bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi-method dating of ancient permafrost of the Batagay megaslump, East Siberia
Authors: Wetterich Sebastian , Murton Julian B. , Toms Phillip , Wood Jamie , Blinov Alexander , Opel Thomas , Fuchs Margret C. , Merchel Silke , Rugel Georg , Gärtner Andreas , Savvinov Grigoriy
Published: March 2020

Dating of ancient permafrost is essential for understanding permafrost stability and interpreting past climate and environmental conditions over Pleistocene timescales but faces substantial challenges to geochronology.

Here, we date permafrost from the world’s largest retrogressive thaw slump at Batagay in the Yana Upland, East Siberia (67.58 °N, 134.77 °E). The slump headwall exposes four generations of ice and sand-ice (composite) wedges that formed synchronously with permafrost aggradation. The stratigraphy differentiates into a Lower Ice Complex (IC) overlain by a Lower Sand Unit, an Upper IC and an Upper Sand Unit. Two woody beds below and above the Lower Sand Unit represent the remains of two episodes of taiga forest development prior to the Holocene forest. Thus, the ancient permafrost at Batagay potentially provides one of the longest terrestrial records of Pleistocene environments in western Beringia.

We apply four dating methods to the permafrost deposits to disentangle the chronology of the Batagay permafrost archive – optically-stimulated luminescence (OSL) dating of quartz and post-infrared-stimulated luminescence (pIR-IRSL) dating of feldspar as well as accelerator mass spectrometry-based Cl-36/Cl dating of wedge ice and radiocarbon dating of organic material.

The age information obtained so far indicates that the Batagay permafrost sequence is discontinuous and that the Lower IC developed well before MIS 7, the overlying Lower Sand Unit formed during MIS 6, and the Upper IC and the Upper Sand Unit formed both during MIS 3-2.

Additional sampling for all dating approaches presented here took place in spring 2019, and is part of ongoing research to enhance the geochronology of the exceptional palaeoenvironmental archive of the Batagay megaslump.
Development of convection in a mesoscale cloud system and its effect on the microphysics over the tropical Atlantic Ocean
Authors: Cui Zhiqiang , Blyth Alan , Abel Steven , Barrett Paul , Gordon Hamish
Published: March 2020

Climate models have large uncertainty to represent the low clouds in the transitional zone from stratocumulus to cumulus clouds. This talk presents an observational study of a mesoscale cloud system near Ascension Island during the CLouds and Aerosol Radiative Impacts and Forcing (CLARIFY) field campaign. Extensive aircraft measurements were made to investigate the cloud microphysics when convection developed in a stratiform cloud system. The aircraft penetrated the clouds at levels below, within, and above the main layer. In-cloud penetrations show that the development of convections increased the drop number concentration, the effective radius of drops, the size of drizzle drops, and liquid water content. In the process of convection development, the morphology of the cloud changed from an overcast stratocumulus system to organised convective clouds. The wind shear and the compensating subsidence associated with the convections seemed to be responsible for the appearance of the system. The results indicate that the convective clouds significantly affected the stratocumulus cloud properties in the transition. Our study of the microphysical processes in the transitional zone helps to improve the representation and evolution of low clouds in models. 

 
Efficient multi-GNSS processing based on raw observations from large global station networks
Authors: Strasser Sebastian , Mayer-Gürr Torsten
Published: March 2020

The year 2020 is going to mark the first time of four global navigation satellite systems (i.e., GPS, GLONASS, Galileo, and BeiDou) in full operational capability. Utilizing the various available observation types together in global multi-GNSS processing offers new opportunities, but also poses many challenges. The raw observation approach facilitates the incorporation of any undifferenced and uncombined code and phase observation on any frequency into a combined least squares adjustment. Due to the increased number of observation equations and unknown parameters, using raw observations directly is more computationally demanding than using, for example, ionosphere-free double-differenced observations. This is especially relevant for our contribution to the third reprocessing campaign of the International GNSS Service, where we process observations from up to 800 stations per day to three GNSS constellations at a 30-second sampling. For a single day, this results in more than 200 million raw observations, from which we estimate almost 5 million parameters.

Processing such a large number of raw observations together is computationally challenging and requires a highly optimized processing chain. In this contribution, we detail the key steps that make such a processing feasible in the context of a distributed computing environment (i.e., large computer clusters). Some of these steps are the efficient setup of observation equations, a suitable normal equation structure, a sophisticated integer ambiguity resolution scheme, automatic outlier downweighting based on variance component estimation, and considerations regarding the estimability of certain parameter groups.
Equatorial deep jets and their influence on the equatorial mean circulation in an idealised model forced by intraseasonal momentum flux convergence
Authors: Bastin Swantje , Claus Martin , Brandt Peter , Greatbatch Richard J.
Published: March 2020

Equatorial deep jets (EDJ) are vertically stacked, downward propagating zonal jets that alternate in direction with depth. In the tropical Atlantic, they have been shown to influence both surface conditions and tracer variability. Despite their importance, the EDJ are absent in most ocean models, most likely due to a lack of vertical resolution. However, when the vertical resolution is sufficiently high, EDJ oscillating at a period of about 4.5 years are present in idealised model configurations driven by steady wind forcing. We have used such a model for a basin-wide reconstruction of the intraseasonal eddy momentum flux convergence, which has recently been shown to be a large contributor to the EDJ maintenance (Greatbatch et al., 2018). When we apply the diagnosed momentum flux convergence that is oscillating at the EDJ period as forcing in a model without wind forcing, EDJ develop, allowing us to verify the mechanism proposed in Greatbatch et al. (2018). Additionally, we can isolate the nonlinear effect that the EDJ have on the time mean zonal flow at intermediate depths. We can show that the EDJ drive time mean zonal flow that is similar in structure to the mean flow measured by Argo floats at 1000 m depth, contributing (in our idealised setup) about one fifth of the total magnitude of the observed flow, the rest likely resulting from direct forcing by downward propagating intraseasonal waves as shown before in other studies.

 

References:

Greatbatch, R. J., M. Claus, P. Brandt, J.-D. Matthießen, F. P. Tuchen, F. Ascani, M. Dengler, J. Toole, C. Roth, J. T. Farrar, 2018: Evidence for the Maintenance of Slowly Varying Equatorial Currents by Intraseasonal Variability. Geophysical Research Letters, 45, 1923-1929.
Stable isotope data of modern and ancient microbialites
Authors: Rodler Alexandra S. , Bruggmann Sylvie , Goderis Steven , Claeys Philippe
Published: March 2020

Carbonate-based reconstructions of environmental conditions in the Precambrian rely heavily on shallow-water and typically microbially-mediated carbonates. This is because Precambrian carbonate rocks formed either microbially or abiotically. Consequently, organo-sedimentary carbonate structures (microbialites) are extensively used as archives of physico-chemical conditions of early Earth environments using traditional isotopes such as stable carbon and oxygen isotopes. When post-depositional alteration is carefully evaluated, valuable information on local seawater chemistry may be gained. More recently, non-traditional isotope systems are applied to microbialites for reconstructing, for example, the redox evolution of our planet. However, interpretations of non-traditional isotope data are challenging, and information on diagenetic alteration is crucial. We present geochemical analyses of modern and ancient microbialites, which are part of an ongoing study on the chromium isotope systematics in modern and fossil microbialites (1). Here, we focus on stable C- and O-isotope data and diagenetic alteration of the analysed microbialites. This approach aims to build a framework for interpreting paleo-environmental reconstructions using non-traditional isotope systems. First results of powdered sub-samples of the modern microbialites show that stable C- and O-isotope data reliably reflect the environmental conditions of their depositional setting: high δ13C values (+2 to +8 ‰) indicate extensive microbial activity and high δ18O values point to evaporative settings. One set of Precambrian microbialite samples also has high δ13C values (~+4 ‰), similar to the modern microbialites, but in comparison to modern samples, relatively low δ18O values (~-3 ‰). Yet, another set of Precambrian microbialite samples display both low δ13C (~-0.5 ‰) and δ18O values (-3 to -6 ‰). The results are interpreted to indicate a different depositional environment and/or more likely, a stronger degree of post-depositional diagenetic alteration that might also explain the comparatively low δ53Cr values of these samples.
Catchment scale prediction of soil moisture trends from Cosmic Ray Neutron Rover Surveys using machine learning
Authors: Nixdorf Erik , Hannemann Marco , Ködel Uta , Schrön Martin , Kalbacher Thomas
Published: March 2020

Soil moisture is a critical hydrological component for determining hydrological state conditions and a crucial variable in controlling land-atmosphere interaction including evapotranspiration, infiltration and groundwater recharge.

At the catchment scale, spatial- temporal variations of soil moisture distribution are highly variable due to the influence of various factors such as soil heterogeneity, climate conditions, vegetation and geomorphology. Among the various existing soil moisture monitoring techniques, the application of vehicle-mounted Cosmic Ray Sensors (CRNS) allows monitoring soil moisture noninvasively by surveying larger regions within a reasonable time. However, measured data and their corresponding footprints are often allocated along the existing road network leaving inaccessible parts of a catchment unobserved and surveying larger areas in short intervals is often hindered by limited manpower.

In this study, data from more than 200 000 CRNS rover readings measured over different regions of Germany within the last 4 years have been employed to characterize the trends of soil moisture distribution in the 209 km2 large Mueglitz River Basin in Eastern Germany. Subsets of the data have been used to train three different supervised machine learning algorithms (multiple linear regression, random forest and artificial neural network) based on 85 independent relevant dynamic and stationary features derived from public databases.  The Random Forest model outperforms the other models (R2= ~0.8), relying on day-of-year, altitude, air temperature, humidity, soil organic carbon content and soil temperature as the five most influencing predictors.

After test and training the models, CRNS records for each day of the last decade are predicted on a 250 × 250 m grid of Mueglitz River Basin using the same type of features. Derived CRNS record distributions are compared with both, spatial soil moisture estimates from a hydrological model and point estimates from a sensor network operated during spring 2019. After variable standardization, preliminary results show that the applied Random Forest model is able to resemble the spatio-temporal trends estimated by the hydrological model and the point measurements. These findings demonstrate that training machine learning models on domain-unspecific large datasets of CRNS records using spatial-temporally available predictors has the potential to fill measurement gaps and to improve soil moisture dynamics predictions on a catchment scale.
Late 20th century increase in northern Svalbard glacier-derived runoff tracked by encrusting coralline algae
Authors: Hetzinger Steffen , Halfar Jochen , Zajacz Zoltan , Möller Marco , Wisshak Max
Published: March 2020

The Arctic cryosphere is changing at a rapid pace due to global warming and the large-scale changes observed in the Arctic during the past decades exert a strong influence throughout the global climate system. The warming of Arctic surface air temperatures is more than twice as large as the global average over the last two decades and recent events indicate new extremes in the Arctic climate system, e.g. for the last five years Arctic annual surface air temperature exceeded that of any year since 1900 AD. Northern Spitsbergen, Svalbard, located in the High Arctic at 80°N, is a warming hotspot with an observed temperature rise of ~6°C over the last three decades indicating major global warming impacts. However, even the longest available datasets on Svalbard climatic conditions do not extend beyond the 1950s, inhibiting the study of long-term natural variability before anthropogenic influence. Ongoing climate trends strongly affect the state of both glaciers and seasonal snow in Svalbard. Modeled data suggest a marked increase in glacier runoff during recent decades in northern Svalbard. However, observational data are sparse and short and the potential effects on the surface ocean are unclear.
This study focuses on the ultra-high-resolution analysis of calcified coralline algal buildups growing attached to the shallow seafloor along Arctic coastlines. Analysis of these new annually-layered climate archives is based on the long-lived encrusting coralline algae Clathromorphum compactum, providing a historic perspective on recently observed changes. Here, we present a 200-year record of past surface ocean variability from Mosselbukta, Spitsbergen, northern Svalbard. By using algal Ba/Ca ratios as a proxy for past glacier-derived meltwater input, we investigate past multi-decadal-scale fluctuations in land-based freshwater contributions to the ocean surface layer. Our records, based on multiple coralline algal specimens, show a strong and statistically significant increasing trend in algal Ba/Ca ratios from the 1990s onwards, suggesting a drastic increase in land-based runoff at Mosselbukta. The drastic rate of increase is unprecedented during the last two centuries, directly capturing the impact of amplified surface air temperature warming on coastal high Arctic surface ocean environments.

 
Joint inversion and collaborative interpretations in complex geodynamical context
Authors: Tiberi Christel , Clutier Adeline , Plasman Matthieu , Gautier Stéphanie , Parat Fleurice , Lopez Marie
Published: March 2020

Active regions concentrate different geodynamical processes sometimes with complex interactions and retroactions. In order to understand the associated lithospheric deformation and evolution, scientists deduce crustal and mantle structures from sparse, inaccurate and indirect observations. In particular, geophysics aims at retrieving physical properties of crustal or lithospheric media from gravity, electric or seismic measurements. Those indirect tools have been used for decades now to image the Earth Interior at many different scales, from the surface down to the Core.

Besides, density, resistivity or seismic velocity retrieved from geophysical inversions are sensitive to many different factors (temperature, pressure, melt, composition…), each of them impacting the parameters variously. Finally, each of these methods presents its own depth investigation and accuracy, which depends on time lap, network configuration, data wavelength, etc.

In order to distinguish the role of each factor in the lithospheric structure heterogeneity, and to counteract the different method limits, geophysicists have combined their observations in combined schemes for decades now. We will present here how jointly inverting seismic tomography and gravity may help to better understand complex zones implying melt, faults, crustal modification and plate interaction. When mathematical link between the parameters doesn’t exist, we will present a combination of petrophysics and geophysics, that brings new information on past and present dynamical evolution in a magmatic area (East African Rift, Tanzania). Finally, we will address the question of the real benefit of a joint inversion, and whether we can combine all kind of data.
Dust Interaction with Energetic Particles — A Laboratory Simulation
Authors: Pavlů Jiří , Nouzák Libor , Wild Jan , Vaverka Jakub , Richterova Ivana , Šafránková Jana , Němeček Zdeněk
Published: March 2020

Dust grains in space frequently face energetic particles, e.g., ions, electrons, X-ray, positrons, etc. Such a broad variety of particle–dust interactions plays a significant role in dust charging and surface modification. The combination of high energy of particles together with a limited size of objects (dust) comprises interesting mesoscopic structure with non-obvious behavior. While in situ experiments are difficult and rare, we observed particular interactions experimentally in an electrodynamic trap. It allows us to study of a single dust grain temporal evolution under well defined conditions, i.e., to somewhat separate aforementioned processes and to investigate them individually. We present a summary of laboratory simulations and their
comparison with simple theoretical models. We discuss dust charging by different elementary particles and its importance for various space regions.
Receiver function analysis for determining the crustal structure of Tenerife (Canary Islands, Spain)
Authors: Ortega Víctor , D'Auria Luca
Published: March 2020

The receiver function analysis (RF) is a commonly used and well-established method to investigate subsurface crustal and upper mantle structures, removing the source, ray-path and instrument signatures. RF gives the unique signature of sharp seismic discontinuities and information about P-wave (P) and shear-wave (Ps) velocity below the seismic station. In particular using the direct P-wave as a known reference arrival time, and the relative arrival time of P-to-S (Ps) conversions as well as PpPs, PsPs and PsSs reflections allow constraining the principal crustal structures and allows us to study the effects of dipping interfaces and crustal layering.

The aim of this work is to use the RF non-conventional analysis to study the crustal structures of Tenerife. Previous studies on receiver functions analysis an active oceanic volcanic island, showed that the Moho topography have a high dipping under the volcanic edifice and a depth ranging between 11 and 18 km depth. Furthermore, it has been observed that some phases related with a layer of volcanic rocks having a thickness of about 5.5 km and a P-wave velocity (Vp) of approximately 6 Km/s, lies above an old oceanic crust having a thickness of about 7 km and a Vp of about 6.8 km/s.

For this study we applied both time and frequency domain deconvolution to obtain receiver functions. The determination of the average crustal thickness and has been achieved by using the commonly uses H-k method. To constrain the internal crustal layering, we used a non-linear inversion algorithm based on full waveform modeling of the receiver function. Finally, we realized a modelling of the reflected and converted phases in the crust using seismic ray tracing. Our modelling takes into account the surface topography as well as an arbitrary geometry of the Moho.

In conclusion our results showed the presence of a thick layer (up to 5.5 km) of volcanic rocks in the central part of the island overlying an oceanic crust whose total thickness varied from 18 km in the central part to about 11 km in the peripheral areas. This work represents the first step toward further studies devoted at a finer imaging of the crustal structures of Tenerife using receiver function analysis.
Reactive bromine chemistry in the Rann of Kachchh salt desert
Authors: Kuhn Jonas , Kumar Vinod , Wagner Thomas , Warnach Simon , Platt Ulrich
Published: March 2020

The Rann of Kachchh is a salt desert in the southern border area of India and Pakistan. Recently, high amounts of bromine monoxide (BrO) were observed there in satellite measurements of the Ozone Monitoring Instrument (OMI). Release mechanisms of reactive bromine, dominating chemical processes, the influence of the ambient atmosphere and transport processes, etc. are not well understood in general. Furthermore, due to their short time scales these processes are difficult to assess with satellite instruments, which only offer a single measurement per day with limited spatial resolution.

Here, we present BrO, HCHO and nitrogen dioxide (NO2) measurements from ground-based MAX DOAS performed at two different locations in the Rann of Kachchh salt desert in Gujarat, India during three weeks in March and April 2019. We observe large amounts of BrO building up during daytime reaching maxima of several tens of ppt in the late afternoon. Additional mobile measurements performed directly over the salt gave similar results to the measurements at 5-15 km distance from the salt surface, suggesting that the BrO formation time scale and effective life times during daytime are at least of the order of several minutes to a few hours. Additional in-situ ozone measurements indicate ozone depletion events linked to the episodes of high BrO abundance. This indicates that BrO is formed by bromine atoms reacting with ozone and then being recycled via BrO self-reaction and heterogeneous processes involving aerosol surfaces, as proposed for other environments (Polar Regions, volcanic plumes).

While we found high but steady HCHO levels, the observed NO2 levels showed a distinct anti-correlation to BrO, indicating coupling of bromine- and NOx-chemistry and thereby the influence of the pollution level of the ambient atmosphere. Formation of bromine nitrate probably delays the formation of large BrO amounts, but might also support the recycling of bromine atoms through heterogeneous chemistry.
Forestation effects on soil temperature across the European continent.
Authors: Sofiadis Giannis , Katragkou Eleni , Davin Edouard , Meier Ronny , Rechid Diana , Hoffmann Peter , Strada Susanna , Warrach-Sagi Kirsten , Jach Lisa , Soares Pedro , Lima Daniela , Cardoso Rita Margarida , Tolle Merja , Breil Marcus , Standberg Gustav
Published: March 2020

Land-Use and Land Cover Changes (LULCC) play a fundamental role in land-atmosphere interactions, since they mainly regulate the exchange of latent and sensible heat between the ground and the upper air, while they control the amount of shortwave radiation absorbed by the ground. In this study, we make an attempt to investigate the biogeophysical effects of extreme land cover changes on soil variables, such as soil temperature and soil moisture. In particular, we analyze a multi-model ensemble of nine different regional climate model simulations, which had been performed over the Euro-CORDEX domain in the frame of the WCRP CORDEX Flagship Pilot Study LUCAS (Land Use and Climate Across Scales). We compare two idealized experiments: a maximally forested (called FOREST) and a fully grassed Europe (called GRASS). According to our results, the soil temperature response to forestation varies among the climate models. They show a profound seasonality and dependence by latitude. In winter, the magnitude of soil temperature changes is considered weak, showing a warming in high latitudes (around +1oC on average) and a weak cooling over the Mediterranean region. During the summertime, in contrast, soil temperatures are higher in the GRASS experiment, especially in Central and Southern Europe (ranging from +1oC to +3oC depending to the model), underlying the essential role of soil moisture in determining the land-atmosphere feedbacks during the summer. In our contribution, we will present in detail the role of forest and grass characteristics and its effects on seasonal soil conditions across Europe[DR1] .  
The ASTER Volcano Archive (AVA): Twenty years of global monitoring of active volcanoes
Authors: Abrams Michael , Torres Alexander , Davies Ashley
Published: March 2020

Orbital remote sensing is the only tool allowing global, systematic monitoring of all 1500+ active volcanoes (based on the Smithsonian Holocene catalog). A specialized archive has been developed at the Jet Propulsion Laboratory: the ASTER Volcano Archive (AVA). AVA is comprised of over 200,000 ASTER frames spanning 20 years of the NASA’s Terra platform mission. The ASTER Volcano Archive (AVA: http://ava.jpl.nasa.gov) is the world's largest (at 100+Tb), and the only high spatial resolution (15-30-90m/pixel), multi-spectral (VNIR-SWIR-TIR), downloadable (kml enabled) dedicated archive of volcano imagery. The system is designed to facilitate parameter-based data mining, and for the implementation of archive-wide data analysis algorithms. Results include thermal anomaly detection and mapping, the temporal variability of individual volcanic emissions, as well as the detection of SO2 plumes from both explosive eruptions and from passive emissions. A major expansion of the archive was implemented with the ingest of the full 1972-present Landsat dataset. In addition, the archive includes NASA Earth Observing-1 (EO-1) multispectral and hyperspectral imagery (10-30 m/pixel) of a subset of the Holocene catalog volcanoes obtained between 2004 and 2017. The newest version of AVA has been ported to the Amazon Web Services cloud and managed by the Jet Propulsion Laboratory’s Hybrid Science Data System (HySDS). This migration provides all of the previous capabilities, providing a stable, fast platform for rapid access to data. The system is updated with new data daily, with a latency of a few days following data acquisition. Currently we are developing a new user interface to facilitate easy, fast and efficient access to the archive. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract to NASA. © 2020 Caltech.
Lubrication Dynamics for Exhumation of high-pressure Rocks in Subduction Zones
Authors: Maiti Giridas , Sen Joyjeet , Mandal Nibir
Published: March 2020

Subduction zones witness exhumation of deep crustal rocks metamorphosed under high pressure (HP) and ultra-high pressure (UHP) conditions, following burial to depths of 100 km or more. The exhumation dynamics of HP and UHP rocks still remains a lively issue of research in the Earth science community. We develop a new tectonic model based on the lubrication dynamics to show the exhumation mechanism of such deep crustal rocks in convergent tectonic settings. Our model suggests subducting plate motion produces a dynamic pressure in the subduction wedge, which supports the excess gravitational potential energy of the thicker and relatively denser overriding plate partly lying over the buoyant subduction wedge. A drop in the dynamic pressure causes the overriding plate to undergo gravitational collapse and forces the wedge materials to return to the surface. Using lubrication theory we estimate the magnitude of dynamic pressure (P) in the wedge as a function of subduction velocity (us), convergence angle (α) and wedge viscosity (µ). We also conduct thermo-mechanical numerical experiments to implement the lubrication model in subduction zones on a real scale. Our analysis suggests that drop in wedge dynamic pressure below a threshold value due to decease in us  and µ, or by other processes, such as slab rollback and trench retreat facilitate exhumation of deep crustal rocks. Finally we discuss their implications for the exhumation of deep crustal rocks in different subduction setups such as the Himalayan continental subduction, the Mediterranean realm (Calabria–Apennine and Aegean belts) and Western Alps.
Monte Carlo test-particle model of Mercury's ionized exosphere: Global structure and dynamics
Authors: Werner Anita Linnéa Elisabeth , Leblanc François , Chaufray Jean-Yves , Modolo Ronan
Published: March 2020

The Mercury plasma environment is enriched in heavy ions (mass-per-charge ratio m/q > 4) from photo-ionization of the tenuous exosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) time-of-flight spectrometer Fast Imaging Plasma Spectrometer (FIPS) has detected many planetary ion species of which He+, the Na+-group (including Na+, Mg+ and Si+) and the O+-group (including O+ and several water group ions) are the most abundant. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) UltraViolet and Visible Spectrometer (UVVS) has also detected Ca+ ions in the nightside plasma sheet. Models of the planetary ion distribution inside Mercury's magnetosphere have mostly concentrated on the abundant Na+ and H+ ion populations. Comparison with FIPS data has been limited to the first two MESSENGER flybys and no comparison has been made with MASCS/UVVS observations.

 

We have developed a Monte Carlo test-particle model which describes the ion density distribution produced from photo-ionization of several neutral species in Mercury's exosphere. The global ion density and energy distribution of Ca+, Mg+, Na+, O+ and He+ will be presented here. We will review the influence of the interplanetary magnetic field (IMF) Bx and By components on the global structure of the ion density distribution, the composition of the nightside plasma sheet and the evolution of the Na+ ion density along the Mercury year.
Using Late Pleistocene SST reconstructions to constrain future greenhouse warming
Authors: Friedrich Tobias , Timmermann Axel
Published: March 2020

Global warming projections for a given anthropogenic greenhouse gas concentration scenario still exhibit a substantial spread.  In order to constrain this spread and to provide robust warming projections, our understanding of Earth's climate sensitivity needs to be further improved. Here, we employ a global network of 64 paleo-proxies of SST to reconstruct global-mean SST variations during the Last Glacial Cycle. This temperature reconstruction is then used as a target function for 25 transient model simulations conducted for the same period with 25 different climate sensitivities. Our combined proxy/model approach allows us to determine an optimal range of model climate sensitivities corresponding to a minimum of the weighted mean squared error calculated for reconstructed and simulated global-mean SSTs. Based on our best estimate, Earth's averaged Late Pleistocene equilibrium climate sensitivity is in the order of ~4.2 K per CO₂ doubling with an associated transient climate response of ~2.4 K/2xCO₂. The latter value translates into a global-mean surface warming of about 5.0 K by the year 2100 (relative to pre-industrial levels) based on the Representative Concentration Pathway 8.5. This warming estimate is in excellent agreement with the ensemble-mean projection of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Error bars resulting from uncertainties in aerosol and ice-sheet forcing as well as in temperature reconstruction clearly document the current limitations for paleo-based constrains of both climate sensitivity and future greenhouse warming and demonstrate the need for more robust forcing and temperature reconstructions that can be utilized to narrow down the spread in global warming projections.

 

 

 

 
Stratospheric sudden warming as a threshold behavior of Rossby waves
Authors: Nakamura Noboru
Published: March 2020

We present evidence that stratospheric sudden warmings (SSWs) are, on average, a threshold behavior of finite-amplitude Rossby waves arising from wave-mean flow interaction. Competition between an increasing wave activity and a decreasing zonal-mean zonal wind sets a limit to the upward wave activity flux of a stationary Rossby wave.  A rapid, spontaneous vortex breakdown occurs once the upwelling wave activity flux reaches the limit, or equivalently, once the zonal-mean zonal wind drops below a certain fraction of the wave-free, reference-state wind obtained from the zonalized quasigeostrophic potential vorticity.  This threshold faction is 0.5 in theory and about 0.3 in reanalyses.  We use the ratio of the zonal-mean zonal wind to the reference-state wind as a local, instantaneous measure of the proximity to vortex breakdown, i.e. preconditioning.  The ratio generally stays above the threshold during strong-vortex winters until a pronounced final warming, whereas during weak-vortex winters it approaches the threshold early in the season, culminating in a precipitous drop in midwinter as SSWs form. The essence of the threshold behavior is captured by a semiempirical 1D model of SSWs, analogous to the “traffic jam” model of Nakamura and Huang for atmospheric blocking. This model predicts salient features of SSWs including rapid vortex breakdown and downward migration of the wave activity/zonal wind anomalies, with analytical expressions for the respective timescales. Model’s response to a variety of transient wave forcing and damping is discussed.

 

 

 

 
Bivergent extension in the overriding plate above a slab tear (Dodecanese, Greece)
Authors: Grasemann Bernhard , Schneider David A. , Soukis Konstantinos , Roche Vincent
Published: March 2020

Tearing in the Hellenic slab below the transition between the Aegean and Anatolian plate is considered to have significantly affected Miocene tectonic and magmatic evolution of the eastern Mediterranean by causing a toroidal flow of asthenosphere and a lateral gradient of extension in the upper plate. Some studies suggest that this lateral gradient is accommodated by a distributed sinistral lithospheric-scale shear zone whereas other studies favor a localized NE-SW striking transfer zone. Recent studies in the northern Dodecanese demonstrate that the transition zone between the Aegean and Anatolian plate is characterized by Miocene extension with a constant NNE-SSW sense of shear accommodating the difference in finite extension rates in the middle-lower crust. Neither localized or distributed strike-slip faults nor rotation of blocks about a vertical axis have been observed.

In this work we focus on the geology Kalymnos located in the central Dodecanese. Based on our new geological map, three major tectonic units can be distinguished: (i) Low-grade, fossil-rich late Paleozoic marbles, which have been deformed into S-vergent folds and out-of-sequence thrusts. This fold-and-thrust belt is sealed by an up to 200 m thick wildflysch-type deposit consisting of low-grade metamorphic radiolarites and conglomerates with tens of meters-scale marbles and ultramafics blocks. (ii) Above this unit, amphibolite facies schists, quartzites and amphibolites are tectonically juxtaposed along a several meter-thick thrust fault with low-grade ultramylonites and cohesive ultracataclasites/pseudotachylites with top-to-N kinematics. (iii) At highest structural levels, a major cataclastic low-angle normal fault zone localized in Verrucano-type violet slates separates Mesozoic unmetamorphosed limestones in the hanging wall. The sense of shear of the normal fault is top-to-SSW. All units are cut by brittle high-angle normal faults shaping the geomorphology of Kalymnos, which is characterized by three major NNW-SSE trending graben systems.

New white mica Ar-Ar ages suggests that the middle units represent relics of a Variscan basement, which was thrusted on top of a fold-and-thrust belt during an Eo-Cimmerian event. Zircon (U-Th)/He ages from the Variscan basement are c. 28 Ma, indicating that the lower units were exhumed below the Mesozoic carbonates during the Oligocene-Miocene. Since Miocene extension in the northern Dodecanese records top-to-NNE kinematics, we suggest that back-arc extension in the whole Aegean realm and transition to the Anatolian plate is bivergent, and tearing in the Hellenic slab did not significantly affected the extension pattern in the upper crust.
Use of carbon-14 and tritium to investigate flow and storage of water in the Christchurch groundwater system
Authors: Stewart Michael , van der Raaij Rob
Published: March 2020

Combined 14C and 3H measurements on groundwater from Christchurch, New Zealand, are proving vitally important for revealing water age distributions, which are key to understanding the diverse flows in the system (including younger potentially polluting water flows from near the surface and much older pristine water flows from depth). The deep gravel aquifers 350-500m thick under Christchurch have been studied since 1970 using 14C along with 3H, 18O and chemical concentrations to characterize the residence times, sources and flowpaths of the water. Of note in this long-term study is the successful use of 14C to determine mean ages of groundwater in the age range from 5 years to 2000 years, which is made possible by the absence of carbonate in the aquifer rocks and the presence of bomb 14C in some samples (Stewart, 2012). The 14C mean ages are showing that the groundwater system has changed markedly over time because of exploitation of the system, from young ages (60-70 years) across the system in 1976 to much older ages (i.e. 400 years on the west and 1600 years on the east) in 2017. Increasing amounts of deep stored water are being tapped by the wells, especially on the east (coastal) side.

Wells on the west side of the system have moderate 14C mean ages (400-600 years) and some of the samples have 3H showing that they also contain fractions of young water. Using binary mixing models allows the proportions and mean ages of the young fractions to be estimated. The mean ages of the young fractions have become younger over time, showing that nitrate contamination is becoming more likely. On the other hand, the fraction of older water is becoming larger and therefore more able to dilute the young fraction. Wells on the east side have much older 14C ages (1600 years) and are 3H-free showing that there are no such younger contributions. The results are providing valuable information for improved understanding and better management of the resource.
Symmetric Instability and Ageostrophic Secondary Circulation in the East Korea Warm Current
Authors: Kim Seongjung , Son Young-Tae , Nam SungHyun
Published: March 2020

Submesoscale dynamics and ocean-atmosphere exchange process in frontal regions play an important role in regulating ocean overturning circulation and cycles of materials (including carbon) and energy, yet our understanding on the dynamics is limited primarily due to lack of relevant observation. To investigate frontal processes such as symmetric instability (SI) and ageostrophic secondary circulation (ASC), multiple comprehensive hydrographic and current observations were made with marine meteorological measurements across a sharp front of the East Korea Warm Current (EKWC) over spring 2017, summer 2017 and fall 2018. Submesoscale features were identified from the observations, estimating diagnostic variables that are the Ertel’s potential vorticity (fq), balanced Richardson number angle ( ), and Ekman buoyancy flux (EBF). The results with fq < 0 along the front,  corresponding to SI regime, and enhanced EBF along the surface of front support that submesoscale overturning circulation induced by down-front wind is due to the SI and ASC. The ASCs with ageostrophic current estimated using the Omega equations further provide vertical motions in the vicinity of the front. Our results suggest that the western boundary currents like EKWC within the North Pacific marginal sea strongly interact with local wind to impact submesoscale overturning circulation and (re-)distribution of materials via SI and ASC.
Quantitative and Comparative Analysis of Slope Instability in Karaj-Chaloos Road (Karaj-Gachsar section) and the Under-Construction Highway of Tehran-North (Tehran-Soleghan section) Using Logistic Regression Method
Authors: Jananeh Keristineh
Published: March 2020

The Karaj-Chaloos road and the Tehran-North highway are two routes that connect the capital Tehran with the southern shores of the Caspian Sea. This contribution aims to study slope instabilities along these roads (Karaj-Gachsar and Tehran-Soleghan sections, respectively) using logistic regression method. In this regard, 14 layers of effective factors were created in the GIS environment and then correlated with the existing instabilities and their density was calculated. Results obtained by applying logistic regression model showed that the most important factors affecting the slope instabilities in the Karaj-Gachsar road area are distance from river, climate and SPI, while those for the Tehran-Soleghan road area are distance from fault and road and climate. According to the prepared maps, the southern and middle parts of the Karaj-Gachsar road, as well as another part in the northwest of the study area have the highest potential for the occurrence of landslides, whereas in the Tehran-Soleghan road area, the middle and southern parts and a small section in the north of the area have the highest potential for landslide occurrence. 34.95% of the Karaj road area has medium to high potential for the occurrence of slope instabilities and 4.97% of this area has very high potential. It is while 27.14% of the Soleghan road area possesses medium to high potential for instabilities and 4.57% of it exhibits very high risk. By comparing these two areas, it is conceivable that areas with medium to high potential of slop instabilities in the Soleghan road area are less than those of the Karaj road area (27.24% and 34.95%, respectively). However, the percentage of instabilities occurred in the Soleghan road area is much higher (86.26%) than the Karaj road area (54.87%). Finally, it can be mentioned that the logistic regression model was effectively applicable for preparing the zonation of the instability occurrence probability along the slopes overlooking the studied roads. It can also be concluded that in addition to natural factors, the human-made factors and particularly unsystematic road construction can play an important role in the landslide occurrences on the slopes overlooking the roads and in order to reduce the relative risks and increase the stability of the slopes, it is necessary to avoid manipulating the ecosystem and changing the current land use as much as possible, along with policy making for constructions in accordance with geomorphological and geological features of the area.
How Earth Scientists Communicate With Maps?
Authors: Pál Márton , Albert Gáspár
Published: March 2020

To communicate the results of a research or scientific facts and theories concerning spatial characteristics, every fields of geoscience use thematic cartography to represent spatial information. Because of this, journals, books and other publications about earth sciences has always needed accurate, reliable and clear methods of map visualization. A map should thematically fit in the body of the publication and should enrich the content. It is an extra task for scientist to take basic cartographic and visual rules into consideration, but with correct methods their publications can earn multiple benefits, such as increased readership and wider dissemination.

When using cartographic methods, we need to find the balance between the triad of i) precision, ii) quality of visual representation and iii) quantity of thematic data. The primary aim is to give an overall ‘image’ of the concerning spatial phenomena that effectively complements the written text of an article. However, these representations sometimes lack some important marks that help the reader to understand the information. Our study focuses on the quality of cartographic visualization in geosciences measuring these marks with the help of an objective system of criteria. These included image quality, cartographic elements that help to locate the studied area (e.g. coordinates), topographic content and copyright rules. By the use of this system we could give grades for each map for each criterion. We have assessed more than 300 maps per field of geoscience (geology, geography, geophysics, meteorology, cartography) in international and Hungarian journals and conference posters.

By summarizing the grades, multiple conclusions can be drawn. We can analyse the map usage habits of each science field: what type of map do they usually use (e.g. thematic or topographic), do they use maps to present results or just give an overview about a studied area and what are the common mistakes that may confuse the reader when interpreting a map. These statistics also hold the opportunity to give advices for each branch to develop their map communication skills. It was also possible to inspect the cartographic practices of each countries. We have found that there is a large spatial variability in the map use habits of different cultures. This can either mean specific but correct ways of visualization or solutions that make the map hard to understand and should not be followed. By examining this spatial factor, proposals concerning objective map element usage can be given to countries or even to whole regions to improve their cartographic communication skills.
Seeing Macro-dispersivity from Hydraulic Conductivity Field with Convolutional Neural Network
Authors: Zhou Zhengkun , Shi Liangsheng , Zha Yuanyuan
Published: March 2020

Building a quantitative relation between the spatial heterogeneity of the hydraulic conductivity fields and the macroscale behavior of solute transport is fundamental for groundwater environment problem. In this work, the deep learning technique is explored to build the functional mapping between the hydraulic conductivity field and the longitudinal macro-dispersivity. We examine the capability of the deep neural network in estimating macro-dispersivities of conductivity fields with different variances. The universality of the trained deep neural network is investigated. Comparisons of the neural network results and the reference values (macro-dispersivities from transport simulation) suggest the promising potential of deep learning technique in porous media with moderate heterogeneity. For a given size of training datasets, the deep neural network produces better macro-dispersivity estimation for the conductivity field with smaller variance. The trained neural network by conductivity fields with larger variance has stronger universality for macro-dispersivity estimation. This study demonstrates that deep neural network can be an effective alternative for predicting macroscale behavior of solute transport by directly interpreting hydraulic conductivity fields.