation. For example,
5–10% H2O-rich fluids in the mantle wedge above subducting plates have been suggested from enhanced electricalconductivity. Similar fluid fractions have been suggested to be consistent with seismic velocities in these regions.
The geochemistry of the crust and the mantle can be affected by fluid-mediated transport of major, minor, and traceelements. When such altered materials serve as source rocks of partial melts, those geochemical alterations also
lead to changes in partial melt compositions. As an example, the presence of such aqueous fluid in the mantle wedge
above subducting and dehydrating subducting slabs is consistent with partial melting of an H2O-bearing mantle wedge
above subducted oceanic crust.

Published: 2022/10/5
https://doi.org/10.1186/s40645-022-00516-0― 61 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

DigitSeis: Software to Extract Time Series from Analogue Seismograms
Miaki Ishii, Hiromi Ishii[Keywords] analogue seismograms, digitization, DigitSeis software

A vast amount of analogue seismograms recorded
between the end of the nineteenth century and late twentiethcentury are often inaccessible for seismological research
since they are not available as digital time series. This manuscript describes freely available software, DigitSeis, thattakes a digital image of an analogue seismic record andreturns waveforms either as a function of their x-y positionon the image or as time–amplitude information. The overall
structure and approach of the software are provided alongwith how they have evolved over different versions. The

Fig.1 Screenshot of DigitSeis version 1.6β (with display ineffectiveness of the software is demonstrated with three

Japanese) showing the short-period vertical recording fromexamples. The first example is a long-period east–west

Tuczon, Arizona between July 15 and 16, 1945. Digitized

seismogram recorded at the Harvard Seismographic Obser-

traces in colour have been overlain on top of the scannedvatory on photographic paper in May of 1938, which con-seismogram image with yellow vertical bars indicating eachtains signals associated with a magnitude 7.7 earthquake

minute (each hour is also labelled in yellow). The largethat occurred off the coast of Northern Ibaraki, Japan. The

arrivals in white are those associated with the Trinity nuclear
test.

second example is an analysis of a 35-mm microfilm copyof the short-period vertical seismogram recorded at Tucson,
Arizona, on July 16, 1945, that shows blast signals fromthe first nuclear bomb detonation. The final example uses
a 70 mm microfiche image of a long-period north–south
seismogram recorded at College, Alaska in December of
1966, which shows a pair of earthquakes with nearly iden-

Fig.2 Part of long-period north-south motion recorded at COL

tical waveforms. The software is, by no means, perfect,

station (College, Alaska) on December 19, 1966.

and discussion of its limitations such as the compatibility(Left) The section of the scanned microfiche image.
(Right) Same image with digitized traces for two of the lines

with pen- and Develocorder-type seismograms is included,

shown in cyan and magenta.

as well as comments about challenges of incorporatingmachine learning into the digitization process.

Published: 2022/10/1
https://doi.org/10.1186/s40645-022-00508-0― 62 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Review of the Early–Middle Pleistocene boundary and Marine Isotope Stage 19
Martin J. Head
[Keywords] Early–Middle Pleistocene, Quaternary, GSSP, MIS 19, Chiba

The Global Boundary Stratotype Section and Point(GSSP) defining the base of the Chibanian Stage andMiddle Pleistocene Subseries at the Chiba section,
Japan, was ratified on January 17, 2020. Although thiscompleted a process initiated by the International Union
for Quaternary Research in 1973, the term Middle Pleistocene had been in use since the 1860s. The Chiba
GSSP occurs immediately below the top of Marine
Isotope Substage (MIS) 19c and has an astronomical
age of 774.1 ka. The Matuyama-Brunhes paleomagnetic reversal has a directional midpoint just 1.1 m
above the GSSP and serves as the primary guide to
the boundary. This reversal lies within the Early-Middle
Pleistocene transition and has long been favoured tomark the base of the Middle Pleistocene. MIS 19 occurs
within an interval of low-amplitude orbital eccentricity
and was triggered by an obliquity cycle. It spans two
insolation peaks resulting from precession minima andhas a duration of ～ 28 to 33 kyr. MIS 19c begins ～791-787.5 ka, includes full interglacial conditions whichlasted for ～ 8-12.5 kyr, and ends with glacial inception
at ～ 774-777 ka. This inception has left an array of

The Quaternary System/Period and its official subdivision as
currently approved by the ICS and ratified by the IUGS EC. The
Upper Pleistocene Subseries has yet to be officially defined.
GSSP = Global Boundary Stratotype Section and Point.

climatostratigraphic signals close to the Early-Middle
Pleistocene boundary. MIS 19b-a contains a series of three or four interstadials often with rectangular-shaped waveforms and marked by abrupt (< 200 year) transitions. Intervening stadials including the inception of glaciation arelinked to the calving of ice sheets into the northern North Atlantic and consequent disruption of the Atlantic meridional
overturning circulation (AMOC), which by means of the thermal bipolar seesaw caused phase-lagged warming eventsin the Antarctic. The coherence of stadial-interstadial oscillations during MIS 19b-a across the Asian-Pacific and North
Atlantic-Mediterranean realms suggests AMOC-originated shifts in the Intertropical Convergence Zone and pacing by
equatorial insolation forcing. Low-latitude monsoon dynamics appear to have amplified responses regionally although
high-latitude teleconnections may also have played a role.

Published: 2021/9/3
https://doi.org/10.1186/s40645-021-00439-2― 63 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Visualizing heterogeneities of earthquake hypocenter catalogs: modeling, analysis, and compensation
Ogata Y
[Keywords] ABIC, Bias compensation, Detection rate function, Empirical Bayesian method, Data heterogeneity,
Hypocenter catalogs, Location corrections, MAP solutions, Magnitude-shift, Smoothness constraints

As basic data for seismic activity analysis,
hypocenter catalogs need to be accurate, complete, homogeneous, and consistent. Therefore, clarifying systematic errors in catalogs is
an important discipline of seismicity research.
This review presents a systematic model-based
methodology to reveal various biases and theresults of the following analyses. (1) It is criticalto examine whether there is a non-stationary
systematic estimation bias in earthquake magnitudes in a hypocenter catalog. (2) Most earthquake catalogs covering long periods are nothomogeneous in space, time, and magnitude
ranges. Earthquake network structures andseismometers change over time, and therefore, earthquake detection rates change overtime and space. Even in the short term, many
aftershocks immediately following large earthquakes are often undetected, and the detection rate varies, dependingon the elapsed time and location. By establishing a detection rate function, the actual seismic activity and the spatiotemporal heterogeneity of catalogs can be discriminated. (3) Near real-time correction of source locations, far from theseismic observation network, can be implemented based on better determined source location comparisons of othercatalogs using the same identified earthquakes. The bias functions were estimated using an empirical Bayes method.
I provide examples showing different conclusions about the changes in seismicity from different earthquake catalogs.
Through these analyses, I also present actual examples of successful modifications as well as various misleading
conclusions about changes in seismic activity. In particular, there is a human made magnitude shift problem includedin the global catalog of large earthquakes in the late nineteenth and early twentieth centuries.

Published: 2021/1/21
https://doi.org/10.1186/s40645-020-00401-8― 64 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Strength models of the terrestrial planets and implications for their lithospheric structure andevolution
Ikuo Katayama[Keywords] Rheological structure, Lithosphere, Elastic thickness, Terrestrial planets

Knowledge of lithospheric strength can help
to understand the internal structure and evolution of the terrestrial planets, as surface topography and gravity fields are controlled mainly
by deformational features within the lithosphere.
Here, strength profiles of lithosphere were calculated for each planet using a recently updated
flow law and taking into account the effect ofwater on lithospheric deformation. Strength isStrength models of terrestrial planets calculated under dry (red lines) andcontrolled predominantly by brittle deformation

wet (blue lines) conditions.

at shallow depths, whereas plastic deformation
becomes dominant at greater depths through its sensitivity to temperature. Incorporation of Peierls creep, in which
strain rate is exponentially dependent on stress, results in the weakening of plastic strength at higher stress levels,and the transition from brittle to ductile deformation shifts to shallower depths than those calculated using conventional
power-law creep. Strength in both the brittle and ductile regimes is highly sensitive to the presence of water, with theoverall strength of the lithosphere decreasing markedly under wet conditions. The markedly low frictional coefficientof clay minerals results in a further decrease in brittle strength and is attributed to expansion of the brittle field. As
plastic strength is influenced by lithology, a large strength contrast can occur across the crust–mantle boundary if
deformation is controlled by ductile deformation. Effective elastic thickness for the terrestrial planets calculated fromthe rheological models indicates its close dependence on spatiotemporal variations in temperature and the presence ofwater. Although application of the strength models to observed large-scale surface deformational features is subject tolarge extrapolation and uncertainties, I emphasize the different sensitivity of these features to temperature and water,
meaning that quantifying these features (e.g., by data from orbiting satellites or rovers) should help to constrain theinternal structure and evolution of the terrestrial planets.

Published: 2021/1/4
https://doi.org/10.1186/s40645-020-00388-2― 65 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Deep mantle melting, global water circulation and its implications for the stability of the ocean
mass
Shun-ichiro Karato, Bijaya Karki, Jeffrey Park
[Keywords] habitability, ocean mass, sea-level variations, mantle transition zone, water in the mantle, deep mantle
melting, water valve

Oceans on Earth are present as a result ofdynamic equilibrium between degassing and regassing through the interaction with Earth’s interior. We
review mineral physics, geophysical, and geochemical studies related to the global water circulation andconclude that the water content has a peak in the
mantle transition zone (MTZ) with a value of 0.1–1
wt% (with large regional variations). When water-rich
MTZ materials are transported out of the MTZ, partial melting occurs. Vertical direction of melt migration is determined by the density contrast between

Processes of water transport across the 410-km with heterogeneous

the melts and coexisting minerals. Because a den-temperaturesity change associated with a phase transformation
occurs sharply for a solid but more gradually for amelt, melts formed above the phase transformation
depth are generally heavier than solids, whereas
melts formed below the transformation depth arelighter than solids. Consequently, hydrous melts
formed either above or below the MTZ return to the
MTZ, maintaining its high water content. However,the MTZ water content cannot increase without
limit. The melt-solid density contrast above the 410
km depends on the temperature. In cooler regions,
melting will occur only in the presence of very waterrich materials. Melts produced in these regions havehigh water content and hence can be buoyant above
the 410 km, removing water from the MTZ. Consequently, cooler regions of melting act as a water
valve to maintain the water content of the MTZ nearits threshold level (~0.1–1.0 wt%). Mass-balance
considerations explain the observed near-constant

Results of model calculations on ocean mass history

sea-level despite large fluctuations over Earth history. Observations suggesting deep-mantle melting are reviewed
including the presence of low-velocity anomalies just above and below the MTZ and geochemical evidence for hydrous
melts formed in the MTZ. However, the interpretation of long-term sea-level change and the role of deep mantle melting in the global water circulation are non-unique and alternative models are reviewed. Possible future directions ofstudies on the global water circulation are proposed including geodynamic modeling, mineral physics and observational
studies, and studies integrating results from different disciplines.
Published: 2020/12/10
https://doi.org/10.1186/s40645-020-00379-3― 66 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

A coupled core-mantle evolution: Review and future prospects
Takashi Nakagawa[Keywords] Geomagnetic field, Earth’s core, Deep mantle, Long-term evolution

In this review, I provide the current status andfuture prospects for the coupled core-mantle
evolution and specifically summarize the constraints arising from geomagnetism and paleomagnetism on the long-term secular variationsof the geomagnetic field. The heat flow acrossthe core-mantle boundary (CMB) is essential for
determining the best-fit scenario that explains
the observational data of geomagnetic secularvariations (e.g., onset timing of the inner core
growth, geomagnetic polarity reversals, andwestward drift) and should include the various
origins of the heterogeneous structures in the
deep mantle that have affected the heat transfer across the core-mantle boundary for billionsof years. The coupled core-mantle evolution
model can potentially explain the onset timingof the inner core and its influence on the longterm geomagnetic secular variations, but it isstill controversial among modeling approaches
on the core energetics because the paleomagnetic data contains various uncertainties. Additionally, with the coupled core-mantle evolution
model in geodynamo simulations, the frequencyof the geomagnetic polarity reversals can be(a) Schematic illustration of the coupled core-mantle evolution system;

explained with the time variations of the heat(b) Zoom-up of the thermal structure across the core-mantle boundary;flow across the CMB. Additionally, the effects(c) Schematic illustration of the feedback mechanism between core andof the stable region in the outermost outer coreto the magnetic evolution are also crucial but

mantle evolution; (d) An example result on the coupled core-mantle evolution model in parameterized mantle convection computation (Upper left:
Thermal structure of the mantle; Upper right; Heat budget in the man-

there would be still uncertain for their feasibility.

tle; Lower left: Size of the inner core as a function of time; Lower right:

However, despite this progress in under-

Magnetic moment). On the magnetic moment, two values of the thermal

standing the observational data for geomag-

conductivity of the Earth’s core are assumed (163 W/m/K and 125 W/m/K).

netic secular variations, there are several unresolved issues that should be addressed in future investigations: (1) initial conditions—starting with the solidification of
the global magma ocean with the onset timing of plate tectonics and geodynamo actions and (2) planetary habitability—how the dynamics of the Earth’s deep interior affects the long-term surface environment change that has been
maintained in the Earth’s multisphere coupled system.

Published: 2020/10/6
https://doi.org/10.1186/s40645-020-00374-8― 67 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Some remarks on hydrogen-assisted electrical conductivity in olivine and other minerals
Shun-ichiro Karato[Keywords] Electrical conductivity, Hydrogen, Water in the mantle, Point defects

Electrical conductivity in minerals is sensitive tohydrogen content, and therefore, it is a potentially
important property from which one can infer hydrogen (water) distribution in the mantle. However,there has been much confusion in the reported
results on hydrogen-assisted conductivity. In thispaper, I review the existing experimental observations on hydrogen-enhanced electrical conductivity in olivine and other minerals to identify thecauses of confusion. Hydrogen loss as well ashydrogen gain could occur during a conductivity
measurement at high pressures and temperatures. Particularly important is the unrecognizedhydrogen gain during an experiment that could
lead to a large degree of error. Many experiments

Electrical conductivity of hydrogen-bearing olivine. There is a system-

were conducted under the conditions where speci-

atic difference between low temperature and high temperature data.

mens were super-saturated with hydrogen making

High temperature data are consistent with geophysically inferred elec-

the validity of those results unclear. A model fortrical conductivity in the asthenosphere.

hydrogen loss is developed showing a strategy bywhich hydrogen loss can be minimized.
When one selects the experimental results in which the influence of hydrogen loss/gain are carefully examined,
there is no major discrepancy among the results from different laboratories except differences between the resultsfrom low and high temperatures. Differences between low-temperature and high-temperature results are caused by thechange in conduction mechanism. At low temperatures, conduction is due to the migration of interstitial (“free”) proton
and is nearly isotropic, whereas conduction at high temperatures is due to the migration of two protons at M-site thatis highly anisotropic. There is no evidence for substantial concentration dependence of activation enthalpy. Observed
exceptionally large concentration dependence reported by Poe et al. (Phys Earth Planet Inter 181:103-111, 2010) is
inconsistent with all other reports and is likely caused by some experimental artifact.
Experimental results in the high-temperature regime explain a majority of geophysical observations on the conductivity of the oceanic asthenosphere: partial melting is not needed in most regions and is rather inconsistent with theobservations on the matured oceanic mantle. Exception is the asthenosphere near the ridge and/or near the trench
where very high conductivity (~0.1 S/m) is reported at the top of the asthenosphere. Partial melting might play somerole in these regions.
Electrical conductivity in the continental lithosphere cannot be attributed entirely to olivine. An important role oforthopyroxene and/or other minor materials (graphite, sulfide) is needed to explain high conductivity reported in someregions such as Bushveld in South Africa.
The largest remaining uncertainty is the degree to which hydrogen affects electrical conductivity in the lower mantle
minerals. Determining the influence of hydrogen on electrical conductivity in lower mantle minerals is critical to makeprogress in understanding the global water circulation.
Published: 2019/8/12
https://doi.org/10.1186/s40645-019-0301-2― 68 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Detection of repeating earthquakes and their application in characterizing slow fault slip
Naoki Uchida[Keywords] Repeating earthquake, Interplate slip, Fault creep, Aseismic slip

Repeating earthquakes (repeaters) that
rupture the same fault area (patch) are interpreted to be caused by repeated accumulation
and release of stress on the seismic patch ina creeping area. This relationship between
repeaters with fault creep can be exploited for
tracking the fault creep (slow slip) based on therepeaters’ activity. In other words, the repeaters
can be used as creepmeters embedded on a
fault. To do this, it is fundamentally important toselect earthquakes that definitely re-rupture in
the same area. The selections are usually done
based on waveform similarity or hypocenter
location. In hypocenter-location based detec-

Estimation of interplate coupling based on repeating earthquake data (b)tion, the precision of the relative location com-and GPS data (a) (after Nomura et al., 2017).

pared with the dimension of earthquake sources
is critical for confirming the co-location of the source area. On the other hand, waveform-similarity-based detectionneeds to use appropriate parameters including high enough frequency components to distinguish neighboring sources.
Inter-event timing (recurrence interval) and/or the duration of a sequence’s activity are good diagnostic features forfinding appropriate detection parameters and eliminating non-repeating events, which are important because an inappropriate selection leads to including triggered sequences that do not re-rupture the same area. Repeaters provide an
independent estimation of creep from geodetic data and such estimations are mostly in good agreement when bothkinds of data are available. Repeater data are especially useful in the deeper part of strike-slip faults and in near-trench
areas of subduction zones where geodetic data’s resolution is usually limited. The repeaters also have an advantage
with geodetic data analysis because they are not contaminated by viscoelastic deformation or poroelastic reboundwhich are prominent postseismic process for large earthquakes and occur outside of faults. On the other hand, thedisadvantages of repeater analysis include their uneven spatial distribution and the uncertainty of the estimates of slip
amount requiring a scaling relationship between earthquake size and slip. There are considerable variations in theinferred slip amounts from different relationships. Applications of repeater analysis illuminate the spatial distribution ofinterplate stable slip, after slip, and spontaneous and cyclic slow slip events that represent important components ofinterplate slip processes in addition to major earthquakes.

Published: 2019/5/29
https://doi.org/10.1186/s40645-019-0284-z― 69 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Nitrogen in the Earth: abundance and transport
Bjorn Mysen[Keywords] Nitrogen, Recycling, Redox, Speciation, Solubility

The terrestrial nitrogen budget, distribution,and evolution are governed by biological andgeological recycling. The biological cycle provides the nitrogen input for the geological cycle,
which, in turn, feeds some of the nitrogen into
the Earth’s interior. A portion of the nitrogenalso is released back to the oceans and theatmosphere via N2 degassing. Nitrogen in silicate minerals (clay minerals, mica, feldspar,
garnet, wadsleyite, and bridgmanite) exists
predominantly as NH4+. Nitrogen also is foundin graphite and diamond where it occurs in elemental form. Nitrides are stable under extremely reducing conditions
such as those that existed during early planetary formation processes and may still persist in the lower mantle. Fromexperimentally determined nitrogen solubility in such materials, the silicate Earth is nitrogen undersaturated. The situation for the core is more uncertain, but reasonable Fe metal/silicate nitrogen partition coefficients (>10) would yield
nitrogen contents sufficient to account for the apparent nitrogen deficiency in the silicate Earth compared with othervolatiles. Transport of nitrogen takes place in silicate melt (magma), water-rich fluids, and as a minor component insilicate minerals. In melts, the N solubility is greater for reduced nitrogen, whereas the opposite appears to be thecase for N solubility in fluids. Reduced nitrogen species (NH3, NH2−, and NH2+) dominate in most environments of themodern Earth’s interior except the upper ~100 km of subduction zones where N2 is the most important species. Nitrogen in magmatic liquids in the early Earth probably was dominated by NH3 and NH2−, whereas in the modern Earth,
the less reduced, NH2+ functional group is more common. N2 is common in magmatic liquids in subduction zones.
Given the much lower solubility of N2 in magmatic liquids compared with other nitrogen species, nitrogen dissolved as
N2 in subduction zone magmas is expected to be recycled and returned to the oceans and the atmosphere, whereas
nitrogen in reduced form(s) likely would be transported to greater depths. This solubility difference, controlled primarily
by variations in redox conditions, may be a factor resulting in increased nitrogen in the Earth’s mantle and decreasing
abundance in its oceans and atmosphere during the Earth’s evolution. Such an abundance evolution has resulted in
the decoupling of nitrogen distribution in the solid Earth and the hydrosphere and atmosphere.

Published: 2019/5/20
https://doi.org/10.1186/s40645-019-0286-x― 70 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Earthquake Early Warning: what does “seconds before a strong hit” mean?
Tajima F, Hayashida T.
[Keywords] Earthquake early warning, effective preparation for seismic safety at recipients’ sites, short-wavelength
ground motion variation

An earthquake early warning (EEW) system is designed
to detect an event, determine its parameters (hypocenter,magnitude, and origin time), and issue an alert to sites/areas
where necessary actions should be taken before destructive
seismic energy arrivals. At present, large-scale EEW systems
are operational in several countries around the world. The
most extensive nationwide EEW system has been operatingin Japan since 2007, and was able to issue alerts broadly
when the moment magnitude (Mw) 9 Tohoku-Oki earthquake
hit in 2011. The casualties caused by this event were far lessthan those caused by other deadly earthquakes (Mw ≥ 6.6)in this century. Many other countries attributed the fewer
death victims to the advanced large-scale EEW system,and plan to install systems similar to Japan’s model. However, the historical and environmental background in Japan,
both in terms of earthquake hazards and safety preparation, differs considerably from other countries. In addition,
EEW systems that use data from a large-scale network (i.e.,“a big-net” hereafter) still have limitations. There are thus
numerous factors that other countries should consider tobenefit from installing a Japan-styled EEW. In this article,(top)

we review how research and development associated with

Big-net timeline of EEW alert issuance at tA and gray zones

EEW have been carried out, and how EEW systems pres-where strong shaking may arrive at tS before tA. The verticalently function. We then show short-wavelength variation ofaxis is the time relative to an earthquake origin time, andthe horizontal axis the epicentral distance (D). Gray zones

ground motions within the typical station interval of a big-net

are illustrated for networks of different station spacing Δx =using data recorded by a dense local seismic network in

10, 20, 30, and 40 km. For example, for a network of Δx =Japan. However, it is not particularly meaningful to attempt

20 km, the gray zone radius is ~17 km from the epicenter,detailed modeling of varieties of ground motion within thewhere the ground shaking may arrive before an alert andstation interval for a big-net EEW operation, because theis likely to be stronger, causing more damage than outside

possible combinations of earthquake sources, paths of wave

of it.

propagation, and recipient sites are infinite. We emphasize(bottom)that in all circumstances, for recipients to benefit from EEW,

Big-net station distributions: a. the station spacing in Japan

seismic safety preparations must be implemented. Neces-

average gray zone radius is ~17 km from a hypocenter;sary preparations at sites do not diminish in importance afterb. the station spacing in the West Coast/USA is not homo-incremental improvements in station coverage and/or algo-geneous, i.e., it is ~10 km in the populated metropolitan

rithms in a big-net operation. Further, scientists and engi-

areas such as around Los Angeles, San Francisco Bay andneers involved in EEW projects should strive to publically

Seattle whereas it is larger in less populated areas.

is ~20 km or less over the country. This implies that thedisseminate how big-net EEW systems work, and also why,to achieve maximum benefit, these systems should always
be supplemented by preparations at recipients’ sites.

Published: 2018/10/10
https://doi.org/10.1186/s40645-018-0221-6― 71 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Redox-controlled mechanisms of C and H isotope fractionation between silicate melt and COH
fluid in the Earth’s interior
Mysen B
[Keywords] Fluid, Solubility, Structure, Spectroscopy, Redox, Stable isotopes

The behavior of COH fluids, their isotopes(hydrogen and carbon), and their interaction with magmatic liquids are at the core ofunderstanding formation and evolution of the
Earth. Experimental data are needed to aid
our understanding of how COH volatiles affectrock-forming processes in the Earth’s interior.
Here, I present a review of experimental data on
structure of fluids and melts and an assessmentof how structural factors govern hydrogen andcarbon isotope partitioning within and between
melts and fluids as a function of redox conditions, temperature, and pressure.
The solubility of individual COH components
in silicate melts can differ by several ordersof magnitude and ranges from several hundred ppm to several wt%. Silicate solubility in
fluid can reach several molecular at mantle
temperatures and pressures. Different solubility of oxidized and reduced C-bearing species in melts reflects different solution equilibria. These equilibria are
2CH4+Qn=2CH3−+H2O+Qn+1 and 2CO32−+H2O+2Qn+1=HCO3−+2Qn, under reducing and oxidizing conditions, respectively. In the Qn-notations, the superscript, n, denotes the number of bridging oxygen in the silicate species (Q-species).
The structural changes of carbon and silicate in magmatic systems (melts and fluids) with variable redox conditions
result in hydrogen and carbon isotope fractionation factors between melt, fluid, and crystalline materials that dependon redox conditions and can differ significantly from 1 even at magmatic temperatures. The ΔH of D/H fractionation
between aqueous fluid and magma in silicate–COH systems is between −5 and 25 kJ/mol depending on redox conditions. The ΔH values for 13C/12C fractionation factors are near −3.2 and 1 kJ/mol under oxidizing and reducing conditions, respectively. These differences are because energetics of O–D, O–H, O–13C, and O–12C bonding environments
are governed by different solution mechanisms in melts and fluids.
From the above data, it is suggested that (COH)-saturated partial melts in the upper mantle can have δD values
100%, or more, lighter than coexisting silicate-saturated fluid. This effect is greater under oxidizing than under reducing
conditions. Analogous relationships exist for 13C/12C. At magmatic temperatures in the Earth’s upper mantle, 13C/12C
of melt in equilibrium with COH-bearing mantle in the −7 to −30‰ range increases with temperature from about 40
to >100‰ and 80–120‰ under oxidizing and reducing conditions, respectively.

Published: 2018/9/1
https://doi.org/10.1186/s40645-018-0203-8― 72 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Nonlinear dynamical analysis of GNSS data: quantification, precursors and synchronization
Hobbs B, Ord A[Keywords] GNSS time series, Nonlinear analysis, Dynamical systems, Recurrence plots, Recurrence quantification
analysis (RQA), Cross and joint recurrence plots, Crustal deformation, Precursors, Synchronisation

The goal of any nonlinear dynamical analysis of a data series is to extract features of the
dynamics of the underlying physical and chemical processes that produce that spatial patternor time series; a by-product is to characterise
the signal in terms of quantitative measures. In
this paper, we briefly review the methodology
involved in nonlinear analysis and explore timeseries for GNSS crustal displacements with aview to constraining the dynamics of the underlying tectonic processes responsible for the
kinematics. We use recurrence plots and theirquantification to extract the invariant measuresof the tectonic system including the embedding
dimension, the maximum Lyapunov exponent
and the entropy and characterise the systemusing recurrence quantification analysis (RQA).

Synchronisation of GNSS data in New Zealand. Colored map is a joint
recurrence plot of detrended coordinate time series (E-W component) at
CNST (below) and KAIK (left) sites. Correlation concentrates along the
diagonal line 250-400 days before large slow slip events (~800, =2100,
and 3300 days), indicating synchronisation.

These measures are used to develop a data
model for some GNSS data sets in New Zealand. The resulting dynamical model is tested using nonlinear prediction
algorithms. The behaviours of some RQA measures are shown to act as precursors to major jumps in crustal displacement rate. We explore synchronisation using cross- and joint-recurrence analyses between stations and showthat generalised synchronisation occurs between GNSS time series separated by up to 600 km. Synchronisation
between stations begins up to 250 to 400 days before a large displacement event and decreases immediately before
the event. The results are used to speculate on the coupled processes that may be responsible for the tectonics ofthe observed crustal deformations and that are compatible with the results of nonlinear analysis. The overall aim is toplace constraints on the nature of the global attractor that describes plate motions on the Earth.

Published: 2018/7/23
https://doi.org/10.1186/s40645-018-0193-6― 73 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California:
insight into mélange origins and subduction-accretion processes
John Wakabayashi[Keywords] Ocean plate stratigraphy, Subduction complex evolution, Subduction megathrust slip accommodation,
tectonic and sedimentary mélanges

The transfer (accretion) of materials from a
subducting oceanic plate to a subduction-accretionary complex has produced rock assemblages recording the history of the subductedoceanic plate from formation to arrival at the
trench. These rock assemblages, comprisingoceanic igneous rocks progressively overlain
by pelagic sedimentary rocks (chert and/or
limestone) and trench-fill clastic sedimentaryrocks (mostly sandstone, shale/mudstone),have been called ocean plate stratigraphy

Cross sectional cartoon showing accretion of OPS and the connection(OPS). During accretion of OPS, megathrust

between this process and the rock assemblages found in subduction com-

slip is accommodated by imbricate faults andplexes, including different types of mélanges. This schematic also illus-

penetrative strain, shortening the unit and lead-trates that olistostromes of serpentinite and/or siliciclastic matrix comprise

ing to tectonic repetition of the OPS sequence,part of the clastic part of OPS.

whereas OPS accreted at different times are
separated by non-accretionary megathrust horizons. The Franciscan subduction complex of California accreted episodically over a period of over 150 million years and incorporated OPS units with a variety of characteristics separated by non-accretionary megathrust horizons. Most Franciscan OPS comprises MORB (mid-ocean-ridge basalt)
progressively overlain by chert and trench-fill clastic sedimentary rocks that are composed of variable proportions ofturbidites and siliciclastic and serpentinite-matrix olistostromes (sedimentary mélanges). Volumetrically, the trenchfill component predominates in most Franciscan OPS, but some units have a significant component of igneous andpelagic rocks. Ocean island basalt (OIB) overlain by limestone is less common than MORB-chert assemblages, as
are abyssal serpentinized peridotite slabs. The earliest accreted OPS comprises metabasite of supra-subduction zone
affinity imbricated with smaller amounts of metaultramafic rocks and metachert, but lacking a clastic component. Most
deformation of Franciscan OPS is localized along discrete faults rather than being distributed in the form of penetrative
strain. This deformation locally results in block-in-matrix tectonic mélanges, in contrast to the sedimentary mélanges
making up part of the clastic OPS component. Such tectonic mélanges may include blocks and matrix derived from theolistostromes. Franciscan subduction and OPS accretion initiated in island arc crust at about 165–170 Ma, after which
MORB and OIB were subducted and accreted following a long (tens of mega-ampere) gap with little or no accretion.
Following subduction initiation, a ridge crest approached the trench but probably went dormant prior to its subduction(120–125 Ma), after which the subducted oceanic crust became progressively older until about 95 Ma. From 95 Ma,
the age of subducted oceanic crust decreased progressively until arrival of the Pacific-Farallon spreading center led
to termination of subduction and conversion to a transform plate boundary.

Published: 2017/7/7
https://doi.org/10.1186/s40645-017-0132-y― 74 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes
Hasegawa A, Nakajima J[Keywords] Internal slab structure, slab metamorphism, dehydration-related embrittlement, intermediate-depth
earthquake, intraslab earthquake, earthquake generation mechanism, subduction zone

We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab
metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events forma double seismic zone in the depth range of c. 40–180 km,
which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial
distributions of these events and a close relationship with slab
metamorphism. Pressure–temperature paths of the crust for coldslabs encounter facies boundaries with large H2O production
rates and positive total volume change, which are expected tocause highly active seismicity near the facies boundaries. A beltof upper-plane seismicity in the crust nearly parallel to 80–90
km depth contours of the slab surface has been detected in
the cold Pacific slab beneath eastern Japan, and is probably
caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists
down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at thisFig. 1 (a) P–T paths of the subducting crust for six subduction zones. Shading shows maximum H2O contents
in wt%. (b) Accumulated dehydration-derived H2O content in wt%, (c) rate of H2O production and (d) total

depth. Similar low-velocity subducting crust closely related withsystem (solid + H2O) volume for Hokkaido (blue lines)

intraslab seismicity has been detected in several other subduc-

as a representative cold slab, and for Kii (red lines) astion zones. Seismic tomography studies in NE Japan and north-a representative warm slab. In (c), Kii is scaled by aern Chile also revealed the presence of a P-wave low-velocity

factor of 10. (e) Frequency of upper-plane earthquakes

layer along the lower plane of a double seismic zone. However,

beneath central Hokkaido as a function of depth.

in contrast to predictions based on the serpentinized mantle,
S-wave velocity along this layer is not low. Seismic anisotropy
and pore aspect ratio may play a role in generating this uniquestructure. Although further validation is required, observationsof these distinct low P-wave velocities along the lower seismic
plane suggest the presence of hydrated rocks or fluids withinthat layer. These observations support the hypothesis that dehy-

Fig. 2 (a) S-wave velocity distribution and (b) earth-dration-derived H2O causes intermediate-depth intraslab earth-quake hypocenters within the crust of the Pacific slab. A

quakes. However, it is possible that dual mechanisms generatethese earthquakes; the initiation of earthquake rupture may becaused by local excess pore pressure from H2O, and subsequent ruptures may propagate through thermal shear instability.

belt of upper-plane seismicity is shown in pink. Broken
black curves denote iso-depth contours of the upper
plate surface. The slab–slab contact zone between the
Pacific and Philippine Sea slabs is enclosed by two
green broken curves.

In either case, slab-derived H2O plays an important role in generating intermediate-depth events.
Published: 2017/4/10
https://doi.org/10.1186/s40645-017-0126-9― 75 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Imaging in 3D under pressure: a decade of high-pressure X-ray microtomography development
at GSECARS
Yu T, Wang Y, Rivers M L[Keywords] High pressure, Tomography, Synchrotron, Density, Rotation, Shear, Non-crystalline, Elasticity

The high-pressure X-ray microtomography(HPXMT) apparatus has been operating at
the GeoSoilEnviroCARS (GSECARS) bending magnet beamline at the Advanced Photon
Source since 2005. By combining the powerfulsynchrotron X-ray source and fast switching
between white (for X-ray diffraction) and monochromatic (for absorption imaging) modes, thistechnique provides the high-pressure community with a unique opportunity to image thethree-dimensional volume, texture, and microstructure of materials under high pressure andtemperature. The ability to shear the sample
with unlimited strain by twisting the two opposedanvils in the apparatus allows shear deformation studies under extreme pressure and temperature to be performed. HPXMT is a powerfultool for studying the physical properties of both
crystalline and non-crystalline materials underhigh pressure and high temperature. Over the
past 10 years, continuous effort has been put
into technical development, modifications toimprove the overall performance, and additional
probing techniques to meet users’ needs. Here,
we present an up-to-date report on the HPXMT

Evolution of FeS melt distribution in the olivine matrix by shear deformation.

system, a brief review of some of its many exciting scientific applications, and a discussion of
future developments.

Published: 2016/6/8
https://doi.org/10.1186/s40645-016-0093-6― 76 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Philippine Sea Plate inception, evolution and consumption with special emphasis on the earlystages of Izu-Bonin-Mariana subduction
Lallemand S[Keywords] Philippine Sea Plate, Izu-Bonin-Mariana, subduction initiation, boninite, fore-arc basalt, serpentinite mud
volcano, back-arc basin, transform fault, arc terrane, plume-ridge interaction

We compiled the most relevant data acquired throughout the Philippine Sea Plate (PSP) from the early expeditions to the most recent. We also analyzed the various
explanatory models in light of this updated dataset. The
following main conclusions are discussed in this study.
(1) The Izanagi slab detachment beneath the East
Asia margin around 60–55 Ma likely triggered the OkiDaito plume occurrence, Mesozoic proto-PSP splitting,shortening and then failure across the paleo-transformboundary between the proto-PSP and the Pacific Plate,
Izu-Bonin-Mariana subduction initiation and ultimately
PSP inception. (2) The initial splitting phase of the composite proto-PSP under the plume influence at ~54–48
Ma led to the formation of the long-lived West Philippine
Basin and short-lived oceanic basins, part of whose
crust has been ambiguously called “fore-arc basalts”(FABs). (3) Shortening across the paleo-transformboundary evolved into thrusting within the Pacific Plate
at ~52–50 Ma, allowing it to subduct beneath the newly
formed PSP, which was composed of an alternance ofthick Mesozoic terranes and thin oceanic lithosphere.
(4) The first magmas rising from the shallow mantle
corner, after being hydrated by the subducting Pacificcrust beneath the young oceanic crust near the upper
plate spreading centers at ~49–48 Ma were boninites.
Both the so-called FABs and the boninites formed at asignificant distance from the incipient trench, not in afore-arc position as previously claimed. The magmas

Schematic tectono-magmatic model of IBM subduction initiationand early evolution. Special emphasis has been done on the geodynamic context of various magma1 eruptions. The white lines in

erupted for 15 m.y. in some places, probably near thestage “40 Ma - present” represent the former positions of plateintersections between back-arc spreading centers andboundaries or the base of the upper plate in stage “45-40 Ma”.

the arc. (5) As the Pacific crust reached greater depths

TF = transform fault, PAC = Pacific, FAB = Forearc basalts

and the oceanic basins cooled and thickened at ~44–
45 Ma, the composition of the lavas evolved into high-Mg andesites and then arc tholeiites and calc-alkaline andesites.
(6) Tectonic erosion processes removed about 150–200 km of frontal margin during the Neogene, consuming mostor all of the Pacific ophiolite initially accreted to the PSP. The result was exposure of the FABs, boninites, and earlyvolcanics that are near the trench today. (7) Serpentinite mud volcanoes observed in the Mariana fore-arc may haveformed above the remnants of the paleo-transform boundary between the proto-PSP and the Pacific Plate.
Published: 2016/5/12
https://doi.org/10.1186/s40645-016-0085-6― 77 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Mantle hydration and Cl-rich fluids in the subduction forearc
Reynard B[Keywords] Subduction, Fluids, Forearc mantle, Salinity, Chlorine

In the forearc region, aqueous fluids are
released from the subducting slab at a ratedepending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plateinterface or the Moho of the overriding plate.
Channeling of fluids along the plate interface
and Moho may result in fluid overpressure in
the oceanic crust, precipitation of quartz fromfluids, and low Poisson ratio areas associatedwith tremors. Above the subducting plate, theforearc mantle wedge is the place of intense
reactions between dehydration fluids from thesubducting slab and ultramafic rocks leading
to extensive serpentinization. The plate inter-

Potential location of high-salinity fluids in the forearc mantle and pathwaysof mixing with hotsprings and the volcanic arc. Magnetotelluric profiles in
the Cascadia subduction (Wannamaker, et al. 2014) are shown on theright and are interpreted on the left. The southernmost section shows theface is mechanically decoupled, most likely inhighest conductivity in the forearc (green ellipse) that is interpreted as up

relation to serpentinization, thereby isolatingto 1 m NaCl fluids using diagrams in Fig. 2. Lower forearc conductivities

the forearc mantle wedge from convection as(green ellipses) on the other two sections indicate dilution by more thana cold, potentially serpentinized and buoyant,

one order of magnitude by low-salinity dehydration fluids from the slab or abody. Geophysical studies are unique probes
to the interactions between fluids and rocks inthe forearc mantle, and experimental constrains
on rock properties allow inferring fluid migration

decrease by more than one order of magnitude of the fluid fraction. This is
attributed drainage to shallow aquifers above the forearc region (e. g., theWillamette basin in Oregon, WB) or to the volcanic arc (VA) region (green
arrows). High-conductivity regions further east are ascribed to melt-richregions under the volcanic arc (red ellipses)and fluid-rock reactions from geophysical data.
Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little
serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amountof water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data frompetrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis
and interpretation of seismic data. Electrical conductivity increases with increasing fluid content and temperature of
the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not
only with the thermal state of the subduction zone, but also with time for a given thermal state through variations of
fluid salinity. High-Cl fluids produced by serpentinization can mix with the source rocks of the volcanic arc and explain
geochemical signatures of primitive magma inclusions. Signature of deep high-Cl fluids was also identified in forearc
hot springs. These observations suggest the existence of fluid circulations between the forearc mantle and the hotspring hydrothermal system or the volcanic arc. Such circulations are also evidenced by recent magnetotelluric profiles.

Published: 2016/4/28
https://doi.org/10.1186/s40645-016-0090-9― 78 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Iron snow, crystal floats, and inner-core growth: modes of core solidification and implications for
dynamos in terrestrial planets and moons
Breuer D, Rueckriemen T, Spohn T[Keywords] Core crystallization, Dynamo generation, Iron snow, Terrestrial planets, Thermal evolution

Recent planetary space missions, new experimental
data, and advanced numerical techniques have helped
to improve our understanding of the deep interiorsof the terrestrial planets and moons. In the present
review, we summarize recent insights into the stateand composition of their iron (Fe)-rich cores, as well
as recent findings about the magnetic field evolutionof Mercury, the Moon, Mars, and Ganymede. Crystallizing processes in iron-rich cores that differ from theclassical Earth case (i.e., Fe snow and iron sulfide(FeS) crystallization) have been identified and foundto be important in the cores of terrestrial bodies. The
Fe snow regime occurs at pressures lower than thatin the Earth’s core on the iron-rich side of the eutectic, where iron freezes first close to the core–mantle
boundary rather than in the center. FeS crystallization,
instead, occurs on the sulfur-rich side of the eutectic.
Depending on the core temperature profile and thepressure range considered, FeS crystallizes either inthe core center or close to the core–mantle boundary.
The consequences of the various crystallizing mechanisms for core dynamics and magnetic field generation
are discussed. For the Moon, revised paleomagnetic
data obtained with advanced techniques suggest apeculiar history of its internal dynamo, with an earlystrong field persisting between 4.25 and 3.5 Ga, andsubsequently a much weaker field. In addition, thelong-lasting dynamo and the possible presence of an
inner core, as inferred from a revised interpretation of
Apollo seismic data, suggest core crystallization as a
viable process of magnetic field generation for a substantial period during lunar evolution. The present-day
magnetic fields of Mercury and Ganymede (if theyoccur on the iron-rich side of the Fe–FeS eutectic)
and the related dynamo action are likely generated in
the Fe snow regime and seem to be recent features.
An earlier dynamo in Mercury would have been powered differently. For Mercury, MESSENGER data further suggest core formation under reducing conditions
that may have resulted in an Fe–S–Si composition,

Crystallization scenarios in the Fe–FeS system. Crystallization scenarios in the Fe–FeS system. a Earth-like, Fe-rich inner core grows
from the center. Sulfur is enriched in the outer core and drives
chemical convection. b Iron snow forms at the CMB, sinks, andremelts at depth and drives chemical convection. The stable snow
zone grows in time. When it reaches the center, an inner solidcore will form. c Floating FeS crystals form a stable zone growing
toward the CMB where eventually a solid FeS layer will form. The
fluid below is enriched in iron and unstable to convection. d A solid
FeS layer grows from the CMB. Expulsion of Fe results in chemical
convection in the fluid below as in (c). e FeS crystals rise from thecenter and remelts at lower depths. The liquid above the FeS zone
is convectively unstable. When the FeS crystal zone reaches the
CMB, a solid FeS layer will form. f Fe3S snow forms at the CMB
and the chemically unstable snow zone grows until it comprises theentire core where a solid Fe3S inner core will form. The layer below
is chemically homogeneous but may convect thermally. g A solid
Fe3S inner core grows with time without the release of chemical
buoyancy to the outer core and convection above. Red, green, andblue dots indicate solid iron, solid FeS, and Fe3S, respectively.
Short dashes show the direction of sinking or rising. Red solidlines are the core temperature, blue dashed lines the core melting temperature, and black solid lines the concentration of sulfur,
respectively. Solid arrows indicate chemical and dashed arrows
thermal convection, respectively. For further explanation, see text.

further complicating the core crystallization process.
Mars, with its early and strong paleo-field, likely has
not yet started to freeze out an inner iron core.

Published: 2015/11/16
https://doi.org/10.1186/s40645-015-0069-y― 79 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Liquid Sodium Models of the Earth’s Core
Adams M M, Stone D R, Zimmerman D S, Lathrop D P[Keywords] Magnetic dynamos, Fluid experiments, Geodynamo, Magnetic induction, Zonal flows, Turbulence,
Experimental fluid dynamos, Spherical Couette flow

Our understanding of the dynamics of the Earth’s core canbe advanced by a combination of observation, experiments,and simulations. A crucial aspect of the core is the interplay
between the flow of the conducting liquid and the magnetic
field this flow sustains via dynamo action. This non-linear
interaction, and the presence of turbulence in the flow, precludes direct numerical simulation of the system with realistic
turbulence. Thus, in addition to simulations and observations(both seismological and geomagnetic), experiments can contribute insight into the core dynamics. Liquid sodium laboratory experiments can serve as models of the Earth’s corewith the key ingredients of conducting fluid, turbulent flow,
and overall rotation, and can also approximate the geometryof the core. By accessing regions of parameter space inaccessible to numerical studies, experiments can benchmark
simulations and reveal phenomena relevant to the Earth’s
core and other planetary cores. This review focuses on the
Rendering of the 3 m experiment. The inner sphere and theparticular contribution of liquid sodium spherical Couetteouter spherical shell can be driven independently by theirdevices to this subject matter.

two respective motors (top). Liquid sodium serves as theworking fluid for hydromagnetic experiments

Published: 2015/9/17
https://doi.org/10.1186/s40645-015-0058-1― 80 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos
Amit H, Choblet G, Olson P, Monteux J, Deschamps F, Langlais B, Tobie G[Keywords] Magnetic field, Dynamo, Core-mantle boundary, Heat flux

Mantle control on planetary dynamos is often
studied by imposing heterogeneous core-mantle boundary (CMB) heat flux patterns on theouter boundary of numerical dynamo simulations. These patterns typically enter two maincategories: Either they are proportional to seismic tomography models of Earth’s lowermost
mantle to simulate realistic conditions, or they
are represented by single spherical harmonics
for fundamental physical understanding. However, in reality the dynamics in the lower mantle is much more complicated and these CMB
heat flux models are most likely oversimplified.

Top: Geomagnetic reversal frequency (yellow and barcode below) basedon the Geomagnetic Polarity Time Scale (GPTS) database vs. reversal
frequency in dynamo models with time-dependent CMB heat flux (black

Here we term alternative any CMB heat flux pat-pluses) and fixed present-day tomographic pattern (red crosses). The Cre-tern imposed on numerical dynamos that does

taceous Normal Superchron (CNS), Kiaman Reversed Superchron (KRS)

not fall into these two categories, and insteadand Moyero Reversed Superchron (MRS) are grey shaded.

attempts to account for additional complexity
in the lower mantle. We review papers that

Bottom: Polarity bias, i.e. the difference between time spent in normal andreversed polarities normalized by their sum.

attempted to explain various dynamo-related
observations by imposing alternative CMB heat flux patterns on their dynamo models. For present-day Earth, the alternative patterns reflect non-thermal contributions to seismic anomalies or sharp features not resolved by global tomography models. Time-dependent mantle convection is invoked for capturing past conditions on Earth’s CMB. For Mars,
alternative patterns account for localized heating by a giant impact or a mantle plume. Recovered geodynamo-related
observations include persistent morphological features of present-day core convection and the geomagnetic field aswell as the variability in the geomagnetic reversal frequency over the past several hundred Myr. On Mars the models
aim at explaining the demise of the paleodynamo or the hemispheric crustal magnetic dichotomy. We report the main
results of these studies, discuss their geophysical implications, and speculate on some future prospects.

Published: 2015/9/9
https://doi.org/10.1186/s40645-015-0056-3― 81 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison with seismic models
Antonangeli D, Ohtani E[Keywords] Sound velocity measurements, High pressure, hcp-Fe, Extrapolation schemes, Earth’s inner core,
Comparison with seismic models

Determining the sound velocity of iron under
extreme thermodynamic conditions is essential
for a proper interpretation of seismic observations of the Earth’s core but is experimentallychallenging. Here, we review techniques andmethodologies used to measure sound velocities in metals at megabar pressures, withspecific focus on the compressional soundvelocity of hexagonal close-packed iron. A critical comparison of literature results, coherently
analyzed using consistent metrology (pressure
scale, equation of state), allows us to propose
reference relations for the pressure and density dependence of the compressional velocityof hexagonal close-packed iron at ambient temperature. This provides a key base line upon

Figure 1: Various previous experimental data on sound velocity and density of hcp-Fe are corrected based on the same pressure scale and thewhich to add complexity, including high-tem-

equation of state of hcp-Fe. Most of previous data are consistent withperature effects, pre-melting effects, effects ofeach other.

nickel and/or light element incorporation, necessary for an accurate comparison with seismic
models, and ultimately to constrain Earth’s innercore composition.

Figure 2: Compressional sound velocity as a function of density under
static compression at 300 K is compared with the shock wave data along
Hugoniot. The temperature effect on the Birch’s law is clearly observedin this figure.

Published: 2015/3/13
https://doi.org/10.1186/s40645-015-0034-9― 82 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms
Ujiie K, Kimura G[Keywords] Subduction earthquake, Accretionary prism, Fault rock, NanTroSEIZE

Subduction earthquakes on plate-boundary
megathrusts accommodate most of the global
seismic moment release, frequently resulting
in devastating damage by ground shaking andtsunamis. As many earthquakes occur in deepsea regions, the dynamics of earthquake faulting in subduction zones is poorly understood.
However, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone
Experiment (NanTroSEIZE) and fault rock studies in accretionary prisms exhumed from source
depths of subduction earthquakes have greatly
improved our understanding of earthquake
faulting in subduction zones. Here, we review
key advances that have been made over theConcept of earthquake faulting in subduction zones shown in schematic
profile of the Nankai accretionary prism.

last decade in the studies of fault rocks and inlaboratory experiments using fault zone materials, with a particular focus on the Nankai Trough subduction zone andits on-land analog, the Shimanto accretionary complex in Japan. New insights into earthquake faulting in subduction
zones are summarized in terms of the following: (1) the occurrence of seismic slip along velocity-strengthening materials both at shallow and deep depths; (2) dynamic weakening of faults by melt lubrication and fluidization, and possible
factors controlling coseismic deformation mechanisms; (3) fluid-rock interactions and mineralogical and geochemicalchanges during earthquakes; and (4) geological and experimental aspects of slow earthquakes.

Published: 2014/6/3
https://doi.org/10.1186/2197-4284-1-7― 83 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Solid earth sciences

Water-melt interaction in hydrous magmatic systems at high temperature and pressure
Bjorn Mysen[Keywords] Hydrous magma, Aqueous fluid, Melt structure, Viscosity, Isotope partitioning, Partial melting, Water
solubility, Silicate solubility, Glass transition, Solution mechanism

Experimental data on the structure and propertiesof melts and fluids relevant to water-melt interaction
in hydrous magmatic systems in the Earth’s interior
have been reviewed. Complex relationships between
water solubility in melts and their bulk composition [Al/Si-ratio, metal oxide/(Al + Si) and electron propertiesof metal cations] explain why water solubility in felsicmagmas such as those of rhyolite and andesite composition is significantly greater than the water solubility
in basalt melts. The silicate solubility in aqueous fluid isalso significantly dependent on composition with metaloxide/(Al + Si) and electron properties of the metal cations, the dominant variables. Hydrogen bonding is notimportant in hydrous fluids and melts at temperatures
above 500°C to 550°C and does not, therefore, playa role in hydrous magmatic systems. The properties
of hydrous melts and aqueous solutions are governedby how the silicate speciation (Qn species, where n is
the number of bridging oxygen in an individual species)
varies with bulk composition, silicate composition, temperature, and pressure. The reactions that describe theinteractions are similar in melts, fluids, and supercriti-

Schematic representation of the concept of bridging (BO) andnonbridging (NBO) oxygencal fluids. The degree of melt polymerization caused bydissolved water varies with melt composition and total
water content. Silicate- and alkali-rich felsic magmatic
melts are more sensitive to water content than more
mafic magmas. Transport and configurational properties of hydrous magmatic melts can be modeled withthe aid of the Qn speciation variations. Liquidus andmelting phase relations of hydrous systems also canbe described in such terms, as can minor and traceelement partition coefficients. Stable isotope fractionation (e.g., D/H) can also be rationalized in this manner.
Critical to these latter observations is the high silicate
concentration in aqueous fluids. These components
can enhance solubility of minor and trace elements

Degree of silicate polymerization, NBO/T. In silicate in hydrous

by orders of magnitude and change the speciation ofmelts, silicate-saturated aqueous fluid, and supercritical fluid in a

H and D complexes so that their fractionation factors

hydrous Na-aluminosilicate systemchange quite significantly. Data from pure silicate-H2O
systems cannot be employed for these purposes.

Published: 2014/4/22
https://doi.org/10.1186/2197-4284-1-4― 84 ―

Review
Interdisciplinary researchProgress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Identifying key processes and sectors in the interaction between climate and socio-economic
systems: a review toward integrating Earth–human systems
Tachiiri K, Su X, Matsumoto K[Keywords] Earth system model, Integrated assessment model, Socio-economic system, Climate system, HumansystemFor the purpose of identifying the key processes and sectors involved in the interaction
between Earth and socio-economic systems,
we review existing studies on those processes/
sectors through which the climate impacts
socio-economic systems, which then in turnaffect the climate. For each process/sector, we
review the direct physical and ecological impacts
and, if available, the impact on the economy
and greenhouse gas (GHG) emissions. Basedon this review, land sector is identified as theprocess with the most significant impact on
GHG emissions, while labor productivity has thelargest impact on the gross domestic productConceptual diagram of the Earth-human (socio-economic) system inter-(GDP). On the other hand, the energy sector,

action.

due to the increase in the demand for cooling,
will have increased GHG emissions. Water resources, sea level rise, natural disasters, ecosystem services, and diseases also show the potential to have a significant influence on GHG emissions and GDP, although for most of these,a large effect was reported only by a limited number of studies. As a result, more studies are required to verify theirinfluence in terms of feedbacks to the climate. In addition, although the economic damage arising from migration andconflict is uncertain, they should be treated as potentially damaging processes.

Published: 2021/4/8
https://doi.org/10.1186/s40645-021-00418-7― 86 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Coupling library Jcup3: its philosophy and application
Arakawa T, Inoue T, Yashiro H, Satoh M[Keywords] Earth system modeling, Coupler, Coupled simulation

In this paper, we describe the design of thecoupling library, Jcup, and report its various
applications, including the coupling between
global atmospheric and oceanic models of different grid systems. Jcup is a software library
mainly focused on weather/climate models andwas developed for coupling the components ofvarious models. Jcup has the flexibility to be
applied to an unspecified number of components of earth system models. To achieve ahigh level of safety and versatility, we classified
the processes of the general coupling software

Data exchange diagram. The gray circles represent masked value. There-

into processes that change the value of the data

fore, only the grid point value indicated by the blue circle is passed fromand those that do not and placed the former

Component A to Component B.

outside of the program and under the controlof the user. Consequently, Jcup exhibits two features: (1) the correspondence relationship between grid indexes isused as input information, and (2) the user can implement an arbitrary interpolation code. Jcup was applied to atmosphere-ocean coupling, IO component coupling, and the coupling between the seismic model and structure model,
and the validity and usefulness of the design were demonstrated.

Published: 2020/2/6
https://doi.org/10.1186/s40645-019-0320-z― 87 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Morphometric measurements of bedrock rivers at different spatial scales and applications togeomorphological heritage research
Gomez-Heras M, Ortega-Becerril JA, Garrote J, Fort R, Lopez-Gonzalez L[Keywords] Bedrock rivers, Geomorphological heritage, Non-destructive techniques, Digital elevation models, LiDAR,
SfM, Photogrammetry, Microroughness

Morphometric characterisation is particularly relevant in the study of geomorphological
heritage. 3D modelling techniques have been
proven as very useful tools to recognise, characterise and valorise geomorphosites. Bedrock
rivers account for one of the most outstanding aspects within geomorphological heritage
due to the amount of distinctive and attractive
geomorphological features associated to themand the high preservation of sculpted forms.
Digital elevation models (DEMs) have made it(a) Example of DEM for different scales of morphometric measurements

increasingly possible to establish accurate mor-in bedrock rivers, (b) Large-scale airborne scan, (c) mesoscale SfM, (d)phometric indices and establish clearer connec-

microscale rugosimetertions between forms and processes. This paper
reviews different methodologies to obtain DEMs on bedrock rivers. This review goes from DEM analysis at multiple
spatial scales to introduce optical microrugosimeter as the latest technical development to facilitate micromorphometricanalysis. Micromorphometric analysis opens the scope for improving the knowledge we have on trans-scale issues in
bedrock rivers. Micromorphometric analysis also opens a new layer of information that enriches the public’s valuationof geodiversity of geomorphosites by increasing its didactic and interpretative potential.

Published: 2019/3/25
https://doi.org/10.1186/s40645-019-0275-0― 88 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary researchNorthern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change
in the twenty-first century
Pavel Groisman et al.
[Keywords] Environmental Changes, Northern Eurasia, Ecosystems dynamics, Terrestrial water cycle, Cryosphereretreat, Extreme and inclement environmental conditions, Sustainable development, Land-cover and land-use change,
Integrated assessment models for decision-makers

During the past several decades, the Earthsystem has changed significantly, especiallyacross Northern Eurasia. Changes in thesocio-economic conditions of the larger countries in the region have also resulted in a variety of regional environmental changes that
can have global consequences. The Northern Eurasia Future Initiative (NEFI) has been
designed as an essential continuation of theNorthern Eurasia Earth Science Partnership
Initiative (NEESPI), which was launched in
2004. NEESPI sought to elucidate all aspects ofongoing environmental change, to inform societies and, thus, to better prepare societies for

Changes in sown areas across the former Soviet Union (Russia, Ukraine,and Kazakhstan) from 1990 to 2013. Areas of abandoned sown areas

future developments. A key principle of NEFI isfor this period are 40 Mha in Russia (Rosstat 2016), 5.4 Mha in Ukrainethat these developments must now be secured(Ukrstat 2014), and 13 Mha in Kazakhstan (Kazstat 2014).

through science-based strategies co-designedwith regional decision-makers to lead their societies to prosperity in the face of environmental and institutional challenges. NEESPI scientific research, data, and models have created a solid knowledge base to support the NEFI
program. This paper presents the NEFI research vision consensus based on that knowledge. It provides the reader
with samples of recent accomplishments in regional studies and formulates new NEFI science questions. To addressthese questions, nine research foci are identified and their selections are briefly justified. These foci include warmingof the Arctic; changing frequency, pattern, and intensity of extreme and inclement environmental conditions; retreatof the cryosphere; changes in terrestrial water cycles; changes in the biosphere; pressures on land use; changes ininfrastructure; societal actions in response to environmental change; and quantification of Northern Eurasia’s role in
the global Earth system. Powerful feedbacks between the Earth and human systems in Northern Eurasia (e.g., megafires, droughts, depletion of the cryosphere essential for water supply, retreat of sea ice) result from past and current
human activities (e.g., large-scale water withdrawals, land use, and governance change) and potentially restrict orprovide new opportunities for future human activities. Therefore, we propose that integrated assessment models areneeded as the final stage of global change assessment. The overarching goal of this NEFI modeling effort will enableevaluation of economic decisions in response to changing environmental conditions and justification of mitigation andadaptation efforts.

Published: 2017/12/27
https://doi.org/10.1186/s40645-017-0154-5― 89 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Cenozoic sedimentary records of climate-tectonic coupling in the Western Himalaya
Clift P D
[Keywords] Monsoon, Climate-tectonic, Himalaya, Erosion, Exhumation, Arabian Sea, Foreland basin, Provenance,
Geochemistry, Cenozoic, Weathering

Sedimentary archives in the Himalayan foreland basin and Indus submarine fan provide themost detailed records of how changing monsoon strength may have affected erosion andthe development of tectonic structures in thewestern Himalaya during the Neogene. Muscovite Ar-Ar ages show that fast exhumation of
the Greater Himalaya was earlier in the west
(20–35 Ma) than in the central Himalaya (10–25Ma), probably driven by progressive lithosphericslab tearing that caused both rock uplift and an

The correlation between the uplift of the Himalaya-Tibetan Plateau andthe Asian monsoon

intensified summer monsoon to start earlier inthe western Himalaya. Rates of exhumation reduced after ~17 Ma as uplift also slowed, apparently unrelated to climatechange. However, further reduction at 6–8 Ma coincided with a time of weakening summer rains, as shown by carbon
isotope data from the foreland and hematite-goethite records from ODP Site 730 on the Oman margin. Coming at atime of stronger winds, this drying was linked to global climatic cooling. Weakening of Late Miocene monsoon rains
coincided with a southward migration of the ITCZ and faster erosion of the Lesser rather than Greater Himalaya.
Unroofing of the Inner Lesser Himalaya, starting after 9 Ma, followed as a consequence of duplex formation enabled
by focused erosion, although widespread exposure of that range was delayed until after 6 Ma. Inner Lesser Himalayan
exposure, combined with unroofing of the Nanga Parbat Massif, caused a decrease in average εNd values of Indus
River sediment after 5 Ma, rather than large-scale drainage capture.

Published: 2017/12/14
https://doi.org/10.1186/s40645-017-0151-8― 90 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Transitional changes in microfossil assemblages in the Japan Sea from the Late Pliocene to
Early Pleistocene related to global climatic and local tectonic events
Itaki T
[Keywords] Radiolaria, Diatom, Calcareous nannofossil, Foraminifera, Ostracoda, Productivity, Paleoceanography,
Northern Hemisphere glaciation, Tectonics, Tsushima Warm Current

Many micropaleontological studies basedon data from on-land sections, oil wells, anddeep-sea drilling cores have provided important information about environmental changes
in the Japan Sea that are related to the global
climate and the local tectonics of the JapaneseIslands. Here, major changes in the microfossil
assemblages during the Late Pliocene to Early
Pleistocene are reviewed. Late Pliocene (3.5–
2.7 Ma) surface-water assemblages were characterized mainly by cold–temperate planktonic
flora and fauna (nannofossils, diatoms, radiolarians, and planktonic foraminifera), suggestingthat nutrient-rich North Pacific surface waters
entered the Japan Sea via northern straits. The
common occurrence of Pacific-type deep-water

Schematic maps showing paleogeographic changes in the Japan Sea
during three stages. Solid arrows show major inflows of oceanic water,and dashed arrows indicate restricted inflows.

radiolarians during this period also suggeststhat deep water from the North Pacific entered the Japan Sea via the northern straits, indicating a sill depth >500 m.
A weak warm-water influence is recognized along the Japanese coast, suggesting a small inflow of warm water via
a southern strait. Nannofossil and sublittoral ostracod assemblages record an abrupt cooling event at 2.75 Ma that
correlates with the onset of the Northern Hemisphere glaciation. Subsequently, cold intermediate- and deep-water
assemblages of ostracods and radiolarians increased in abundance, suggesting active ventilation and the formationof the Japan Sea Proper Water, associated with a strengthened winter monsoon. Pacific-type deep-water radiolarians
also disappeared around 2.75 Ma, which is attributed to the intermittent occurrence of deep anoxic environments
and limited migration from the North Pacific, resulting from the near-closure or shallowing of the northern strait bya eustatic fall in sea level and tectonic uplift of northeastern Japan. A notable reduction in primary productivity from
2.3 to 1.3 Ma also suggests that the nutrient supply from the North Pacific was restricted by the near-closure of thenorthern strait. An increase in the abundance of subtropical surface fauna suggests that the inflow of the Tsushima
Warm Current into the Japan Sea via a southern strait began at 1.7 Ma. The opening of the southern strait may haveoccurred after the subsidence of southwestern Japan.

Published: 2016/5/5
https://doi.org/10.1186/s40645-016-0087-4― 91 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Evolution and variability of the Asian monsoon and its potential linkage with uplift of theHimalaya and Tibetan Plateau
Tada R, Zheng H, Clift P D[Keywords] East Asian summer monsoon, East Asian winter monsoon, Indian summer monsoon, Himalaya, Tibetan
Plateau, Chinese Loess Plateau, Climate model, Tectonic–climate linkage, Westerly jet, Desertification

In the densely populated region of East Asia,
it is important to know the mechanism, scale,and frequency of heavy precipitation brought
about during the monsoons and typhoons.
However, observational data, which cover only
several decades, are insufficient to examine thelong-term trend of extreme precipitation and its
background mechanism. In humid areas, thetransport flux of a suspended detrital material
through a river system is known to have an
empirical power relationship with precipitation.
Thus, the sedimentation flux of a fine detritalmaterial could potentially be used as a proxy forreconstructing past heavy precipitation events.

Evolution of Asian monsoons, desertification, HTP uplift, and their rela-

To test the idea that the sedimentation flux oftion with global changes during Cenozoic. Temporal changes of a δ18O

detrital materials records past heavy precipitation events (e.g., typhoons), we focused on
the detrital flux estimated from the annuallyof benthic foraminifera (modified from Zachos et al. 2001) and b pCO2
(modified from Zhang et al. 2013) are compared with temporal evolutionof c Asian monsoons, d desertification, e HTP uplift, and f associatedtectonic events. In c and e, gray bars represent weak phases and black

laminated sediment of Lake Suigetsu, central

bars represent strong phases. In d, JuB and TaB indicate Jungger BasinJapan, which is capable of accurately correlat-

and Tarim Basin, respectively.

ing the age of detrital flux with the precipitation
record. We first established a precise age model (error within ±1 year in average) beginning in 1920 A.D. on the basisof varve counting fine-tuned by correlation between event layers with historical floods. The flux of the detrital material(g/cm2/year) was estimated on the basis of Al2O3 content (wt%), dry bulk density (g/cm3), and sedimentation rate (cm/year) calculated from the age model. The detrital flux of background sedimentation showed a weak positive correlation
with annual and monthly (June and September) precipitation excluding heavy precipitation that exceeded 100 mm/day.
Furthermore, the thickness of instantaneous event layers, which corresponds to several maxima of detrital flux and iscorrelated with floods that occurred mainly during typhoons, showed a positive relationship with the total amount ofprecipitation that caused a flood event. This result suggests that the detrital flux maxima (deposition of event layers)
record past extreme precipitation events that were likely associated with typhoons that hit the middle part of Honshu
Island. Based on this result, the record of typhoon-caused flood events can go back to older period (e.g., last glacial
period) on the basis of the occurrence, and thickness, or mass flux of event layers using long sediment cores from
Lake Suigetsu.

Published: 2016/2/9
https://doi.org/10.1186/s40645-016-0080-y― 92 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Geochemical approaches to the quantification of dispersed volcanic ash in marine sediment
Scudder R P, Murray R W, Schindlbeck J C, Kutterolf S, Hauff F, Underwood M B, Gwizd S, Lauzon R,
McKinley C C[Keywords] Dispersed ash, Caribbean Sea, Equatorial Pacific Ocean, Northwest Pacific Ocean, Ash layers, Volcanic
eruptions, DSDP, ODP, IODP

Volcanic ash has long been recognized inmarine sediment, and given the prevalence of
oceanic and continental arc volcanism aroundthe globe in regard to widespread transport ofash, its presence is nearly ubiquitous. However,the presence/absence of very fine-grained ash
material, and identification of its composition inparticular, is challenging given its broad classification as an “aluminosilicate” component insediment. Given this challenge, many studies
of ash have focused on discrete layers (that is,layers of ash that are of millimeter-to-centimeteror greater thickness, and their respective glass
shards) found in sequences at a variety of locations and timescales and how to link their presence with a number of Earth processes. The
ash that has been mixed into the bulk sediment,
known as dispersed ash, has been relatively
unstudied, yet represents a large fraction of
the total ash in a given sequence. The application of a combined geochemical and statistical technique has allowed identification of thisdispersed ash as part of the original ash contribution to the sediment. In this paper, we summarize the development of these geochemical/
statistical techniques and provide case studies
from the quantification of dispersed ash in the
Caribbean Sea, equatorial Pacific Ocean, andTop: Global distribution of subaerial volcanoes in different tectonic settings. Map has been modified after http://d-maps.com and volcano positions are taken from the Smithsonian Global Volcanism Program (http://

northwest Pacific Ocean. These geochemicalwww.volcano.si.edu).

studies (and their sedimentological precursors

Bottom: Locations of sites highlighted in this paper. Data from GeoMa-of smear slides) collectively demonstrate that

pApp (http://www.geomapapp.org; GMRT-Global Multi-Resolution Topog-

local and regional arc-related ash can be an

raphy; Ryan et al., 2009)

important component of sedimentary sequences
throughout large regions of the ocean.

Published: 2016/1/4
https://doi.org/10.1186/s40645-015-0077-y― 93 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Sea surface temperature proxies (alkenones, foraminiferal Mg/Ca, and planktonic foraminiferal
assemblage) and their implications in the Okinawa TroughKim R A, Lee K E, Bae S W[Keywords] Sea surface temperature, Okinawa Trough, Alkenone, Planktonic foraminiferal Mg/Ca ratio, Planktonic
foraminiferal assemblages

We reviewed three sea surface temperature(SST) proxies in the Okinawa Trough (OT):
alkenones, planktonic foraminiferal Mg/Ca, andplanktonic foraminiferal assemblages. The seasonal and vertical distribution patterns of eachproxy-related organism in the water column
were reviewed to confirm the applicability ofeach proxy. In addition, current SSTs (Japan
Oceanographic Data Center dataset from 1906
to 2003) were compared with core-top sedimenttemperatures reconstructed using the proxies.

Schematic diagram of SST proxy data in the OT. SST proxy data are given
for periods during the late Holocene (0–3 cal kyr BP) and LGM (18–21 cal
kyr BP). T indicates temperature.

Temperatures calculated using the alkenone
unsaturation index represent annual mean SSTs, and temperatures calculated using Mg/Ca of Globigerinoides ruber
capture summer to autumn (June–November) SSTs. Core-top August SSTs calculated from planktonic foraminiferal
assemblages corresponded well with the observed SSTs, but core-top February temperatures were ~3.6 °C warmer
than the observed SSTs. SST proxy estimates from marine sediments dating back to the late Holocene (0–3 cal ky BP)
and the last glacial maximum (18–21 cal ky BP) were compared. Comparisons between proxy SST estimates showthat foraminiferal assemblage-based August SSTs were the warmest. Alkenone-based temperature estimates werelower than Mg/Ca-based temperature estimates, probably because the alkenone-based temperature represents theannual mean temperature, whereas the Mg/Ca-based temperature represents the summer–autumn mean temperature.
February assemblage SSTs seem to be greatly affected by the statistical technique and/or database used. These
results suggest that seasonality should be considered in past SST reconstruction using alkenone and Mg/Ca in the
OT. The planktonic foraminiferal assemblage technique does not appear to be promising with respect to accurately
reconstructing past SSTs (especially winter) in the OT. Habitat depth may not be an issue because both alkenone
producers and G. ruber live at the upper surface mixed layer in the area.
Glacial–interglacial changes in the surface hydrography of the OT reconstructed based on the SST and salinity
proxies were also reviewed here. The surface hydrography of the OT has been influenced by changes in the Kuroshio
Current and the East Asian monsoon system during the late Quaternary. Comparisons of the hydrography records
from the OT with records of stalagmites in China, the Tropical Pacific, and the North Atlantic show that there is ateleconnection between them.

Published: 2015/12/1
https://doi.org/10.1186/s40645-015-0074-1― 94 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

Marine tephra in the Japan Sea sediments as a tool for paleoceanography and paleoclimatology
Ikehara K[Keywords] Tephra, Key bed, Japan Sea, Stratigraphy, Chronology, Paleoceanography

Tephra is a product of large and explosive volcanic events and can travel thousands of kilometers before deposition. Consequently, tephra
deposits are common in terrestrial, lacustrine,
marine, and glacial environments. Because
tephra deposition is a geologically synchronous
event, tephras constitute important isochronesin the Quaternary sequence, not only in Japanbut also throughout the northwest Pacific andits marginal seas. As a result, establishing thechronostratigraphic order of tephra deposits isan effective tool for assessing local and regional
stratigraphies and for correlating events amongsites. For example, tephrostratigraphy can provide precise chronological constraints for otherDark-layer stratigraphy and tephra occurrences in the late Quaternarystratigraphic data, such as magneto- and bio-

Japan Sea sediments (A) and tephra occurrences in marine sedimentstratigraphic data. Spatiotemporal variability incores during MIS 3−5.3 (B)the occurrence and geochemistry of tephras
can also be used to trace the magmatic evolution of island arcs and their relationships to regional tectonics. In a
paleoclimatic context, tephra deposits allow the correlation of past climate events among terrestrial, lacustrine, andmarine environments. Tephrochronology is also a fundamental element used in reconstructing the marine reservoir
effect, where the ages of tephra in marine and terrestrial settings are compared. Therefore, tephra is a valuable tool
not only in stratigraphy, chronology, and volcanology but also in paleoceanography and paleoclimatology.

Published: 2015/11/16
https://doi.org/10.1186/s40645-015-0068-z― 95 ―

Progress in Earth and Planetary Science
http://progearthplanetsci.org/index.html

Review

Interdisciplinary research

The Pliocene to Recent History of the Kuroshio and Tsushima Currents: a multi-proxy approach
Gallagher S J, Kitamura A, Iryu Y, Itaki T, Koizumi I, Hoiles P[Keywords] Kuroshio Current, Tsushima Current, Pliocene, Pleistocene, Holocene, Paleoceanographic proxies,
Biogeography, Microfossils, Macrofossils, Geochemistry

The Kuroshio Current is a major western boundary current controlled by the North Pacific Gyre. It brings warm subtropical waters from the Indo-Pacific Warm Pool to Japan
exerting a major control on Asian climate. The Tsushima
Current is a Kuroshio offshoot transporting warm water
into the Japan Sea. Various proxies are used to determine the paleohistory of these currents. Sedimentologicalproxies such as reefs, bedforms, sediment source andsorting reveal paleocurrent strength and latitude. Proxies
such as coral and mollusc assemblages reveal past shelfal current activity. Microfossil assemblages and organic/
inorganic geochemical analyses determine paleo- sea surface temperature and salinity histories. Transportation oftropical palynomorphs and migrations of Indo-Pacific spe-

Figure 1: The southern path of the Kuroshio Current showing
the inferred extent of the Ryukyu Reefs in glacial and interglacial periods (adapted from Iryu et al. [2006])

cies to Japanese waters also reveal paleocurrent activity.
The stratigraphic distribution of these proxies suggests theKuroshio Current reached its present latitude (35 °N) by~3 Ma when temperatures were 1 to 2 °C lower than present. At this time a weak Tsushima Current broke throughTsushima Strait entering the Japan Sea. Similar oceanic
conditions persisted until ~2 Ma when crustal stretching
deepened the Tsushima Strait allowing inflow during every
interglacial. The onset of stronger interglacial/glacial cycles~1 Ma was associated with increased North Pacific Gyreand Kuroshio Current intensity. This triggered Ryukyu
Reef expansion when reefs reached their present latitude(~31 °N), thereafter the reef front advanced (~31 °N) andretreated (~25 °N) with each cycle. Foraminiferal proxy
data suggests eastward deflection of the Kuroshio Current
from its present path at 24 °N into the Pacific Ocean due
to East Taiwan Channel restriction during the Last Glacial
Maximum. Subsequently Kuroshio flow resumed its present trajectory during the Holocene. Ocean modeling andgeochemical proxies show that the Kuroshio Current path
may have been similar during glacials and interglacials,
however the glacial mode of this current remains controversial. Paleohistorical studies form important analogues
for current behavior with future climate change, however,there are insufficient studies at present in the region that
may be used for this purpose. Modeling of the response of
the Kuroshio Current to future global warming reveals that

Figure 2: (i) The distribution of G. ruber and Tsushima Current molluscs in interglacials of the Omma Formation (adaptedfrom Kitamura and Kimoto [2006]) correlated to the LR04 benthic stack of Lisiecki and Raymo ([2005]). The red dots (1.6
to 1 Ma) are interglacials where migratory Indo-Pacific Warm
Pool benthic foraminifera are present (Hoiles et al. [2012]). Red
dots at 0 and ~3 Ma are Warm Pool benthic foram ingressions
described in Gallagher et al. ([2009]). Reconstructions of thepaleogeography of the Tsushima Strait after 1.6 Ma (ii) andprior to 1.7 Ma (iii) adapted from Kitamura and Kimoto ([2006])

current velocity may increase by up to 0.3 m/sec associated with a northward migration of the Kuroshio Extension.

Published: 2015/6/27
https://doi.org/10.1186/s40645-015-0045-6― 96 ―

Date of Issue : April, 2023
Correspondence: peps_edit@jpgu.org
Copyright ©2023 PEPS Editorial office All rights reserved.
PEPS is supported by a Grant-in-Aid for Publication of Scientific Research Results (19HP1001) fromJapan Society for the Promotion of Science.