bluuebunny/crossref_metadata_2025 huggingface dataset:
Drones Paired with Hyperspectral Imaging Paired with LiDAR to Locate Explosive Ordnance
Authors: Restrepo Alexandra , Labnine Aya , DiMatteo Rocco , Edwards Colin , Hamilton Jamali , Quinto Luis , Tuohy Madison , Nikulin Alex , de Smet Timothy S.
Published: February 2023

Anti-personal/tank landmines, improvised explosive devices (IED), unexploded ordinances (UXO), and other abandoned explosive ordinances (EO) all pose long-lasting threats that are detrimental to areas of conflict. From 2015 to 2021, a total of 49,050 deaths/injuries were caused by EOs, and this number is only increasing. Current demining methods heavily rely on ground-based electromagnetic-induction (EMI); however, this method is costly, time consuming and puts personnel at risk. Recent advances in drone and remote sensing technology have allowed for the development of alternative remote methods to improve the efficiency in locating EOs. We used a Velodyne VLP-16 light detection and ranging (LiDAR) sensor attached to a DJI Matrice 600 drone platform to remotely identify EOs, specifically PFM-1 and VPMA-3 anti-personnel mines, TM-62M anti-vehicle mines, and 3 meter long 122 mm multibarrel rockets (MBRL). LiDAR data was acquired in dual return acquisition mode at 300 rpm and a flight speed of 1 m/s. Several of these EOs are being used in the current Russo-Ukrainian war, including: TM-62 anti-vehicle mines, PFM-1 landmines, and the MBRL rockets. Our LiDAR sensor was calibrated with a 18 m swath width to acquire 4630 points/m2  density and a 1.7 cm footprint resolution. The LiDAR data that was collected was post-processed to produce various derivative data such as: 3D point clouds, digital elevation models (DEM), digital surface models (DSMs), and derivative data products such as the total horizontal derivative (THD) filter. Processed data highlighted lateral spatial heterogeneity, which identified vertical and horizontal MBRLs, as well as surficial TM-62M anti-vehicle, TM62P anti-personnel mines and VPMA-3 landmines. PFM-1 landmines, the smallest of all EOs used, were not located, as the footprint resolution of the data collected was too small (1.7 cm) to clearly differentiate the ordinance from the environment. This pilot study allowed us to better understand the strengths and weaknesses of this method. We plan to further develop this technology by exploring the use of streamlined algorithms, applying alternative data processing workflows, and using sub-pixel techniques to improve the accuracy and efficiency of location. Refining data acquisition parameters, such as the speed and height of drone flight may also lead to further improvements in efficiency. In addition to location, a focus could also be placed on looking at intensity to identify material properties of EOs. 
Understanding the Coupled OH Meinel and O2 Atmospheric Band Nightglow Emissions
Authors: Kalogerakis Konstantinos S.
Published: February 2023

Nightglow emission signatures observed from space- and ground-based instruments are commonly used as proxies for atmospheric composition, especially for the altitude region around 100 km that cannot be easily studied in situ. Monitoring the intensity and temporal evolution of such proxies by remote sensing is often the method of choice to study a plethora of phenomena in this region of the atmosphere. Thus, the quantitative details relevant to the production and deactivation of excited atomic and molecular precursors responsible for prominent nightglow emissions are required to study atmospheric composition, radiative and energy balance, wave propagation and dissipation, as well as transport dynamics. Significant gaps and uncertainties exist in the understanding of the above processes and, as our recent studies on nightglow emissions revealed, substantial revisions of the relevant atmospheric models are warranted.We will present a progress report on our efforts to advance the understanding of key mesospheric nightglow emissions by investigating the recently established coupling between the OH Meinel and the O2 Atmospheric band emissions, mediated by collisions of O atoms with vibrationally excited OH.This work is supported by the U.S. National Science Foundation (NSF) under Grants AGS-2009960 and AGS-2113888.
Complex morphological changes in marine coarse sediment bedforms
Authors: Ribo Marta , Watson Sally , Mcdonald Helen , Strachan Lorna
Published: February 2023

On inner continental shelves, a variety of coarse grained bedforms, such as gravel dunes, are shaped by hydrodynamic and morphodynamic processes. Repeat, high-resolution, multibeam surveys are crucial to identify geomorphological changes on the seafloor, especially in the extremely dynamic shallow waters (< 200 m water depth). Timeseries bathymetric datasets allow us to measure and monitor spatial- and temporal changes in submarine bedforms and determine their evolution patterns. This is important for a better understanding of the sediment transport processes and the related hydrodynamics, but also to determine the settings for benthic ecosystems and identify changes in seafloor geomorphology to prevent potential damage of offshore infrastructure and maritime pathways.We present three multibeam data sets acquired in 2017, 2020 and 2021 over a field of gravel-sand bedforms located in the high-energy Cook Strait / Te Moana-o-Raukawa. In this study we combine timeseries bathymetric data, ground-truth data (video footage and sediment samples) and oceanographic modelling to understand the sediment dynamics in the area. Results show that coarse sand and gravel field of dunes with superimposed megaripples have undergone intricate morphological changes. The ~100-m length and ~15-m height submarine dune crests bifurcate, becoming more complex between 2017-2020, followed by the reforming of dune crests between 2020-2021. Hydrodynamic modelling suggests there is an interaction between the tidal near-bottom currents and the sediment transport, creating a morphological positive feedback, which might be leading the complex bedform morphological changes observed in the repeated mapping surveys.This study reveals the dynamic nature of the seabed over short time-scales (years) in highly dynamic areas, such as the tidally vigorous Cook Strait region. Our findings demonstrate the importance of repeat multibeam mapping in understanding of the rate and scale of changes on the seafloor.
Modelling the climatology of low- and mid-latitude F-region ionospheric currents using the Swarm constellation
Authors: Fillion Martin , Hulot Gauthier , Alken Patrick , Chulliat Arnaud
Published: February 2023

We present a new empirical model of quiet-time F-region ionospheric currents and associated magnetic fields. This model is designed to accurately represent these currents and fields at low and mid latitudes. It is built by taking advantage of the unprecedented space-time data coverage provided by the Swarm satellite constellation. For each individual Swarm satellite, the preprocessed data is represented as a non-potential toroidal magnetic field using the Mie representation in a thin-shell and spherical harmonic expansions. This approach allows to fully separate spatial and climatological variations as well as to assess the robustness of the model with respect to both measurement errors and data sampling with local time. The obtained model describes the toroidal magnetic fields and the associated radial poloidal electric currents at two distinct altitudes in the ionosphere F region. Clear signatures of low- and mid-latitude interhemispheric field-aligned currents (IHFACs) are identified. The model reproduces well-known characteristics of the climatology of IHFACs and provides new insights, for example on the average daily variations of IHFACs during winter in the northern hemisphere. It also well recovers the variations of IHFACs with longitude. The potential driving mechanisms of these variations, such as longitudinal variations of the main field and modulation by upward propagating atmospheric tides, are discussed. The new model can be used to analyze the relationship between atmospheric tides and IHFACs. It can also be used to investigate the connection between the magnetic fields and electric currents from the ionospheric E and F regions in order to improve the separation of these fields as well as our understanding of the overall ionospheric electric current system.
Coeval stalagmite records from the Rocky Mountains record Holocene climate change
Authors: Belanger Bryce , de Wet Cameron , Sharp Warren , Kinsley Christopher , Cai Yanjun , Oster Jessica
Published: February 2023

Tree ring records show cool-season droughts in the western US have been characterized by three spatial patterns over the past 500 years: “western-wide drought”, “wet north/dry south”, and “dry north/wet south”. Previous work shows that these drought patterns can persist on timescales of decades to centuries and are driven by internal climate variability, with secondary influence by sea surface temperatures. However very few high-resolution records of western US precipitation extend beyond the tree ring record (~1400 CE), limiting our understanding of the occurrence and persistence of these patterns of natural climate variability on longer timescales and further in the past. Here we use trace element (Mg/Ca, Sr/Ca, Ba/Ca, P/Ca) and stable isotope (δ18O, δ13C) data from two coeval stalagmites to construct a Holocene paleoclimate record for Titan Cave (TC), northern Wyoming, extending the hydroclimate record of the northern Rockies and providing the opportunity to assess longer-term natural climate variability in the northern Rockies. The TC-2 and TC-7 speleothems grew over the past ~5.7 ka and ~3.1 ka, respectively. Proxies from both stalagmites exhibit strong correlations with several coeval climate records, including regional snowpack as recorded by tree rings during the past ~600 years, suggesting the speleothems record winter precipitation patterns in the northern Rockies. Decreased snowpack and dry conditions at TC correlate to warmer sea surface temperatures in the Gulf of Alaska and the positive phase of the Pacific Decadal Oscillation. Comparison of speleothem δ18O with the δ18O of Bison Lake sediments from central Colorado suggests all three patterns of western US drought occurred during intervals of the late Holocene. Specifically, the wet north/dry south and dry north/wet south winter precipitation dipoles in the Rocky Mountains with a boundary near 40° N latitude, were established by approximately 3 ka. Multiple, centuries-long “western-wide” droughts occurred throughout the record, most notably from 2.2 – 2 ka during the Roman Warm Period. Other dated TC stalagmites grew during the mid-Holocene and Last Interglacial, providing records of winter precipitation in the northern Rockies during past warm intervals, which may serve as analogs for future anthropogenically-warmed climate states.
Using machine-learning to construct long-term, gap-free stratospheric species profile data sets based on satellite occultation measurements and TOMCAT 3-D model
Authors: Dhomse Sandip , Chipperfield Martyn
Published: February 2023

Monitoring the atmospheric concentrations of the reactive species in the stratosphere, including greenhouse gases (GHGs), is crucial in order to improve our understanding of their climate impact. Although progress has been made towards construction of long-term ozone profile data sets, limited long-term profile data are available for other species. Here, we merge TOMCAT chemical transport model (CTM) output and profile measurements from two solar occultation instruments, the HALogen Occultation Experiment (HALOE) and the Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS), to construct a long-term (1991-2021), gap-free stratospheric profile data set (hereafter TCOM). The Extreme Gradient Boosting (XGBoost) regression model is used to estimate the corrections needed to apply to the CTM profiles to bring them into line with the observations.We have already released data sets for two important greenhouse gases: methane and nitrous oxide. For methane (TCOM-CH4), we use both HALOE and ACE satellite profile measurements (1992-2018) to train the XGBoost model and profiles from three later years (2019-2021) are used as an independent evaluation data set. As there are no nitrous oxide profile measurements for the earlier years, XGBoost-derived correction terms for TCOM-N2O profiles are derived using only ACE-FTS profiles for 2004-2018 time period with profiles from 2019-2021 again being used for the evaluation.Overall, both TCOM-CH4 and TCOM-N2O profiles show excellent agreement with the available satellite measurement-based data sets. Biases in TCOM-CH4 and TCOM-N2O are less than 10% and 50% throughout the stratosphere, respectively. Daily zonal mean TCOM-CH4 and TCOM-N2O profile data sets on altitude (15--60~km) and pressure (300--0.1~hPa) are publicly available via https://doi.org/10.5281/zenodo.7293740 and https://doi.org/10.5281/zenodo.7293740, respectively.Our presentation will discuss the construction, performance and availability of the TCOM data sets. We aim to release data sets for ozone (TCOM-O3), hydrogen chloride (TCOM-HCl), hydrogen fluoride (TCOM-HF), water vapour (TCOM-H2O), nitric acid (TCOM-HNO3), nitric oxide (TCOM-NO) and nitrogen dioxide (TCOM-NO2) shortly.
Changing length scales of moisture transport — their isotopic imprint and implications for remote moisture dependence
Authors: Bailey Adriana , Singh Hansi , Nusbaumer Jesse , Casado Mathieu , Cauquoin Alexandre , Heyblom Kyle , Worden John
Published: February 2023

Isotope ratios in water vapor record evaporation (E) and precipitation (P) along moisture transport paths. At low latitudes, the path-integrated E-P signal is dominated by local E and P, providing an indicator of tropical water balance. In contrast, at high latitudes, E and P patterns upstream overwhelm local signals, reflecting the dependence on remote moisture sources. This dependence defines the length scales of moisture transport. In the zonal mean, moisture transport length scales can be represented visually in two dimensions by moist isentropic surfaces, along which poleward moisture transport occurs. These surfaces explain why Rayleigh distillation reasonably approximates meridional variations in high-latitude isotope ratios while also providing a physical basis for why polar isotope-temperature relationships are distinct in space and time.  Isotopically enabled GCM simulations and short-duration Antarctic ground-based observations both lend support for the isentropic view of moisture transport. They also suggest that this framework provides a simple means to predict changes in length scale in a warmer climate, assuming zonal-mean humidity changes follow Clausius-Clapeyron scaling. However, isotopic observations with the vertical resolution and temporal coverage necessary to easily evaluate recent and expected future variations in moist isentropic transport are lacking. Here, we consider two possible alternative methods for testing predictions about long-term moisture length-scale changes with isotopic observations. Using the two-decade-long AIRS satellite record, we consider the extent to which mid-free tropospheric hydrogen isotope ratios, normalized by humidity, can provide a measure of length scale in a total-column sense. Second, we ask to what extent moist isentropic transport is set by episodic events, such as warm conveyor belts, that can be observed by infrequent but high-vertical-resolution airborne isotopic measurements. We discuss the implications of enhanced transport efficiency, expected in a warmer future, for increasing length scales and strengthening hydrological dependencies between remote locations.
Laminated stalagmite - based mean annual temperature reconstruction for middle reaches of the Yangtze River during the past 1200 years
Authors: Hu Zunyu , Hu Chaoyong
Published: February 2023

Temperature changes in the middle reaches of the Yangtze River (MRYR) have affected more than one billion people. In contrast to the warming trend in the Northern Hemisphere (NH), there was a sustained cooling trend of mean annual temperatures in the MRYR from 1930s to 1980s. Due to long-term mean annual temperature record has so far been lacking in the MRYR, it remains unclear to what extent regional peculiarities reflect region-specific internal climate variability or differences in driving mechanisms. Here, we present a reconstruction of temperature variability over the MRYR for the period CE 800-1998 using a laminated stalagmite (HS4) from Heshang cave, Yichang region, China. Observations of Heshang cave suggest that the growth of HS4 stalagmite is mainly affected by the temperature because of the stability of dripping water composition. Based on a significant positive correlation between the growth rate and the observed temperature, we reconstructed the mean annual temperature (MAT) for Yichang region with an explained variance of 39.8%, the correlation in interdecadal scale (10-yr low pass) was significantly improved (r=0.86). The new MAT reconstruction shows an almost similar trend with existing low resolution mean annual temperature records from historical document, which confirms the credibility of the reconstruction. Four warm (800s-880s, 1260-1450s, 1650s-1800s, 1900s-1950s) and three cold (890s-1250s, 1460s-1640s, 1810s-1890s) period were identified in MAT record. Our reconstruction shows a significant cooling in the MRYR during the MCA period, which may differ from previous NH temperature records. We suggested that the unique temperature variation in the MRYR may be driven by El Niño-Southern Oscillation (ENSO), as there was a significant positive correlation between MAT record and ENSO over the past 1200 years on the multidecadal scale. When sea surface temperatures in the eastern Pacific rise, so do temperatures in the MRYR, and vice versa. Our study provided the longest mean annual temperature record in the MRYR, and we also highlight that ENSO may be related to the temperature variation of the East Asian monsoon region, which has generally been ignored in past studies.
High-resolution modeling of historical forest fires in the Canton of Bern
Authors: Shastri Renuka Prakash , Brönniman Stefan , steinfeld Daniel
Published: February 2023

Forest fires are considered an important hazard in forested areas and a serious threat to forest ecosystem and buildings. The combination of drought, high temperatures, and wind increases the risk of forest fires. To better understand the fundamental causes and consequences of fire, we need to study the historical fire regimes. In this study, the meteorological conditions were simulated with the WRF model (Weather Research and Forecasting; Skamarock et al. 2008) for three historical forest fires, in the Canton of Bern, Switzerland (La Neuveville, April 1893, Simmenflueh, August 1911, Kirchberg, April 1915). In terms of area, these are the largest fires in the canton of Bern in the Swiss fire database. The "Twentieth Century Reanalysis" version 3 (20CRv3, Slivinski et al. 2019) was used as a boundary condition. 20CRv3 has a spatial resolution of about 75 km and a temporal resolution of three hours. Using WRF version 4.1.2 20CRv3 has now been gradually downscaled to a resolution of 1x1 km^2. Simulations suggest that the soil had dried out in the previous week and soil moisture had reached low values on the day the fire broke out. High-resolution fire weather indices are also calculated. A lack of precipitation and high temperatures led to high forest fire index values and a high to very high risk of forest fires. References[1] Slivinski, L. C.et al. (2019), Towards a more reliable historical reanalysis: Improvements to theTwentieth Century Reanalysis system. , Q. J. Roy. Meteorol. Soc. 145, 2876-2908.[2] Pfister, L. , S. Brönnimann, M. Schwander , FA Isotta , P. Horton, and C. Rohr, (2020) StatisticalReconstruction of Daily Precipitation and Temperature Fields in Switzerland back to 1864, Clim.past 16, 663-678.[3] Skamarock, WC, et al. (2008) A Description of The Advanced Research WRF Version 3. NCARTechnical Note.[4] Van Wagner, C.E. (1987): Development and Structure of the Canadian Forest Fire Weather IndexSystem, Forestry Technical Report, Canadian Forestry Service Headquarters, Ottawa.
A new shear box apparatus for investigating distributed deformation at the termination of continental transform faults
Authors: Withers Megan , Cruden Alexander
Published: February 2023

Continental transform faults transition to a new plate boundary type when strike-slip, transpression or transtension are no longer the most efficient way to accommodate plate motion. In some instances, rather than the transform fault ‘transforming’ plate motion directly to its connecting plate boundary, the continental transform fault can become ‘misaligned’ with its connecting plate boundary. Where a plate boundary misalignment occurs, plate motion that was localised on the transform fault can become distributed over a broad, intervening transition zone between the two major plate boundary faults. In this study we use scaled analogue models to investigate the development of fault networks in regions of localised and distributed simple shear and the transition between the two. We use digital image correlation (DIC) to analyse the surface deformation of the analogue model experiment and present results as incremental shear strain maps of the surface of the analogue models.  The results are compared to natural examples of plate boundary transition zones (e.g., Alpine Fault, New Zealand; North Anatolian Fault, Turkey; San Andreas Fault, USA).  In our previous analogue model experiments, regions of localised and distributed simple shear have been generated in an analogue shear box using a four-way stretchable fabric to adjust the basal boundary conditions. These experiments were limited by the elasticity of the stretchable material, which cannot deform infinitely. Here we will present preliminary results from a new shear box apparatus that uses carbon fibre rods to adjust the basal boundary conditions. This new apparatus has been designed to minimise the boundary effects caused by the limitations of the four-way stretchable fabric in our previous experiments.
Permeability of Lanhelin granite through the brittle-ductile transition.
Authors: Meyer Gabriel , Violay Marie
Published: February 2023

With increasing depth, crustal rocks gradually transition in deformation type, from being brittle/cataclastic to being crystal plastic, as well as in deformation mode, from being localized (faults, shear zones) to being ductile (homogeneous flow). This transitional layer, commonly referred to as brittle-ductile transition (BDT) has recently become the focus of economic development with the advent of Superhot Rock geotherm Reservoirs (SHR). Superhot Rock geothermal projects (e.g., Japan Beyond-Brittle Project, Iceland Deep Drilling Project, and Newberry Volcano) seek to extract heat from geothermal reservoirs where water reaches a supercritical state (≥ 400 °C). These could multiply the power output of geothermal plants by a factor ten, a progress that is critical in the context of the climate crisis.However, SHR reservoirs are generally localized at the BDT in semibrittle rocks (rocks deforming through a mixture of brittle and crystal plastic processes) which hydraulic properties are poorly understood.Here, we report experiments conducted in TARGET, a newly designed gas-confining triaxial apparatus located at EPFL, CH. We deformed cylindrical cores of Lanhelin granite of dimension 40 x 20 mm at a confining pressure of 100 MPa and temperatures ranging from 200 to 800°C and a strain rate of 10-6 s-1. While deforming, sample permeability was recorded using the pore pressure oscillation method with an oscillation amplitude of 5 MPa and a period of 2400 s.Lanhelin granite transitions from being localized with the formation of a sample scale fracture to being ductile between 600 and 800°C. In the localized regime, samples have an ultimate strength of around 600 to 650 MPa. In this regime, permeability initially slightly decreases upon loading from its initial value of 10-20 m2 before increasing with continued deformation. Permeability eventually plateaus upon sample failure and remains constant with further deformation. In the localized regime, permeability increase never exceed 2x10-19 m2. In the ductile regime, sample strength is halved and, past the initial decrease upon loading, permeability increases monotically by more than an order of magnitude.We interpret these data has being the result of sample bulk controlling the sample permeability. In our localized experiments, the fracture never connected the ends of the rock core but would concentrate all of the strain after nucleation, limiting permeability improvement by micro-cracking in the bulk. In the ductile regime, since no localization occurs, bulk permeability of the rock would continuously improve with strain. These results bear important implications for the engineering of permeability in semibrittle reservoirs as well as for the understanding of hydrothermal circulation in the continental crust.
Morphodynamic evolution of paraglacial spit complexes on a tide-influenced Arctic fjord delta (Dicksonfjorden, Svalbard)
Authors: Choi Kyungsik , Kim Dohyeong , Jo Joohee , Sohn Seungyeon , Nam Seung-Il
Published: February 2023

Recent global warming triggered pronounced geomorphic changes such as coastal retreat and delta progradation along the coastlines of the Arctic regions. Coastal morphodynamics and associated sediment transport at the Arctic fjord head remain relatively unexplored due to the logistically limited accessibility to the field area, especially at short-term temporal scales. A repeat survey using an unmanned aerial vehicle (UAV)-assisted photogrammetry was conducted to quantify the annual morphodynamics of gravel spit complexes developed on the tidal delta plain of the deglaciated Dicksonfjorden, Svalbard of the Arctic. Results show that the spit morpho-dynamics vary in time and space with an overall downfjord increase in the growth and migration rate of the spits. The youngest spits elongated 22 m yr− 1 and migrated landward 4.3 m yr− 1 between 2015 and 2019, marking the most pronounced spit morphodynamics documented to date in the Svalbard fjord systems. The spit morphodynamics is driven primarily by longshore drift and, to a lesser degree, by overwash processes. Gravels constituting the spits originate from the unconsolidated debris-flow deposits of old alluvial fans, which locally retreat 0.5 m yr− 1. The growth of the spit complexes is also fed by snow meltwater discharge on the alluvial fans, accounting for a downfjord imbrication of angular gravel layers that are intercalated with interlaminated sands and muds on the landward sides of the spits. The breached spits at the most upfjord location have remained stationary during the study period and presumably since the 1930s. Rapid delta progradation combined with an isostatic rebound after the Little Ice Age (LIA) has decreased spit morphodynamics on the tidal delta plain upfjord in Dicksonfjorden with infrequent and insignificant wave influence. The sparse distribution of the isolated spits signifies the intermittent spit development, which is constrained by the proximity to the protruded alluvial fans. The spit complexes in Dicksonfjorden highlight that climate change accelerates coastal geomorphic changes at the fjord head by enhancing wave intensity and regulating episodic sediment delivery that led to the downfjord shift in the locus of wave shoaling.
The role of sub-peatland critical zone structure on the hydrology of northern peatlands
Authors: Slater Lee , Comas Xavier , Reeve Andrew , Moore Henry , Niedzinski Victoria
Published: February 2023

The hydrology of northern peatlands is increasingly recognized to be influenced by groundwater flow between peat and underlying mineral sediments. These hydrologic fluxes have been measured in peatlands of central and northern Maine where peatlands formed in depressions within the complex landscape left after the last glacial ice retreat. Although most of these peatlands formed on top of a low permeability confining glaciomarine clay, surface digital elevation maps and subsurface geophysical datasets (ground penetrating radar, electromagnetic and resistivity imaging) indicate that, in places, they are often in hydrogeological contact with eskers (glacial outwash deposits) and possibly even directly in contact with bedrock. Hydrogeological datasets, including direct hydraulic head observations and indirect observations of seepage fluxes, support the case that these points of hydrogeological contact exert a profound influence on the surface hydrology, including pool formation, and ecology of these peatland systems. The unique properties of peat, including the formation of pipe structures, result in highly focused discharges of mineralized water as evidenced from temperature sensing and aqueous geochemistry data (specific conductance, dissolved iron, dissolved manganese). These pipe networks may exert a control on carbon cycling in peatlands via the delivery of nutrients, or possibly by serving as conduits for the release of free phase gas stored in the deep peat. Preliminary observations using gas traps lend support to this hypothesis.
The 2006 Pingtung intraslab earthquake doublet offshore southwestern Taiwan: Complex normal and strike-slip faulting in the northern Manila subduction zone where the continent-oceanic transitional slab subducts
Authors: Hu Wan-Lin , Wei Shengji , Feng Lujia , Hsiao Shih-Han , Ching Kuo-En , Hu Jyr-Ching
Published: February 2023

While intraslab events in subducting oceanic slabs have been widely studied, intraslab earthquakes in slabs of continent-oceanic transition zones, where lithospheric rheology differs, remain little understood. Here, we investigate the 2006 Pingtung (southwestern Taiwan) offshore intraslab earthquake doublet (Mw 7.0 and Mw 6.9), striking around the northern Manila subduction zone, where the highly thinned continental crust subducts. The two main shocks were at the depth of ~40 – 60 km, below the local MOHO, and ~8 minutes apart. The several source models that have been proposed vary, and do not consider all available observations. In this study, we incorporate comprehensive datasets, including teleseismic body waves, regional broadband, near-field strong motion waveforms, and high-rate GNSS, to propose a new source model, and further discuss source characteristics in the regional tectonic context. We first determine a reliable near-field velocity model and the frequency ranges for waveform inversions by path calibration based on inverting a nearby Mw 5.6 aftershock. We then constrain the multiple point sources (MPS) solutions for both events. The location and fault planes from MPS are used to resolve slip distributions by finite fault inversions. We finally validate this slip model by the static coseismic displacement observed by the dense, near-field campaign GNSS and precise leveling. Our results show that the Mw 7.0 normal event ruptured a west-dipping fault at the depth of ~40 km, characterized by at least two major asperities. This rupture was followed by the deeper Mw 6.9 strike-slip event, located ~40 km to the north. The earthquake sequence was located around a failed rift indicated by seismic tomography and likely represented a reactivation of the faults formed in the mantle lithosphere during the continental rifting in the northern South China Sea margin. The doublet’s complex mechanisms could be explained by stress fields imposed by the subducting transitional crust.
Relationship between synoptic weather pattern and surface Particulate Matter (PM) during winter and spring seasons over South Korea
Authors: Lee Dasom , Kim Hyun Cheol , Kim Kwanchul , Yun Sung Bum , Yang Jae-Hoon , Kim Dae-Hwan
Published: February 2023

Regional air quality over East Asia, including South Korea, has been a center of public attention recently because of a few episodes in which very high particulate matter (PM) concentrations have been observed. Predicting PM variation with lead time of a few hours up to days is one of the key areas that the governments are working on because it can benefit from early warning system to short-term mitigation effort. In this study, the influence of synoptic weather conditions on regional air quality was investigated with the occurrence frequencies of PM episodes as a function of various synoptic weather patterns during winter and spring. (1) During winter, dry moderate (DM) types occur frequently alongside high PM cases (24-h mean PM10 concentration > ). The composite weather map showed a weak northwesterly wind field as a potential cause. On the contrary, it is interesting to note that dry polar (DP) types can be associated with low PM cases (24-h mean PM10 concentration < ) as well as high PM depending on near-surface wind speed. (2) Furthermore, during spring, DM and dry tropical (DT) types were found to be highly correlated with high (much higher) PM concentrations, likely because of the enhanced static stability in the lower troposphere. It should be noted that PM concentration depends on the lower atmospheric stability. The close relationship between synoptic weather patterns and PM concentration suggests that synoptic weather can play an important role in regional air quality.
The underappreciated importance of solar radiation in constraining spring phenology of temperate ecosystems in the Northern and Eastern United States
Authors: Gu Yating , Zhao Yingyi , Guo Zhengfei , Meng Lin , Zhang Kun , Wang Jing , Lee Calvin K.F. , Xie Jing , Wang Yantian , Yan Zhengbing , Zhang He , Wu Jin
Published: February 2023

Spring phenology of temperate ecosystems displays high sensitivity to the recent climate change, and has generated various impacts on plant growth, biotic interactions, ecosystem productivity, and local environmental conditions. Although various prognostic models relying on environmental variables, mainly including temperature and photoperiod, have been developed for spring phenology, comprehensive ecosystem-scale evaluations over large geographical extents and long-time periods remain lacking.  Further, environmental variables other than temperature and photoperiod might also importantly constrain spring phenology modelling but remain under-investigation. To address these issues, we leveraged 20-years datasets of environmental variables (Daymet) and the spring phenology metric (i.e., the greenup date) respectively derived from MODIS and PhenoCams across 108 sites in the Northern and Eastern United States. We firstly cross-compared MODIS-derived greenup date with PhenoCams with high accuracy (R2=0.75). Then, we evaluated the three prognostic models (e.g., Growing Degree Date (GDD), Sequential (SEQ) and optimality-based (OPT)) with MODIS-derived spring phenology, assessed the model residuals and their associations with soil moisture, rainfall, and solar radiation, and improved and re-evaluated the models by including the variable contributing to high model residuals. We found that 1) all models demonstrated good capability in characterizing spring phenology, with OPT performing the best (RMSE=8.04±5.05 days), followed by SEQ (RMSE=10.57±7.77 days) and GDD (RMSE=10.84±8.42 days), 2) all models displayed high model residuals showing tight correlation with solar radiation (r=0.45-0.75), and 3) the revised models that included solar radiation significantly performed better with an RMSE reduction by 22.08%. Such results are likely because solar radiation better constrains early growing season plant photosynthesis than photoperiod, supporting the hypothesis of spring phenology as an adaptive strategy to maximize photosynthetic carbon gain (approximated by solar radiation) while minimizing frost damage risk (captured by temperature). Collectively, our study reveals the underappreciated importance of solar radiation in constraining spring phenology of temperate ecosystems, and suggests ways to improve spring phenology modelling and other phenology-related ecological processes.
Observed subdaily variations in air–sea turbulent heat fluxes under different marine atmospheric boundary layer stability conditions in the Gulf Steam
Authors: Song Xiangzhou , Xie Xuehan , Yan Yunwei , Xie Shang-Ping
Published: February 2023

Based on data collected from 14 air–sea buoys in the Gulf Stream, this study presents an examination of how the hourly air–sea turbulent heat fluxes vary on subdaily timescales under persistent marine atmospheric boundary layer (MABL) stability conditions. The annual mean magnitudes of the subdaily variations in the latent heat (LH) and sensible heat (SH) at all stations are determined to be 40 and 15 Wm-2, respectively. Under near-neutral conditions, the hourly anomalies of the air–sea humidity and temperature differences are the major drivers of the subdaily variations in LH and SH, respectively, followed by nonlinear effects and wind anomalies. Wind anomalies play dominant roles in determining the subdaily variations in LH and SH when the MABL is stable. In contrast, the contributions of the hourly anomalies of the air–sea differences in humidity and temperature are secondary but also significant. For a convectively unstable MABL, the wind anomalies control the subdaily variations in LH, whereas the subdaily variations in SH are dominated by the air–sea temperature anomalies. Accordingly, the above mechanism also controls the subdaily magnitudes. Quantitative estimates of the above relations are given in this study. However, compared to the observations when using daily mean SST, the subdaily variations in the reanalysis are found to be underestimated on average by 17% and 5% for LH and SH, respectively. Resolving the subdaily variations contributes significantly to the mean LH/SH estimates. For near-neutral and unstable MABLs, the subdaily contributions are O(100) and O(20) Wm-2 for LH and SH, respectively, while they are O(10) Wm-2 for LH/SH under stable conditions.
A millennial-scale tephra event-stratigraphic record of the South China Sea since the penultimate interglacial
Authors: Kong Deming , Feng Weijia , Yang jiawen , Bao Chuang , Chen Min-Te
Published: February 2023

Large volcanic eruptions have significant impacts on climate and environmental changes. The deposition of tephra in marine sediments may serve as an eruption recorder, but it has not been extensively studied in the western Pacific. This study explored a millennial-scale tephra event-stratigraphy with multiple indicators in a sediment core collected from the eastern South China Sea (SCS) basin. The magnetic susceptibility (MS), Fe and Mn concentration determined by X-ray fluorescence (XRF), and identification of individual ash particles were used to identify tephra layers and reconstruct the history of volcanic activity. Nine visible volcaniclastic units (VVU) and two cryptotephra layers have been identified based on their distinct features, as manifested by high MS, Fe, and Mn concentrations, and single-peak grain size distribution. The VVUs and cryptotephra layers reveal elevated volcanic activities. Using the radiocarbon age model and oxygen isotope stratigraphy, these episodes could roughly correspond to the following periods: 1-11 ka, 16-17 ka, 27-31 ka, 41-42 ka, 45-46 ka, 49-50 ka, 77-80 ka, 90-91 ka, 97-99 ka, 116-126 ka, and 132-140 ka. The alkenone-derived SST has significant glacial cycles and good synchronicity with other SCS SST records, which could partially help build the preliminary age model. Despite possible age errors larger than 1 kyr, the discovery and timing of tephra layers provide a preliminary framework to further investigate the impact of historical volcanic eruptions on climate changes.
Effects of land uses and rainfall regimes on surface runoff andsediment yield in a nested watershed of the Loess Plateau, China
Authors: Zhao Jiongchang , Zhang Jianjun , Yu Yang
Published: February 2023

Land-use and rainfall characteristics are two crucial influencing factors that affect the surface runoff and soil loss process; however, less attention has been paid to nested watersheds in vulnerable geo-ecosystems. In this study, we analyzed rainfall characteristics impacts on runoff and sediment in one of the nested watersheds, which contains six sub-watersheds with different land uses (secondary forest watershed, mixed forest watershed, closed watershed, plantation watershed, farmland watershed and farming-pastoral watershed) on the Loess Plateau, China. According to rainfall amount, rainfall duration and maximum rainfall intensity within 30 min (I30), 180 rainfall events during 2004–2019 were categorized into four types using K-means clustering method, and different hydrological years were distinguished. The runoff coefficient and sediment yield under the rainfall regime I (little precipitation, moderate duration of precipitation, low intensity of precipitation) were the lowest; under the rainfall regime IV (high precipitation, short duration of precipitation, high intensity of precipitation), these values were the largest. The average runoff coefficient among the six sub-watersheds analyzed varied as follows: farmland watershed (2.42%) > farming-pastoral watershed (2.38%) > closed watershed (1.11%) > secondary forest watershed (1.08%) > mixed forest watershed (0.73%) > plantation watershed (0.43%). The closed watershed had the lowest average sediment yield, while the farming-pastoral watershed showed the highest one. In addition, the runoff coefficient and sediment yield also changed differently in various hydrological years. The results of this study suggest that natural restoration measures are the optimal choice for coordinating the relationship between surface runoff and sediment yield. In future research, enhanced long-term monitoring is needed to accurately describe watershed processes. 
Afforestation with Caragana korshinskii enhances the quantity and stability of soil organic carbon in the northern Loess Plateau, China
Authors: Li Yangyang , Chi Tianqi , Zhang Xiaoping
Published: February 2023

The northern Loess Plateau, China is an eco-environment fragile zone with the most serious soil and water loss in the world. Hence, soil face the direct threat of texture coarsening, fertility decline and loss of microbial biodiversity, etc. Selecting rational afforestation species will be beneficial for the maintenance and improvement of soil structure and function in this area. Populus simoni (PS, tree), Caragana korshinskii (CK, shrub) and Salix psammophila (SP, shrub) are major perennial woody plants for afforestation in this region, although they play important roles in preventing soil and water loss, blocking wind and fixing sand and increasing farmers’ income, it is not clear how long-term plantation of these plants affect the quantity and stability of soil organic carbon (SOC) and whether the afforestation species are sustainable for soil resources. So, mature stands over 30 years per species were chosen, and SOC and its stability (the intra-microaggregate fine particulate OC and mineral-associated OC are protected C) whthin 0-10 cm and 10-20 cm were compared. Wet sieving method was used to separate water-stable aggregates, and physicochemcial methods were used to isolate different organic carbon fractions. The results indicated that: 1) SOC content of the bulk soil for CK stands increased by 46.4% and 75.8%, respectively at 0-10 cm, and 32.6% and 67.5%, respectively at 10-20 cm compared to PS and SP stands. 2) The <0.25 mm microaggregate content accounted for more than 74% for three stands, and CK stands had higher free microaggregate (0.053-0.25 mm) during both depths and higher small macroaggregate (0.25-2 mm) at 0-10 cm compared to PS and SP stands, the mean weight diameter at the 0-10 and 10-20 cm soil for CK stands were significantly increased compared with PS and SP treatments. 3) The protected C accounted for 74% ~85% of the total SOC. The protected carbon was significantly and positively correlated with the SOC across treatments. In conclusion, long-term C. korshinskii planation can increase the quantity and stability of SOC via increasing the content of protected C, suggesting C. korshinskii is the rational afforestation species to combat soil degradation under future climate change from the angle of C sequestration. 
Changes in global evaporation for the past four decades identified by the complementary evaporation principle and the Budyko framework
Authors: Kim Daeha , Chun Jong Ahn
Published: February 2023

The complementary evaporation principle (CEP) could well explain the past changes in global evaporation while avoiding uncertainties in precipitation and soil data. However, it is still difficult to estimate the Priestley-Taylor coefficient (α) for the wet-surface evaporation without actual evaporation data. Here, we proposed an empirical approach that links the CEP and a traditional Budyko equation in order to determine α in locations where no actual evaporation (E) data are available. The CEP–Budyko combined framework enabled us to local climate conditions in α, producing more plausible E estimates in the ungauged locations. We also assessed latitudinal and temporal variations of the E estimates for the past 40 years. This study highlights that the optimal α for CEP is unlikely constant in space, since it needs to be conditioned by local climates.
Assessing volcanism during the PETM based on mercury isotope and abundance data
Authors: Jin Simin , Kemp David , Yin Runsheng , Sun Ruiyang , Shen Jun , Jolley David , Vieira Manuel , Huang Chunju
Published: February 2023

The Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma) was an abrupt hyperthermal event that has been linked to carbon release from volcanism associated with the North Atlantic Igneous Province (NAIP). Anomalously high sedimentary mercury (Hg) concentrations, a proxy for volcanism, have been recorded across the PETM from some locations, supporting this link. Nevertheless, Hg concentration data alone offer little insight into emplacement mechanisms and carbon source(s), and can be influenced by depositional conditions and post-depositional alteration. To help address this issue, and more critically evaluate the efficacy of Hg as a volcanism proxy, Hg-isotope data have been obtained across a thick, deep-marine sedimentary record of the PETM from the North Sea that was deposited in close proximity to active NAIP volcanism. These data are combined with a new global compilation of Hg concertation data across the PETM, which includes new Hg concentration data obtained from five globally distributed sites. Analysis of all the data demonstrates extensive and at least intercontinental Hg enrichments during the onset of the PETM carbon-isotope excursion, and that this was related to a major transient pulse of extrusive volcanism. Hg-isotope data support protracted volcanism through the PETM, but the evidence for sustained Hg enrichment from volcanism through the entirety of the PETM is equivocal. Towards the end of, and after, the PETM, the data suggest an overall waning influence of volcanogenic Hg.