bluuebunny/crossref_metadata_2025 huggingface dataset:
Genesis of felsic and mafic HP granulites from the Moldanubian Zone, Lower Austria
Authors: Hauzenberger Christoph , Schantl Philip , Sizova Elena , Fritz Harald , Finger Fritz , Linner Manfred , Müller Thomas
Published: March 2020

The granulite occurrences from the Moldanubian zone were extensively studied in the last three decades and their metamorphic overprint at high pressures and at UHT conditions are well constrained. However, there are still some discrepancies regarding the prograde PT-path evolution, the genesis of the granulites and the tectonic processes required to produce the proposed PT-paths. Here we present a comprehensive petrological study where we have investigated more than 300 granulite samples from one of the largest occurrences, the Poechlarn-Wieselburg area - Dunkelsteinerwald. Conventional geothermobarometry, garnet zoning pattern, thermodynamic modelling and Zr-in-rutile thermometry on rutile grains enclosed in garnets in felsic and mafic granulites allowed to constrain the prograde as well as the retrograde segments of the PT path. Polycrystalline melt inclusions and high-Ti biotite relics as well as a uniform temperature of approximately 800°C obtained from rutile inclusions (Zr-in-rutile thermometry) in garnet cores disagree with a continuous prograde garnet growth but favour a metastable overstepping of the garnet-in reaction and growth by the peritectic biotite breakdown reaction to garnet and melt within a very narrow PT interval. Subsequent heating to T>1000°C initiated a second stage of garnet growth with a very distinct chemical composition. The preservation of the zoning pattern at these metamorphic conditions clearly document a very short lived process. Diffusion models predict a time span of <5 Ma and cooling rates of 50-60°C/my. Zircon U-Pb ages usually cluster around 340 Ma representing the metamorphic peak. However, in mafic granulites zircon ages from approximately 410 Ma to 340 Ma are obtained indicating either an older formation age for the precursor rock of the mafic granulites or just documenting the occurrence of xenocrysts. We applied a series of coupled petrological–thermomechanical tectono-magmatic numerical model to reproduce our deduced PTt-path that evolved from exhumation of subducted lower crust followed by intense heating at the crust-mantle boundary.
Characterization of heterogeneous landfill: seismic waveform inversion and wavefield retrieval to integrated quantitative inversion of high-resolution seismic-electrical datasets
Authors: Ghose Ranajit
Published: March 2020

A landfill body is typically highly heterogeneous. The scale of these heterogeneities - which are relevant for the purpose of assessment of preferential flow paths, the degradation processes, and the spatio-temporally varying aging and settlements - is quite often small considering the limiting resolution and confidence of the prevalent near-surface geophysical methods. High-density areas act as obstruction to fluid flow and are important for understanding the degradation processes. These areas manifest as scatterers in the recorded seismic wavefield. Strong presence of scattered energy is typical of seismic datasets acquired on landfills. Our research has been concentrated on resolving and monitoring density and porosity variations, as well as distribution of water saturation, phreatic surface, matric suction and stress. Dedicated schemes of early-arrival waveform tomography, full-waveform inversion and interferometric seismic wavefield retrieval complemented by electrical resistivity tomography show promise in high-resolution delineation and monitoring of these properties in a heterogeneous landfill. We will discuss the results of a novel inversion scheme which allows quantitative estimation of spatio-temporally heterogeneous matric suction, stress and porosity.
Vp/Vs ratio and dehydration reactions in subduction zones
Authors: Brantut Nicolas , David Emmanuel
Published: March 2020

High Vp/Vs ratio is a commonly used diagnostic for elevated fluid pressure when interpreting seismological data. The physical basis for this interpretation comes from rock physical data and models of isotropic, cracked rocks. Here, we establish precise conditions under which this interpretation is correct, by using an effective medium approach for fluid-saturated rocks. While the usual result of an increasing Vp/Vs with increasing fluid-saturated porosity holds for crack-like pores, we find that Vp/Vs ratio is not always monotonically increasing with increasing fluid content if the porosity shape deviates from thin cracks, and if the initial Vp/Vs of the rock (without porosity) is already quite high. This is specifically the case of dehydrating rocks, where initial Vp/Vs may already be high (>1.9 for lizardite, for instance), and where the porosity created by the dehydration reaction may be in the form of elongated needles. The model predictions are supported by existing experimental data obtained during dehydration experiments in gypsum and lizardite, which both show a significant decrease in Vp/Vs as dehydration proceeds. Although no experimental data is yet availbale on antigorite, we make a prediction that antigorite dehydration may not lead to any strong increase in Vp/Vs ratio under typical subduction zone conditions. We present our theoretical results in the form of simple closed-form solution (valid asymptotically for a range of limiting cases), which should help guide the interpretation of Vp/Vs ratio from seismological data.
How to reconstruct the geometry of a Middle Triassic feeding system: clues from clinopyroxene textures in lava flows from Cima Pape (Southern Alps, Italy)
Authors: Casetta Federico , Giacomoni Pier Paolo , Nardini Nicolò , Coltorti Massimo
Published: March 2020

Ancient volcano-plutonic complexes can record the evolution of single- or multi-pulse plumbing systems and thus can be used as proxy to investigate the magma dynamics beneath active volcanoes. The exceptional state of conservation of the Middle Triassic Cima Pape complex (Dolomitic Area, Southern Alps) makes it an ideal snapshot of a ~238 Ma old feeding system of a dominantly effusive volcano. It is composed of a 50 to 300 metres thick gabbroic to monzodioritic sill intruded in the sedimentary cover and overlaid by its volcanic counterpart, made up of basaltic to trachyandesitic lavas and pillow breccias. A detailed investigation of the textural and compositional features of clinopyroxene phenocrysts in the volcanites revealed that complex dynamic processes took place in the feeding system beneath the Cima Pape “volcano”. Although some crystals have normal homogeneous or simple-zoned texture, with Mg# [MgO/(MgO+FeOtot) mol%] ranging between 71 and 77 (type 1 clinopyroxene), the great majority of them is typified by a peculiar texture, characterized by the occurrence of intermediate high-Mg# (80-84, up to 90), high-Cr2O3 (up to 1.0 wt%) and low-TiO2 (down to 0.1 wt%) bands (type 2 clinopyroxene). These overgrowths, crystallized between low-Mg# cores and rims, likely indicate that the feeding system was affected by frequent mixing between mafic inputs and differentiated batches. An overview of the main textural/geochemical features of clinopyroxene in effusive and intrusive products was put forward in the present study to reconstruct the main chemico-physical parameters and evolution of the feeding systems beneath the Middle Triassic volcanoes of the Dolomitic Area. Afterwards, these results will be used to advance some speculations about the processes recorded by clinopyroxene crystals in lava flows from active volcanoes, such as Stromboli and/or Mt. Etna.
Electric Field Turbulence in the Solar Wind from MHD down to Electron Scales: Artemis Observations
Authors: Salem Chadi , Bonnell John , Huang Jordan , Hanson Elizabeth , Chaston Christopher , Klein Kristopher , Franci Luca , Verscharen Daniel , Roytershteyn Vadim
Published: March 2020

Recent observational and theoretical work on solar wind turbulence and dissipation suggests that kinetic-scale fluctuations are both heating and isotropizing the solar wind during transit to 1 AU.  The nature of these fluctuations and associated heating processes are poorly understood. Whatever the dissipative process that links the fields and particles - Landau damping, cyclotron damping, stochastic heating, or energization through coherent structures - heating and acceleration of ions and electrons occurs because of electric field fluctuations. The dissipation due to the fluctuations depends intimately upon the temporal and spatial variations of those fluctuations in the plasma frame.  In order to derive that distribution in the plasma frame, one must also use magnetic field and density fluctuations, in addition to electric field fluctuations, as measured in the spacecraft frame (s/c) to help constrain the type of fluctuation and dissipation mechanisms that are at play.

We present here an analysis of electromagnetic fluctuations in the solar wind from MHD scales down to electron scales based on data from the Artemis spacecraft at 1 AU. We focus on a few time intervals of pristine solar wind, covering a reasonable range of solar wind properties (temperature ratios and anisotropies; plasma beta; and solar wind speed). We analyze magnetic, electric field, and density fluctuations from the 0.01 Hz (well in the inertial range) up to 1 kHz. We compute parameters such as the electric to magnetic field ratio, the magnetic compressibility, magnetic helicity, compressibility and other relevant quantities in order to diagnose the nature of the fluctuations at those scales between the ion and electron cyclotron frequencies, extracting information on the dominant modes composing the fluctuations. We also use the linear Vlasov-Maxwell solver, PLUME, to determine the various relevant modes of the plasma with parameters from the observed solar wind intervals. We discuss the results and the relevant modes as well as the major differences between our results in the solar wind and results in the magnetosheath.
Detection of precipitation and snow cover trends in the the European Alps over the last century using model and observational data
Authors: Beaumet Julien , Menegoz Martin , Gallée Hubert , Vionnet Vincent , Fettweis Xavier , Morin Samuel , Blanchet Juliette , Jourdain Nicolas , Wilhelm Bruno , Anquetin Sandrine
Published: March 2020

The European Alps are particularly sensitive to climate change. Compared to temperature, changes in precipitation are more challenging to detect and attribute to ongoing anthropic climate change mainly as a result of large inter-annual variability, lack of reliable measurements at high elevations and opposite signals depending on the season or the elevation considered. However, changes in precipitation and snow cover have significant socio-environmental impact mostly trough water resource availability. These changes are investigated within the framework of the Trajectories initiative (). The variability and changes in precipitation and snow cover in the European Alps has been simulated with the MAR regional climate model at a 7 km horizontal resolution driven by ERA20C (1902-2010) and ERA5 (1979-2018) reanalyses.

For precipitation, MAR outputs were compared with EURO-4M, SAFRAN, SPAZM and E-OBS reanalyses as well as in-situ observations. The model was shown to reproduce correctly seasonal and inter-annual variability. The spatial biases of the model have the same order of magnitude as the differences between the three observational data sets. Model experiment has been used to detect precipitation changes over the last century. An increase in winter precipitation is simulated over the North-western part of the Alps at high altitudes (>1500m). Significant decreases in summer precipitation were found in many low elevation areas, especially the Po Plain while no significant trends where found at high elevations. Because of large internal variability, precipitation changes are significant (pvalue<0.05) only when considering their evolution over long period, typically 60-100 years in both model and observations.

Snow depth and water equivalent (SWE) in the French Alps simulated with MAR have been compared to the SAFRAN-Crocus reanalyses and to in-situ observations. MAR was found to simulate a realistic distribution of SWE as function of the elevation in the French Alpine massifs, although it underestimates SWE at low elevations in the Pre-Alps. Snow cover over the whole European Alps is evaluated using MODIS satellite data. Finally, trends in snow cover and snow depth are highlighted as well as their relationships with the precipitation and temperature changes over the last century.
Sample Position Affect Landslide Susceptibility Models in Hotspot Area of Nam Ma Basin, Lai Chau, Viet Nam
Authors: Chu Van Trung , Chiang Shou-Hao , Lin Tang-Huang
Published: March 2020

The arm of this study to analyze the effect of landslide sample position with point-based approaches for landslide susceptibility modeling which were conducted in the hotspot of the land sliding area located downstream of Nam Ma watershed (Sin Ho, Lai Chau, Viet Nam). Seven hundred fifty-nine landslide polygons that occurred in 2018 were mapped by using google earth integrated with field survey and 84 landslide points extracted from the inventory map conducted in 2013. The state-of-the-art sampling techniques and sample partition approach were applied to produce three subsets of training and testing point-based. Such as the highest position point within landslide polygon (SUB1), the centroid of landslide polygon (SUB2) and the point at the highest position within the seed cell area of the landslide polygon (SUB3). Along with that, the optimal strategy in selecting non-landslide samples was also applied and was first explicitly introduced in this study. Besides, multiple landslide conditioning factors were considered including topographic, geomorphological and hydrological groups. Especially beside of commonly used factors such as slope, elevation, curvature, land use land cover, aspect, etc. the unusual variables also considered such as high above the nearest drainage (HAND - the state-of-the-art terrain) or time series disturbance of land surface index was the first use in this study for landslide analysis and other cutting-edge data processing were proposed in this research arming to optimize the most vital part of whole procedure. The next stage of the analysis is landslide susceptibility modeling. In order to have a more objective judgment about the main issue mentioned above, instead of using only one model, we applied three different models namely Random forest (RF), Logistic regression (LR) and Decision tree (DT) to perform three kinds of scenarios by difference subsets of landslides with five folds of training phase. Subsequently, to compare the abilities of those cases, the model performance was assessed by using the area under the receiver operating characteristic curve both in model success rate (AUCSR) and model predictive rate (AUCPR). Finally, based on the results of this study, all three models performed consistent with three scenarios means the SUB2 and SUB3 are quite similar and much higher than the contribution of SUB1. And the model ability analysis indicated that RF can obtain higher accuracy following by LR and the lowest is DT.

Keywords: Sample position, Landslide Susceptibility, Logistic regression, Random forest, Decision tree, Viet Nam.
Machine Learning-based inference system to detect the phenological stage of a citrus crop for helping deficit irrigation techniques to be automatically applied.
Authors: Forcén Manuel , Pavón Pulido Nieves , Pérez Noguera David , Berríos Reyes Pablo , Pérez Pastor Alejandro , López Riquelme Juan Antonio
Published: March 2020

This paper presents a system that helps farmers to irrigate crops, minimizing water consumption, while productivity is kept, when deficit irrigation techniques are applied, according to the phenological stage of such crop. Such stage is automatically inferred by using a Machine Learning-based technique, which uses single images, which can be acquired by simply using a low cost commercial camera (even the one embedded in a smartphone), as inputs. Specifically, this work compares several Machine Learning approaches, in particular, classical and deep neural networks trained with a dataset obtained from taking multiple real images from a citrus crop. Such images represent different growing stages of the citrus associated to different phenological stages. Since, according to the deficit irrigation approach, the amount of water that can be reduced without affecting the yield depends on the phenological stage of the crop, once such stage is inferred, a Decision Support System uses such information for automatically programming irrigation. The paper also remarks the main advantages of using a single camera as unique sensor in terms of low economic cost as opposed to other systems that uses more expensive and invasive sensors in the crop. In addition, as a smartphone camera could be used as sensor, the smartphone itself could be used as computing device to run the phenological stage detector in real time, and to interact with the Decision Support System by using Cloud and Edge computing technologies. Finally, a set of experiments show the main results obtained after testing different Machine Learning approaches. After comparing such approaches, the best choice is selected to be integrated as a part of the mentioned Decision Support System.
Development of novel ground-based microwave radiometer for earth science -results of the first measurements-
Authors: Ichikawa Ryuichi , Ujihara Hideki , Satoh Shinsuke , Ohta Yusaku , Miyahara Basara , Munekane Hiroshi , Nagasaki Taketo , Tajima Osamu , Araki Kentaro , Tajiri Takuya , Takiguchi Hiroshi , Matsushima Takeshi , Matsushima Nobuo , Momotani Tatsuya , Utsunomiya Kenji
Published: March 2020

We have started to develop a next-generation microwave radiometer to be used in millimeter-wave spectroscopy for the high-resolution and high-precision monitoring of water vapor behavior. The new radiometer will be suitable for not only space geodetic techniques such as VLBI and GNSS, but also field measurements to monitor, for example, volcanic activities and cumulonimbus cloud generation. The planned front-end system for our new microwave radiometer has a wide bandwidth feed of 20–60 GHz. A signal from the feed is separated into two linear orthogonal polarized signals using an orthomode transducer (OMT); one is in the 20–30 GHz feed and the other is in the 50–60 GHz feed. We are now planning to cool the wideband feed, OMT, and LNA for each signal at 77 K using a Stirling cryocooler to improve the signal-to-noise ratio. We assembled a room-temperature 20–30 GHz receiver without the cooling system until the middle of 2019 as a first step of our development. We implemented the new receiver into the 3.7 m dish at Okinawa Electromagnetic Technology Center, National Institute of Information and Communications Technology (NICT), and carried out the first measurements using this receiver for validation tests in October 2019. Quick-look data obtained by the new receiver shows good power signals for the expected receiving band of 18–28 GHz. We are now developing another receiver for a higher band of 50–60 GHz, and we are going to implement the second one into the new prototype radiometer by the end of this fiscal year.
Last Interglacial Sea-Level Indicators in the Western Indian Ocean
Authors: Boyden Patrick , Weil Accardo Jennifer , Deschamps Pierre , Rovere Alessio
Published: March 2020

With global average temperatures 2°C higher than pre-industrial and eustatic sea-level ranging between 5 and 9 m above present, the Last Interglacial is often regarded as a good process-analogue for a future warmer climate.  Large uncertainties are associated with Last Interglacial eustatic sea-level estimations. To quantify these uncertainties through standardization of sea-level metadata, the World Atlas of Last Interglacial Shorelines (WALIS) provides a community-wide standard for documenting the geological context of sea-level indicators and their chronology. By applying this standard, WALIS allows for the quantitative cross-comparison between previous studies, often times separated by decades.

 

We use WALIS to review published sea-level indicators for the Last Interglacial within the Western Indian Ocean basin. Located in the far field with respect to past glaciations, the Western Indian Ocean has the potential to provide precisely measured and dated sea level proxies, enabling a reliable estimation of maximum eustatic sea level for the Last Interglacial. This, in turn, would allow to better constrain upper boundaries of melting within ice-sheet models. Furthermore, this review highlights localities that should be revisited based on the presence of geological facies indicative of former highstands where not enough detail has been reported or where advanced dating and geodetic techniques can increase the accuracy of metadata.
Evolution and Future Architecture for the Earth System Grid Federation
Authors: Kershaw Philip , Abdulla Ghaleb , Ames Sasha , Evans Ben , Landry Tom , Lautenschlager Michael , Balaji Venkatramani , Levavasseur Guillaume
Published: March 2020

The Earth System Grid Federation (ESGF) is a globally distributed e-infrastructure for the hosting and dissemination of climate-related data.  ESGF was originally developed to support the community in the analysis of CMIP5 (5th Coupled Model Intercomparison Project) data in support of the 5th Assessment report made by the IPCC (Intergovernmental Panel on Climate Change).  Recognising the challenge of the large volumes of data concerned and the international nature of the work, a federated system was developed linking together a network of collaborating data providers around the world. This enables users to discover, download and access data through a single unified system such that they can seamlessly pull data from these multiple hosting centres via a common set of APIs.  ESGF has grown to support over 16000 registered users and besides the CMIPs, supports a range of other projects such as the Energy Exascale Earth System Model, Obs4MIPS, CORDEX and the European Space Agency’s Climate Change Initiative Open Data Portal.

Over the course of its evolution, ESGF has pioneered technologies and operational practice for distributed systems including solutions for federated search, metadata modelling and capture, identity management and large scale replication of data.  Now in its tenth year of operation, a major review of the system architecture is underway. For this next generation system, we will be drawing from our experience and lessons learnt running an operational e-infrastructure but also considering other similar systems and initiatives.  These include for example, ESA’s Earth Observation Exploitation Platform Common Architecture, outputs from recent OGC Testbeds and Pangeo (https://pangeo.io/), a community and software stack for the geosciences.   Drawing from our own recent pilot work, we look at the role of cloud computing with its impact on deployment practice and hosting architecture but also new paradigms for massively parallel data storage and access, such as object store. The cloud also offers a potential point of entry for scientists without access to large-scale computing, analysis, and network resources.  As trusted international repositories, the major national computing centres that host and replicate large corpuses of ESGF have increasingly been supporting a broader range of domains and communities in the Earth sciences. We explore the critical role of standards for connecting data and the application of FAIR data principles to ensure free and open access and interoperability with other similar systems in the Earth Sciences.
Characterization and sources of volatile organic compounds (VOCs) during ozone pollution events in Chengdu plain, Southwest China
Authors: Song Mengdi , Li Xin , Yang Suding , Yu Xuena , Chen Shiyi , Dong Huabin , Lou Shengrong , Lu Sihua , Zeng Liming , Lu Keding , Zhang Yuanhang
Published: March 2020

Since 2015, the annual average ozone (O3) concentration in Chengdu has shown significant positive trends and reached a maximum of 55.2 ppb in 2018. By 2019, the annual average O3 value has slightly decreased to 52.9 ppb, but it is still at the highest level in the Sichuan Basin. In order to illuminate VOCs characteristics, identify critical ozone precursors and explore potential sources during ozone pollution events in Chengdu plain, we performed a comprehensive field observation campaign from 9 August to 14 September 2019. During the campaign, the averaged O3 concentration was 29.1 ppb, and mean values of ozone precursors NOx and TVOC were 14.9 ppb and 31.3 ppb, respectively. Two severe ozone pollution events occurred in Chengdu during the observation period. In ozone pollution event 1, the ratios of the average O3, NOx, NMHCs, and OVOCs concentration on the polluted days relative to the clean days were 4.1, 0.3, 0.6, and 1.4, respectively. In ozone pollution event 2, the ratios of the average O3, NOx, NMHCs, and OVOCs concentration on the polluted days relative to the clean days were 3.4, 0.4, 0.6 and 2.1, respectively. The difference of the ratios indicates that there are secondary conversions of NMHCs and NOx and secondary formation of O3 and OVOCs during the pollution period. Isoprene, Acetaldehyde, Methyl Vinyl Ketone, m/p-Xylene and 1-Butene constitute a large fraction of the LOH during polluted days.  In this study, air mass cluster analysis, the potential source contribution function (PSCF), and positive matrix factorization (PMF) receptor models were used in combination to analyze the sources and potential source areas of VOCs during O3 pollution events.
Direct and catalytic contribution of formaldehyde to particulate matter?
Authors: Keutsch Frank , Dovrou Eleni , Bates Kelvin
Published: March 2020

Formaldehyde (HCHO) is produced mainly via photochemical oxidation of volatile organic compounds as well as direct emissions mainly from combustion processes. HCHO has a high vapor pressure but as a result of the hydration of the aldehyde group, it has a Henry’s law constant that allows it to partition into cloud droplets. We present results of two different pathways through which HCHO may contribute to the mass of particulate matter: Formation of hydroxymethanesulfonate (HMS) from reaction of HCHO with dissolved sulfur dioxide (SO2aq) and formation of sulfate by reaction of HCHO with hydrogen peroxide (H2O2) to form hydroxyl methyl hydroperoxide (HMHP), which in turn can oxidize SO2aq to sulfate and reform HCHO. The former pathway contributes to both the carbon and sulfur component of particulate matter whereas the latter contributes to the sulfur particulate budget and suggests a catalytic role of formaldehyde.

We combine laboratory kinetics studies of these reactions with model simulations using GEOS-Chem. The model simulations are analyzed at regional and global scales under present day and simplified preindustrial conditions, in which all anthropogenic emissions are set to zero. The analysis suggests that, depending on conditions, these processes may have significant impact on the sulfur particulate matter budget, specifically the rate of particulate sulfur formation. The results also suggest that under conditions that favor HMS formation, HMS may be the most abundant single organic molecule contributing particulate matter carbon.
Pressure dependence of olivine grain growth at upper mantle conditions
Authors: Ferreira Filippe , Thielmann Marcel , Marquardt Katharina
Published: March 2020

The convective motion of Earth’s upper mantle is controlled by two main deformation mechanisms: grain size-insensitive dislocation creep and grain size sensitive diffusion creep. Grain size thus plays a key role in upper mantle deformation, as it has a significant impact on the viscosity of the upper mantle. Moreover, grain size also affects seismic velocities as well as seismic attenuation.

Despite the importance of grain size and its evolution during deformation, there is still a lack of experimental data on grain growth of olivine at upper mantle pressures. For this reason, we here investigate olivine grain growth at pressures ranging from 1 GPa to 12 GPa and temperatures from 1200 to 1400ºC. The experiments were done using piston cylinder and multi-anvil apparatuses. We used as a starting material olivine aggregates with small amounts of pyroxene (<10%) produced via sol-gel method.

Our results indicate that grain growth is reduced at increasing pressures.  This suggests that the enhanced grain growth due to the temperature increase with depth may be offset, thus facilitating a change from dislocation to diffusion creep in the deep upper mantle. This might have an important impact on the dynamics of the upper mantle.
Paleotemperature and paleosalinity evolution across Eocene-Oligocene Transition in North Atlantic Ocean: Insights from geochemical analysis of bivalve shells.
Authors: Briard Justine , de Rafélis Marc , Vennin Emmanuelle , Daëron Mathieu , Chavagnac Valérie , Emmanuel Laurent , Merle Didier , Pucéat Emmanuelle
Published: March 2020

The Cenozoic period encompasses the last transition from the “greenhouse” climate of the late Early Eocene (~50 Ma) to our modern “icehouse” climate with its much lower CO2 levels, significant polar glaciation and major sea level drop. The Eocene-Oligocene transition (EOT), that marks the first major ice-sheet build-up on Antarctica, has been extensively studied as it represents the entrance into an icehouse mode. Identification of this major step of Antarctic ice-sheet build-up strongly relies on δ18O and Mg/Ca benthic foraminifera records from ODP / DSDP sites. By contrast, few records currently exist from coastal environments despite the presence of abundant fossil archives, like bivalve shells. Yet palaeoenvironmental records from these peculiar coastal sites could bring information on how they react to global climate changes and help to further understand the behavior of our climate system. In this study, we applied a multi-proxy strategy coupling δ18O, δ13C, clumped isotopes (Δ47), strontium isotopes (87Sr/86Sr) analyses on aragonitic and calcitic bivalves and sediments recovered from the Isle of Wight (London-Paris Basin, Northeastern Atlantic Ocean) to provide additional constrain on environmental changes in this region across the Eocene-Oligocene Transition (~37.8–33 Ma).

Our new coupled δ18O and Δ47 dataset highlights a marked decrease in local seawater temperatures (~ 8°C) coupled to a drop in local seawater δ18O, likely linked to the sea level drop associated with ice-cap formation and an evolution toward more proximal, brackish environment in this region (that is apparent from sediment facies evolution). We estimate the salinity decrease recorded at the local scale from the Eocene to the Oligocene as reaching about 6 PSU, from 31 to 25 PSU. Strontium isotope analyses of the bivalves support this interpretation, showing values close to that of seawater up to the EOT but a marked deviation from contemporaneous global seawater 87Sr/86Sr values toward more radiogenic values afterward. This positive deviation is in agreement with an evolution toward more proximal environments, subjected to larger freshwater inputs.
Effect of soil warming and N availability on the fate of recent carbon in subarctic grassland
Authors: Meeran Kathiravan , Verbrigghe Niel , Fuchslueger Lucia , Ingrisch Johannes , Vicca Sara , Soong Jennifer , Müller Lena , Sigurdsson Bjarni D. , Janssens Ivan , Bahn Michael
Published: March 2020

Climate warming has been suggested to impact high latitude grasslands severely, causing considerable carbon (C) losses from soil. Warming can also stimulate nitrogen (N) turnover, but it is largely unclear whether and how altered N availability impacts soil C dynamics. Even less is known about the individual and interactive effects of warming and N availability on the fate of recently photosynthesized C in soil.  We hypothesized that warming would increase belowground C allocation, while enhanced N availability would decrease it, and that their interactive effects would be additive.

We studied a subarctic grassland located at a natural geothermal soil warming gradient close to Hveragerði, Iceland, which was established by an earthquake in 2008. We chose 14 plots along the gradient with soil warming temperatures ranging from 0 to 10°C above ambient, and fertilized a subset of plots with 50kg ha-1 y-1 of NH4NO3 twice a year prior to the study. We performed 13CO2 canopy pulse labeling for an hour and tracked the 13C pulse through the plant-microbe-soil system and into soil respiration for ten days after labeling.

Our preliminary results show that at higher temperatures microbial activity increased, causing higher C turnover and a higher respiration of recently assimilated C from the soil. Warming significantly decreased microbial biomass, however, the recent C allocated from roots to microbes increased. This indicates a higher microbial C-limitation and a tighter root-microbe coupling under warming. Nitrogen addition increased the allocation of recent C to roots, microbial biomass, and soil respiration. The effects of N addition and warming were additive with no interaction. Our results indicate that the microbes in warmed soil may not be N limited, but could be C limited and depend more on the supply of recent C from plants. We conclude that in a future climate with warmer soils, more C may be allocated belowground, however, its residence time may decrease.
FTIR spectral properties affected by OM-cation interactions
Authors: Ellerbrock Ruth , Gerke Horst H.
Published: March 2020

Soil organic matter (OM) interacts with cations like Ca by using C=O and OH functional groups. Such interactions are known to protect soil OM against decomposition. This process affects the bonding strength of functional groups. Changes in bonding strength are assumed to shift the wavenumber region of OH and C=O absorption band maxima in Fourier transform infrared (FTIR) spectra. The aim is to analyze the extent of such shifts to determine presence and strength of OM–cation interaction. Solutions of PGA and Chia seed mucilage were mixed at different ratios with CaCl2 solution. The mixtures were freeze dried. FTIR spectra of PGA–Ca, and mucilage-Ca mixtures indicate that the OH band is affected by the presence of Ca. However, the C=O band maximum and the CH/C=O ratio were not affected. For the PGA–Ca and mucilage-Ca mixtures the shift in OH band maxima relative to PGA and mucilage, respectively, increases with Ca content. Such shifts in OH band maxima are in a similar range as the ones observed for the outer compared to inner regions of an intact chia seed mucilage droplet. The results suggest that it is necessary to know the relation between OM-cation interactions and band shifts for the correct interpretation of the FTIR spectra of soil and rhizosphere samples.
Effect of grain fracture on stick-slip dynamics of granular fault gouge
Authors: Wang Di , Dorostkar Omid , Zhou Wei , Marone Chris , Carmeliet Jan
Published: March 2020

Fault gouge is produced by comminution, wear and other shearing processes that take place during geological tectonic movements. The frictional properties and stick-slip dynamics of granular fault show similar patterns as geophysical phenomena like earthquakes and landslides. In this work, we introduce a particle breakage model in a granular fault system to study the effect of grain fracture on the stick-slip dynamics. Our results show that particle breakage changes the macroscopic friction and the characteristics of slip events. By statistical analyses on a large number of slip events, we find that grain fracture changes the distribution of slip event size. During the evolution of crushable fault gouge, particle breakage does not lead to large slip events but triggers many small slips that partly dissipate the accumulated energy. On the other hand, the grain fracture is also influenced by the slip dynamics: it is shown that larger slip events will lead to a series of particle breakage due to localized high stresses during the rearrangement of granular gouge. Our findings in this study show that in faults with granular gouge particle breakage significantly changes the characteristics of frictional instabilities and affects the dynamics of fault system.
Testing Ambient-Noise Tomography as a Geothermal Exploration Method in Switzerland
Authors: Planès Thomas , Obermann Anne , Antunes Verónica , Lupi Matteo
Published: March 2020

Switzerland is strongly promoting the development of geothermal energy extraction from low- to high-enthalpy resources. However, the broad development of geothermal energy exploitation is hindered by the lack of subsurface knowledge and the high cost of traditional subsurface exploration methods. Affordable passive seismic methods may provide valuable information about the geological structures targeted for geothermal energy extraction. In this context, we are investigating the potential of the Ambient-Noise Tomography (ANT) technique. We present past results obtained from surface-wave ANT in the Geneva basin with a sparse seismic network, and we share preliminary insights from the starting PSIGE project aiming to try refracted P-wave ANT on dense nodal networks (~500 nodes) at several Swiss geothermal exploration sites. From synthetic examples based on prior subsurface models, we discuss the expected depth of investigation and potential resolution of the method with various network configurations. 
Upscaling of geophysical measurements: A methodology for the estimation of the total ground ice content at two study sites in the dry Andes of Chile and Argentina
Authors: Mathys Tamara , Hilbich Christin , Koenig Cassandra E.M. , Arenson Lukas , Hauck Christian
Published: March 2020

With climate change and the associated continuing recession of glaciers, water security, especially in regions depending on the water supply from glaciers, is threatened. In this context, the understanding of permafrost distribution and its degradation is of increasing importance as it is currently debated whether ground ice can be considered as a significant water reservoir and as an alternative resource of fresh water that could potentially moderate water scarcity during dry seasons in the future. Thus, there is a pressing need to better understand how much water is stored as ground ice in areas with extensive permafrost occurrence and how meltwater from permafrost degradation may contribute to the hydrological cycle in the region.

Although permafrost and permafrost landforms in the Central Andes are considered to be abundant and well developed, the data is scarce and understanding of the Andean cryosphere lacking, especially in areas devoid of glaciers and rock glaciers.

In the absence of boreholes and test pits, geophysical investigations are a feasible and cost-effective technique to detect ground ice occurrences within a variety of landforms and substrates. In addition to the geophysical surveys themselves, upscaling techniques are needed to estimate ground ice content, and thereby future water resources, on larger spatial scales. To contribute to reducing the data scarcity regarding ground ice content in the Central Andes, this study focuses on the permafrost distribution and the ground ice content (and its water equivalent) of two catchments in the semi-arid Andes of Chile and Argentina. Geophysical methods (Electrical Resistivity Tomography, ERT and Refraction Seismic Tomography, RST) were used to detect and quantify ground ice in the study regions in the framework of environmental impact assessments in mining areas. Where available, ERT and RST measurements were quantitatively combined to estimate the volumetric ground ice content using the Four Phase Model (Hauck et al., 2011). Furthermore, we developed one of the first methodologies for the upscaling of these geophysical-based ground ice quantifications to an entire catchment in order to estimate the total ground ice volume in the study areas.

In this contribution we will present the geophysical data, the upscaling methodology used to estimate total ground ice content (and water equivalent) of permafrost areas, and some first estimates of total ground ice content in rock glacier and rock glacier free areas and compare them to conventional estimates using remotely sensed data.

 

Hauck, C., Böttcher, M., and Maurer, H. (2011). A new model for estimating subsurface ice content based on combined electrical and seismic datasets, The Cryosphere, 5: 453-468.
Hard thermal turbulence in Antarctic Subglacial Lakes
Authors: Siegert Martin , Couston Louis-Alexandre
Published: March 2020

Over 250 stable and isolated subglacial lakes exist at and close to the ice-sheet center in Antarctica. The physical conditions within subglacial lakes, and the differences between distinct lake settings, are critical to evaluating how and where life may best exist. Here, we demonstrate that upward heating by Earth’s geothermal flux provides efficient stirring of Antarctic subglacial lakes’ water, in a variety of ways related to their water depth, ice overburden and ceiling slope. We show that most lakes are in a regime of hard convective turbulence, enabling efficient mixing of nutrient- and oxygen-enriched top melt-water, which is essential for biome formation. Lakes beneath a thin (about less than 3 km) ice cover and lakes with a thick (more than 3 km) ice cover experience similarly-large velocities, but the latter have significantly larger temperature fluctuations and have a stable layer up to several tens of meters thick adjacent to the ice. We discuss the implications of hydrological conditions on the concentration of particulates in the water column.
Future projections in the climatology of five low-level jets across different CORDEX domains
Authors: Das Sushant , Torres Abraham , Corrales Arturo , Coppola Erika , Giorgi Filippo , Raffaele Francesca , Bukovsky Melissa , Ashfaq Moetasim , Sines Taleena
Published: March 2020

Five of the most prominent low-level jets (LLJs) around the world – the Monsoon Low-Level Jet, Caribbean Low-Level Jet, West African Westerly Jet, Great Plains Low-Level Jet and South American Low-Level Jet – are examined for future climate conditions relative to the present using an ensemble of Regional Climate Model (RCM) simulations under the Coordinated Regional Downscaling Experiment (CORDEX) initiative. The simulations were conducted on a 25 km horizontal grid spacing using lateral and lower boundary forcing from three Coupled Model Inter-comparison Project 5 (CMIP5) global climate models (GCMs) for a near-present historical period (1995–2014) and two future periods (2041–2060 and 2080–2099) under the Representative Concentration Pathway 8.5 (RCP8.5). The RCM is capable of capturing most of the observed climatological features of the LLJs and exhibits a much greater capacity to represent their positioning and core strength compared to the driving GCMs. Analysis of the influence of global warming on the LLJs shows a consistent strengthening of the jets and a shift in their location under both future scenarios. The Monsoon and West African LLJs exhibit a northward shift, while the Caribbean and South American LLJs undergo a westward expansion. The use of an ensemble of high-resolution simulations provides a key element in a robust assessment of changes in LLJs associated with future global-warming scenarios.
Flow regimes, grain mobility and size segregation in stationary bi-disperse granular flows
Authors: Trewhela Tomas , Gray Nico , Ancey Christophe
Published: March 2020

We studied granular flows of glass beads on an inclined conveyor channel. An upward-moving belt conveyed particles that flowed down the channel under the action of gravity, thus creating a stationary flow. To visualize the internal dynamics of the bulk, we relied on the refractive index matching technique. Under fixed slope and belt velocity, we ran mono- and bi-disperse experiments to characterize spatially and temporally the dynamics and concentration fields of these granular flows. Mono-disperse experiments were done using 6 and 8 mm beads on slopes of 10, 12, 15 and 18° and 3 different belt velocities. Beads of 14 mm were added in concentrations of 10, 20, 30 and 40% for the bi-disperse experiments. The rear part of the flow exhibited well-arranged particle layers that moved relatively between them. This particle arrangement ended with a sharp transition to the front of the flow and a dilated convective front. Bi-disperse experiments with low concentrations of large particles conserved the same layered-convective regime with the few added large beads confined to the convective front, a result of size segregation. When the concentration of large beads was increased to 30%, the described regime disappeared. Large grains were frequently dragged back by the belt, thus disrupting the arrangement of particle layers. A quasi-stationary behavior was observed in these experiments, small particles migrated to the front of the flow in pulses that after a while were dragged back, repeating the cycle. We observed that particle concentration fields, on average, were consistent with the structures observed for the  breaking size-segregation wave phenomenon. The effective basal friction, local concentrations and dilation, among other variables, are responsible for these phenomena.
Continuous measurement of open channel discharge using a video data logger and subsequent LSPIV analysis
Authors: Eichendorff Peter , Schlenkhoff Andreas
Published: March 2020

Accurate flow data form the basis for describing hydrological runoff processes and extremes. While the continuous measurement of the water level is a standard task in hydrometry, the continuous measurement of flow velocity is more complex and often involves greater effort. Videometric methods like LSPIV (Large Scale Particle Image Velocimetry) allow a contactless acquisition of surface velocity distribution in open channels. Ready-to-use instrumentation for that purpose is hardly available and requires permanent electricity supply.
Therefore, a simple self-made measuring system, consisting of a data logger with camera and a distance sensor, is introduced. It enables not only the detection of the water level but also the recording and remote transmission of video data. Based on an Arduino microcontroller and a Raspberry Pi Single Board Computer the battery-powered data logger is freely programmable with open source software and supports the operation of various sensors with digital interface at low power consumption. 
The measuring system with its wide angle camera is intended to be mounted on bridges or steep banks with longitudinal or transverse to flow camera alignment. The water level is detected by an ultrasonic range transducer, a raspberry pi camera module with wide angle lens records videos in 1080p resolution.  The water level data and the videos are remotely transmitted via cellular network to a server that provides the data to the subsequent LSPIV analysis. The LSPIV analysis enables a high-resolution measurement of the velocity distribution at the water surface and in combination with the known channel geometry and the height of the water level it offers an accurate discharge determination.
Particularly with regard to extreme events the use of video data brings considerable advantages as it allows a visual on-site inspection of the situation. Information such as the condition of the local vegetation, icing or disturbing influences at the gauge site can be derived and included in the flow rate determination.