bluuebunny/crossref_metadata_2025 huggingface dataset:
Lherzolite - carbonatite melt interaction in the presence of additive CO2 and H2O: Experimental data at 5.5 GPa and 1200-1450°C
Authors: Kruk Aleksei , Sokol Alexander
Published: March 2021

We study the reaction of garnet lherzolite with carbonatitic melt rich in molecular CO2 and/or H2O in experiments at 5.5 GPa and 1200-1450°C. The experimental results show that carbonation of olivine with formation of orthopyroxene and magnesite can buffer the CO2 contents in the melt, which impedes immediate separation of CO2 fluid from melt equilibrated with the peridotite source. The solubility of molecular CO2 in melt decreases from 20-25 wt.% at 4.5-6.8 wt.% SiO2 typical of carbonatite to 7-12 wt.% in more silicic kimberlite-like melts with 26-32 wt.% SiO2. Interaction of garnet lherzolite with carbonatitic melt (2:1) in the presence of 2-3 wt.% H2O and 9-13 wt.% molecular CO2 at 1200-1450°С yields low SiO2 (<10 wt.%) alkali‐carbonatite melts, which shows multiphase saturation with magnesite-bearing garnet harzburgite. Thus, carbonatitic melts rich in volatiles can originate in a harzburgite source at moderate temperatures common to continental lithospheric mantle (CLM).

Having separated from the source, carbonatitic magma enriched in molecular CO2 and H2O can rapidly acquire a kimberlitic composition with >25 wt.% SiO2 by dissolution and carbonation of entrapped peridotite. Furthermore, interaction of garnet lherzolite with carbonatitic melt rich in K, CO2, and H2O at 1350°С produces immiscible kimberlite-like carbonate-silicate and K-rich silicate melts. Quenched silicate melt develops lamelli of foam-like vesicular glass. Differentiation of immiscible melts early during ascent may equalize the compositions of kimberlite magmas generated in different CLM sources. The fluid phase can release explosively from ascending magma at lower pressures as a result of SiO2 increase which reduces the solubility of CO2 due to decarbonation reaction of magnesite and orthopyroxene.

The research was performed by a grant of the Russian Science Foundation (19-77-10023).
Shallow crustal structure in the northwestern Iranian Plateau and its tectonic implications
Authors: Wang Xu , Chen Ling , Talebian Morteza , Ai Yinshuang , Jiang Mingming , Yao Huajian , He Yumei , Ghods Abdolreza , Sobouti Farhad , Wan Bo , Chu Yang , Hou Guangbing , Chen Qifu , Xiao Wenjiao , Wu Fuyuan , Zhu Rixiang , Chung Sun-Lin
Published: March 2021

The crustal structure of the Iranian Plateau bears important information about the details of the tectono-magmatic processes associated with the Neo-Tethys subduction and subsequent Arabia-Eurasia collision. Using a newly developed method of joint inversion of multi-frequency waveforms around and horizontal-to-vertical (H/V) ratios of the direct P arrivals in teleseismic P-wave receiver functions, we construct the shear-wave velocity image of the shallow crust (from surface up to 10-km depth below sea level) along a dense seismic array across the Zagros suture in the northwest Iranian Plateau. The most striking structural feature of the study region is the presence of low- and high-velocity anomalies (LVAs and HVAs) beneath the Zagros fold-and-thrust belt and the Iranian continent, respectively, indicating strong structural differences on the two sides of the suture. Systematic analysis on the velocity estimates and comparison with laboratory measurements and regional geology suggest that the LVAs and HVAs are representatives of Zagros sedimentary rocks and arc to intraplate magmatic rocks, respectively. The LVAs (1.3-2.0 km/s) are characterized by a series of faulted anti-form structures at ~1-7 km depths beneath Zagros. They are likely dominantly composed of shales and mudstones, and could have acted as mechanically weaknesses to accommodate different deformations of surroundings and give rise to the present-day depth-dependent seismicity. The HVAs beneath the central domain and Alborz in the Iranian continent present large ranges in both velocity (3.2-3.9 km/s) and depth (0-10 km), probably suggesting strong lithological variations in these areas. Most of the HVAs above 5-km depth have shear-wave velocities of 3.2 to 3.6 km/s, comparable to those of andesites and basalts dominated in the northwestern Iranian plateau. The deeper HVAs (below 5-km depth), which generally have greater velocities ~3.6-3.9 km/s falling into the velocity range of intrusive rocks such as granodiorites, diorites and diabases, appear to have much larger volumes at depth than that exposed on the surface in the study region. Moreover, the surface projections of the HVAs are spatially coincident with the major faults or tectonic boundaries of the region, suggesting a causal link. Our observations provide evidence for not only the lithology-controlled layering in both sedimentary structure and deformation in the Zagros passive margin but also the much more substantial magma generation and emplacement at depth than faulting-facilitated eruption and exposure on the surface in the Iranian active margin during the subduction and collision processes.
Multiple Boris solvers for particle-in-cell (PIC) simulation
Authors: Zenitani Seiji , Kato Tsunehiko
Published: March 2021

 Particle-in-cell (PIC) simulation has long been used in theoretical plasma physics. In PIC simulation, the Boris solver is the de-facto standard for solving particle motion, and it has been used over a half century. Meanwhile, there is a continuous demand for better particle solvers. In this contribution, we introduce a family of Boris-type schemes for integrating the motion of charged particles. We call the new solvers the multiple Boris solvers. The new solvers essentially repeat the standard two-step procedure multiple times in the Lorentz-force part, and we derive a single-step form for arbitrary subcycle number n. The new solvers give n2 times smaller errors, allow larger timesteps, but they are computationally affordable for moderate n. The multiple Boris solvers also reduce a numerical error in long-term plasma motion in a relativistic magnetized flow.

Reference:

S. Zenitani & T. N. Kato, Multiple Boris integrators for particle-in-cell simulation, Comput. Phys. Commun. 247, 106954, doi:10.1016/j.cpc.2019.106954 (2020)
Alpine headwall erosion: Insights from cosmogenic nuclide concentrations in supraglacial debris cover 
Authors: Wetterauer Katharina , Scherler Dirk , Anderson Leif S. , Wittmann Hella
Published: March 2021

Debris-covered glaciers are fed from steep bedrock hillslopes that tower above the ice. These headwalls are eroded by rockfalls and rock avalanches, mobilizing fractured bedrock, which is subsequently deposited on the ice surface along the sides of valley glaciers and transported downglacier on and in the ice. Where glaciers join, marginal debris merges to form medial moraines. Due to the conveyor-belt-nature of glacier ablation zones, debris tends to be older downglacier and, for typical Alpine glaciers, single deposits may persist on the glacier surface for hundreds to a few thousand years.

Recent observations in high-alpine glacial environments suggest that rock walls are increasingly destabilized due to climate warming. An increase in headwall erosion and debris deposition onto glacier surfaces will modify glacial mass balances, as surface debris cover alters the rate at which underlying ice melts. Consequently, we expect that the response of debris-covered glaciers to climate change is likely also related to the response of headwalls to climate change.

In this context, we quantify headwall retreat rates by measuring the concentration of in situ-produced cosmogenic 10Be in debris samples collected from a partly debris-covered Swiss valley glacier. By systematic downglacier-sampling of two parallel medial moraines, we aim to assess changes in headwall erosion through time for small and delineated source areas. Our results indicate that indeed, nuclide concentrations along the medial moraines vary with time: downglacier and further back in time deposits have higher nuclide concentrations, whereas upglacier and more recently deposits have lower concentrations. Currently, we explore possible processes which could account for 10Be concentration changes through time, other than changes in erosion rates. These include the sensitivity of 10Be concentrations to supraglacial transport time and to temporal and spatial changes in nuclide production rates on the deglaciating headwalls. First analyses reveal, however, that neither the additional accumulation of 10Be during transport nor changes in source area production rates associated with the uncovering of formerly ice covered headwall parts alone can account for the observed trend.
Using systematic review to analyse climate change impacts and adaptation associated with mountain permafrost
Authors: Baral Prashant , Allen Simon
Published: March 2021

Mountain permafrost in Asia incorporates permafrost in the mountains of the Hindu Kush Himalayan region, Central Asia, Russia, Mongolia, Qinghai Tibetan plateau and other mountain ranges in China. Changes in climate variables in recent decades have considerably influenced permafrost in these regions and produced vivid impacts. While climate change impacts on mountain permafrost in the alpine regions of Europe, US and Canada are relatively well documented, records about mountain permafrost in Asia are mostly available for the Qinghai Tibetan plateau region and a few other mountain ranges in China. Considerably little information is available for the Hindu Kush Himalayan region and other mountain ranges in Asia. This systematic review analyses climate change related impacts and adaptation in mountain permafrost regions of Asia and attempts to evaluate the status of knowledge based on peer-reviewed journal publications. Impacts on hydrology, geomorphology and ecology were examined and resulting socioeconomic effects were considered. Additionally, ongoing and potential adaptation practices were explored. Warming climate has been found responsible for a gradual shift of the lower limit of mountain permafrost in the region. Increased probabilities of mass wasting events due to reduced slope stability, changes in composition and quality of fresh water resources, irregularities in seasonal flows, changes in permafrost ecosystems and contemporaneous need for the protection of engineered constructions were identified as some of the key impacts. There is a high necessity for increased understanding of mountain permafrost and well-designed response actions to evaluate processes and interactions influencing changes in the natural environment and subsequent effects on sustainable living conditions. Therefore, suitable risk management practices need to be designed with a proper consideration of the anticipated future dynamics of climate, economy and society.
Flow directions of shallow groundwater in a boreal catchment
Authors: Erdbrügger Jana , van Meerveld Ilja , Seibert Jan , Bishop Kevin
Published: March 2021

For most catchments, there is insufficient data to determine the location of the groundwater surface. For humid climates, it is, therefore, often assumed that the groundwater-surface follows the surface topography. This assumption allows using digital elevation models (DEMs) to estimate the flow directions and catchment boundaries. However, high-resolution elevation data also include many small-scale features that are unlikely to affect the direction of groundwater flow, or only affect it during specific conditions. Furthermore, flow directions may change during events or depending on the water level.

The optimal resolution of the DEM for determining groundwater flow directions is not known yet. Therefore, we studied how much DEM derived flow directions and catchment boundaries are affected by the resolution or smoothing of the elevation data for the Krycklan catchment in northern Sweden. We also measured the groundwater levels in two small sub-catchments to determine what DEM resolution best describes the actual groundwater-surface and flow directions.

For the topographic analyses, the LiDAR-based elevation data were first smoothed with various filters (e.g., Gaussian filters) and resampled to obtain lower resolution elevation data. We then determined the flow directions for these different DEMs. The aim was to determine where in the catchment the calculated flow directions are most sensitive to the resolution of the topographic data. The results of the topographic analyses show that for some areas, particularly flat areas, ridges, streambanks and locations where the local slope differs from the general slope, the calculated flow directions depend strongly on the resolution and smoothing of the elevation data.

To test how well the DEM based groundwater flow directions represent actual flow directions, we installed a dense (5-20 m spacing) network of shallow (1 to 6 m deep) groundwater wells (75 wells in total) in a 1 ha and a 2 ha gauged sub-catchment. The triangular nested design of the groundwater well network allowed us to determine the smaller (5 m) and larger scale (20 m) groundwater gradients. The recorded water levels were augmented and validated by manual measurements during the summers of 2018 and 2019. The high spatial and temporal resolution data allowed us to study the response of the groundwater level and the flow directions to different meteorological situations (e.g., large precipitation events after dry and wet conditions and during a very dry period in summer 2018). These observations indicate that the degree to which the groundwater-surface is a subdued copy of the surface topography varies throughout the year, and provides information on which DEM resolution most accurately represents the groundwater-surface and flow directions.
Observed reduction in low-level clouds over the northeastern Pacific attributed to increase in sea surface temperatures
Authors: Andersen Hendrik , Cermak Jan , Zipfel Lukas
Published: March 2021

In this contribution, a significant reduction of low-level marine clouds (LLCs) in the northeastern Pacific is found over a 20-year period in satellite observations and attributed to increasing sea surface temperatures (SSTs).

LLCs play a key role for the Earth’s energy balance, however, their response to climatic changes is not clear, yet. Here, 20 years of Clouds and the Earth’s Radiant Energy System (CERES) cloud observations are analyzed together with reanalysis data sets in multivariate-regression and machine-learning frameworks to link an observed decrease of LLCs in the subtropical northern Pacific to changes in environmental factors. In the analyses, the observed LCC trend is explained almost exclusively by an increase in SSTs, but counteracted to some extent by increased low-level moisture availability. The influence of other factors such as estimated inversion strength, local winds and aerosols is investigated in the statistical frameworks but found to be negligible when compared to the effect of SST changes. The results provide observational evidence for the low-cloud feedback that back model findings of reduced LCC due to increased SSTs in a changing climate.
A modelling framework to predict transpiration reductions during drought based on soil hydraulics 
Authors: Carminati Andrea , Javaux Mathieu
Published: March 2021

There is increasing need for mechanistic and predictive models of transpiration and stomatal response to drought. Global measurements of transpiration showed that the decrease in soil moisture is a primary constrain on transpiration. Additionally, a recent meta-analysis indicated that stomatal closure is explained by the loss in soil hydraulic conductivity, more than that of the xylem. Despite these evidences on the role of soil drying as a key driver of transpiration reduction, the mechanisms by which soil drying impacts transpiration, including the effect of different soil hydraulic properties, are not fully understood.

Here, we propose that stomata regulate transpiration in such a way that the relation between transpiration and the difference in water potential between soil and leaves remains linear during soil drying and increasing vapor pressure deficit (VPD). The onset of hydraulic nonlinearity sets the maximum stomatal conductance at a given soil water potential and VPD. The resulting trajectory of the stomatal conductance for varying soil water potentials and VPD depends on soil and plant hydraulics, with the soil hydraulic conductivity and root length being the most sensitive parameters.

From this hydraulic framework it follows that stomatal closure is not simply a function of soil moisture, soil water potential or leaf water potential. Instead, it depends on transpiration demand and soil-plant hydraulics in a predictable way. The proposed concept allows to predict transpiration reductions during drought with a limited number of parameters: transpiration demand, plant hydraulic conductivity, soil hydraulic conductivity and active root length. In conclusion, this framework highlights the role of the soil hydraulic conductivity as primary constrain on transpiration, and thus on stomatal conductance and photosynthesis.
Impact of Equatorial Atlantic Variability on ENSO Predictive Skill
Authors: Exarchou Eleftheria , Ortega Pablo , Rodrıguez de Fonseca Maria Belén , Losada Doval Teresa , Polo Sanchez Irene , Prodhomme Chloé
Published: March 2021

El Niño–Southern Oscillation (ENSO) is a key mode of climate variability with worldwide climate impacts. Recent studies have highlighted the impact of other tropical oceans on its variability. In particular, observations have demonstrated that summer Atlantic Niños (Niñas) favor the development of Pacific Niñas (Niños) the following winter, but it is unclear how well climate models capture this teleconnection and its role in defining the seasonal predictive skill of ENSO. Here we use an ensemble of seasonal forecast systems to demonstrate that a better representation of equatorial Atlantic variability in summer and its lagged teleconnection mechanism with the Pacific relates to enhanced predictive capacity of autumn/winter ENSO. An additional sensitivity study further shows that correcting SST variability in equatorial Atlantic improves different aspects of forecast skill in the Tropical Pacific, boosting ENSO skill. This study thus emphasizes that new efforts to improve the representation of equatorial Atlantic variability, a region with long standing systematic model biases, can foster predictive skill in the region, the Tropical Pacific and beyond, through the global impacts of ENSO.
Investigating the impact of the Southern Annular Mode on ice-shelf basal melt in Antarctica using a regional ocean model forced by reanalysis data
Authors: Verfaillie Deborah , Pelletier Charles , Goosse Hugues , Jourdain Nicolas , Favier Vincent , Wille Jonathan , Dalaiden Quentin , Fichefet Thierry
Published: March 2021

The climate of polar regions is characterized by large fluctuations and has experienced dramatic changes over the past decades. In the high latitudes of the Southern Hemisphere, the patterns of changes in sea ice and ice sheet mass, in particular, are more complex than for the Northern Hemisphere. Some regions have warmed less than the global average with some sea-ice advance, in particular in the Ross Sea, while other regions such as the Bellingshausen Sea have warmed significantly and displayed sea-ice loss. The Antarctic Ice Sheet has also lost mass in the past decades, with a spectacular thinning and weakening of ice shelves, i.e., the floating extensions of the grounded ice sheet. Despite recent advances in observing and modelling the Antarctic climate, the mechanisms at the origin of those trends are very uncertain because of the limited amount of observations and the large biases of climate models in polar regions, in concert with the large internal variability prevailing in the Antarctic. One of the most important atmospheric modes of climate variability in the Southern Ocean is the Southern Annular Mode (SAM), which represents the position and the strength of the westerly winds. During years with a positive SAM index, lower sea level pressure at high latitudes and higher sea level pressure at low latitudes occur, resulting in a stronger pressure gradient and intensified Westerlies. However, the current knowledge of the impact of these fluctuations of the Westerlies on the Southern Ocean and Antarctic cryosphere is still limited. Some efforts have been devoted over the past few years to the impact of the SAM on the Antarctic sea ice and the surface mass balance of the ice sheet from an atmospheric-specific perspective. Recently, a few studies have focused on the local impact on ice-shelf basal melt in specific regions of Antarctica. However, to our knowledge, there is no such study of the impact of the SAM on ice-shelf basal melt at the pan-Antarctic scale. In this communication, we will address this issue by using simulations performed with the regional ocean and sea-ice model NEMO-LIM3.6 at a spatial resolution of 0.25° forced by the ERA5 reanalysis over the period 1979-2018 CE. The impact of both the annular and the non-annular components of the SAM on ice-shelf basal melt will be assessed through regressions and correlations between the seasonal or annual averages of the SAM index and the ice-shelf basal melt.
Experimental assessment of soil protection by vegetation for current crops and for up-coming EU glyphosate ban
Authors: Stašek Jakub , Krása Josef , Roudnická Adela , Dostál Tomáš , Mistr Martin , Devátý Jan
Published: March 2021

There is still uncertainty in determining vegetation cover and management factor (C factor) for Universal Soil Loss Equation (USLE). Data we use today are often outdated, not specific and not representing local conditions. Current technologies in agriculture and recent crop varieties substantially vary from processes known during USLE (RUSLE) development.

Use of a rainfall simulator on a defined field crop is one way to obtain data for vegetation protection effect. Simulated rainfall is applied on experimental field with crop and bare soil as a reference. Plot size is 8x2 m and runoff and sediment transport is measured. Soil loss ratios are measured for three crop-development stages. Pre-sowing and post-harvest phases are measured as well. All measured data give information about soil protection for the whole season. In the span of 5 years, we have conducted over 340 field experiments on 15 typical, but also newly used crops and various management practices. The results are used in soil erosion and sediment transport analyses or models’ calibration. Metadata of experiments and results are added into a complex and public available database.

The contribution was prepared in the frame of projects No. QK1920224 (Possibilities of anti-erosion protection on farms to avoid the use of glyphosate), and H2020 SHUi (Soil Hydrology research platform underpinning innovation to manage water scarcity in European and Chinese cropping systems).
Comparing impact of ERA5 vs ERAInterim on hydrology using the eWaterCycle Open Hydrological Platform
Authors: Hut Rolf , Drost Niels , Aerts Jerom , Bouaziz Laurene , van Verseveld Willem , Jagers Bert , Baart Fedor , Hoch Jannis , Melsen Lieke , Bennett Andrew , Arnal Lousie , Fenicia Fabrizio , Santos Leonard , Gelati Emiliano , dal Molin Marco , Knoben Wouter , Gharari Shervan , Hall Caitlyn , Hutton Eric ,   the Netherlands eSciencecenter eWaterCycle team
Published: March 2021

Model comparisons are an important exercise to gain new hydrological insight from the diversity in our communities hydrological models. Current practice in model comparison studies is to have each model be run by the creator/representative of that model and combine the results of all these model runs in a single analysis. 

In this work we present the first major model comparison done within the eWaterCycle Open Hydrological Platform. eWaterCycle is a platform for doing hydrological experiments where hydrological models are accessed as objects from an (online) Jupyter notebook experiment environment. Through the use of GRPC4BMI and containers, (pre-existing and newly made) models in any programming language can be used, without diving into the code of those models. This makes eWaterCycle ideally suited to compare (and couple) models with widely different model setups: conceptual versus distributed for example. eWaterCycle is FAIR by design: any eWaterCycle experiment should be reproducible by anyone without the support of the original model developer. This will make it easier for hydrologists to work with each other's models and speed up the cycle of hydrological knowledge generation. 

In this comparison we’re looking at the impact of the new ERA5 dataset over the older ERA-Interim dataset as a forcing for hydrological models. A key component in making hydrological experiments reproducible and transparent in eWaterCycle is the use of EMSValTool as a pre-processor for hydrological experiments. Using EMSValTool’s recipes structure ensures that model specific input files based on ERA5 or ERA-Interim are all handled identically where possible and that model specific operations are clearly and transparently defined. 

We have run 7 models or model-suites (LISFlood, MARRMoT, WFLOW, HYPE, PCRGlobWB 2.0, SUMMA, HBV) for 6 basins forced with both ERA5 and ERA-Interim and compared model outputs against GRDC discharge observations. From this broad comparison we will conclude what the impact of ERA5 over ERA-Interim will be for hydrological modelling in the foreseeable future. 
Spatial Variability of Near-field Ground Motions from Pseudo-Dynamic Rupture Simulations
Authors: Sivasubramonian Jayalakshmi , Mai Paul Martin
Published: March 2021

We analyze the effect of earthquake source parameters on ground-motion variability based on near-field wavefield simulations for large earthquakes. We quantify residuals in simulated ground motion intensities with respect to observed records, the associated variabilities are then quantified with respect to source-to-site distance and azimuth. Additionally, we compute the variabilities due to complexities in rupture models by considering variations in hypocenter location and slip distribution that are implemented a new Pseudo-Dynamic (PD) source parameterization.

In this study, we consider two past events – the Mw 6.9 Iwate Miyagi Earthquake (2008), Japan, and the Mw 6.5 Imperial Valley Earthquake, California (1979). Assuming for each case a 1D velocity structure, we first generate ensembles of rupture models using the pseudo-dynamic approach of Guatteri et.al (2004), by assuming different hypocenter and asperities locations (Mai and Beroza, 2002, Mai et al., 2005; Thingbaijam and Mai, 2016). In order to efficiently include variations in high-frequency radiation, we adopt a PD parameterization for rupture velocity and rise time distribution in our rupture model generator. Overall, we generate a database of rupture models with 50 scenarios for each source parameterization. Synthetic near-field waveforms (0.1-2.5Hz) are computed out to Joyner-Boore distances Rjb ~ 150km using a discrete-wavenumber finite-element method (Olson et al., 1984). Our results show that ground-motion variability is most sensitive to hypocenter locations on the fault plane. We also find that locations of asperities do not alter waveforms significantly for a given hypocenter, rupture velocity and rise time distribution. We compare the scenario-event simulated ground motions with simulations that use the rupture models from the SRCMOD database (Mai and Thingbaijam, 2014), and find that the PD method is capable of reducing the ground motion variability at high frequencies. The PD models are calibrated by comparing the mean residuals with the residuals from SRCMOD models. We present the variability due to each source parameterization as a function of Joyner-Boore distance and azimuth at different natural period.
Linking air stagnation in Europe with the large-scale atmospheric circulation
Authors: Maddison Jacob , Abalos Marta , Barriopedro David , Garcia Herrera Ricardo , Garrido Pérez José  Manuel , Ordóñez Carlos
Published: March 2021

Air stagnation refers to a period when a stable air mass becomes settled over a region and remains quasi-stationary for an extended amount of time. Weak winds in the lower- to mid-troposphere and the absence of precipitation during air stagnation prohibit the ventilation and washout of particles so pollutants can accumulate near the surface. This allows for such pollutants to reach levels harmful to humans, and poses severe health risks. Understanding the development of stagnant conditions is therefore crucial for studying poor air quality and its societal impact. 

Here, the linear relationship between European air stagnation and the large-scale circulation is explored across all seasons and during the 1979--2018 period. Dynamical based indices identifying atmospheric blocking, Rossby wave breaking, subtropical ridges, and the North Atlantic eddy-driven and subtropical jets are used to describe the large-scale circulation as predictors in a statistical model of air stagnation variability. It is found that the large-scale circulation can explain approximately 60% of the variance in monthly air stagnation in five distinct regions within Europe. The variance explained by the model does not vary strongly across regions and seasons. However, the dynamical indices most related to air stagnation do depend on region and season. The blocking and Rossby wave breaking predictors tend to be the most important for describing air stagnation variability in northern regions whereas ridges and the subtropical jet are more important to the south. The demonstrated correspondence between air stagnation and the large-scale circulation can be used to assess the representation of air stagnation in climate models, which is key for understanding how air quality and its associated health risks may change in the future.
Amorphous Si and Ca affect microbial community structure in arctic permafrost soils
Authors: Stimmler Peter , Schaller Jörg
Published: March 2021

Arctic warming affects the permafrost soils in different ways. Increase soil temperature and thawing of deeper horizons modifies the release of greenhouse gases (GHG) by release of nutrients. A lot of research was done about nutrient cycling of C, N and P, but little is known about the influence of Ca and amorphous Si (ASi) on this elements. To show the potential of this two elements in the Arctic systems, we analysed the effect of ASi and Ca on microbial community structure with next generation sequencing and qPCR. We analyzed fungal and bacterial community structure in two different soils from Greenland after incubation with different levels of ASi and Ca. Microbial community reacted differently in the high Arctic (Peary Land) and low Arctic soil (Disko Island) to changing concentrations of ASi and Ca. We found a significant change with linear correlation from gram-negative to gram-positive bacteria classes with increasing Ca and/or ASi levels. Further, abundance of Ascomycota and Basidiomycota changed. We postulate this changes as an important factor for changed GHG production as potential response to modified nutrient availability.
The physical meaning of transport properties evaluated from BTC in karst conduit networks using transfer functions
Authors: Wang Chaoqi , Wang Xiaoguang , Sivelle Vianney , Majdalani Samer , Guinot Vincent , Jourde Hervé
Published: March 2021

The Transfer Function (TF) approach, applying the Laplace transform, is known to be effective in interpreting tracer BreakThrough Curves (BTCs) in karst systems. Although this approach has several advantages over the classical Advection Dispersion Equation (ADE), the parameters of the TF are difficult to interpret directly in terms of transport properties, e.g., flow velocity and dispersion coefficient.

We present two approaches to relate the TF parameters to those of the ADE parameters. The first uses a consistency analysis, the other uses an asymptotic analysis in the Laplace space. The TF parameters can be transformed into equivalent ADE parameter groups that have an apparent physical meaning about the transport process. We further provide guidelines for choosing the suitable fitting models for artificial tracer tests and offer some suggestions for utilizing the TF approach in BTCs interpretation.
Indicators of soil functioning in conventional, conservation and organic agriculture
Authors: Carnol Monique , Chartin Caroline , Krüger Inken , van Wesemael Bas
Published: March 2021

Sustainable management of agricultural systems is a major challenge for ensuring food security of the growing world population. Organic farming and reduced tillage are assumed to be sustainable agricultural practices improving soil quality relative to conventional management strategies. However, assessment of soil quality is often restrained to either physical, chemical or biological parameters. Soil organic carbon (SOC) is the most widely used indicator of soil quality, but it is not necessarily reactive to change, nor representative of the functioning of soil systems, in particular in relation to the realization of soil microbial processes, as it is composed of fractions with different availability for microbial activity and decomposition.

The objective of this study was to assess the influence of three major cropping systems: organic agriculture and conservation agriculture (no/reduced-tillage) vs. conventional agriculture on SOC fractions and microbial processes related to C and N cycling and to establish relationships between carbon fractions and microbial processes in order to identify the most relevant indicator of soil functioning. We hypothesized that 1) organic farming and conservation agriculture would improve soil functioning, 2) labile organic fractions would be better indicators of soil functioning.

We measured C and N in physical and chemical fractions (bulk, <20 µm, 20-2000µm, dissolved organic C, hot water extractable C, water soluble C, K2SO4 extractable C, microbial biomass C) and microbial processes (respiration potential, net N mineralization, metabolic diversity of soil bacteria) in 16 cropland sites in Wallonia, south Belgium (CARBIOSOL project).

Preliminary data analyses indicate improved soil functioning in organic managed sites relative to sites under conventional and conservation management and reveal hot water extractable carbon as a promising proxy for monitoring changes in soil functioning in response to agricultural practices. Final detailed data analyses will be presented.
Sedimentological and environmental approach of the Llumeres offshore sediments (N Asturias-N Spain)
Authors: Flor-Blanco Germán , García-Ordiales Efrén , Ruiz-Quesada Raul , Pando Luis , Flor Germán
Published: March 2021

The sedimentological and geochemical evolution of the internal platform located in front of the Llumeres cove (Asturias, North of Spain) has been studied, based on the analysis of selected sediment samples from 5 long corers, approximately 2 m thick, recovered for an offshore structures installation project. In each sample, a granulometric characterization has been carried out by the calculation of granulometric parameters (centile, mean, shorting, etc.) and the mineralogical composition (silica/biogenic carbonates). Geochemical analysis has also been made in the samples.  The enrichment of selected heavy metals and metalloids (Zn, As, Cu, Pb and Hg) has been studied, applying the Geo-accumulation Index (Igeo) and the Enrichment Factor (EF). The results have also been subjected to multivariate and bivariate statistical analyzes that have allowed establishing the relationships between the elements and determining in a preliminary way their potential origin.

The sedimentological results point to the fact that the sediment was incorporated into the internal platform during the last stages of the sea level rise, which began some 20,000 years ago (Pleisto-Holocene transgression). At present, the zone enjoys stability, since no sedimentation is detected. These sediments are relict, without existing agreement with the siliciclastic sedimentation that is taking place at the moment in the coastal zone (Llumeres beach). Three main sandy lithologies have been analyzed: siliciclastic, mixed and carbonate sands which are distributed irregularly in the vertical. This is indicative of changes in the origin of the sediment (siliciclastic, due to the coastal drift current and bioclastic, typical from the platform), as well as the energy of the depositional agent with a clear decrease in size towards the top, detecting relatively large variations in size and the coarse sediments would correspond to moments of storm.

The geochemical results show that the area does not have a remarkable anthropic condition along the sedimentological profile. However, enrichment of some potential contaminants was detected in the more recent sediments (first centimeters of the boreholes), but the enrichment does not appear to pose an environmental risk and their origin seem to be related to nearby areas such as the Nalón River or the industrial area of Aviles that may export contaminants to the marine environment.
A data-driven approach in the search for Antarctic meteorites
Authors: Tollenaar Veronica , Zekollari Harry , Lhermitte Stef , Tax David , Debaille Vinciane , Goderis Steven , Claeys Philippe , Pattyn Frank
Published: March 2021

Meteorites provide an unparalleled view on the origin and evolution of the solar system. Antarctica is the most productive region for collecting meteorites, as the visually contrasting meteorites are easily detectable and tend to concentrate at specific areas exposing blue ice. Blue ice areas act as meteorite stranding zones if the flow of the ice sheet and specific geographical and climatological settings combine favorably. Previously, possible meteorite stranding zones were identified by chance or through visual examination of remote sensing data, which limits the discovery of new locations for future meteorite searching campaigns.

In this study, various state-of-the-art datasets are combined in a machine learning approach to estimate the likeliness of a blue ice area to be a meteorite stranding zone. Input data for a generative classifier consists of ca. 13,000 reprojected meteorite finding locations (positive observations) and 2,000,000 unlabeled observations, for which the presence of meteorites is unknown. Four features have been selected, representing the typical conditions in which meteorites are found: exposure of blue ice (radar backscatter), cold surface conditions and negative surface mass balance (surface temperature and surface slope), and almost stagnant ice flow (surface velocities). With these features, the probability of the presence of meteorites is computed for each unlabeled observation at blue ice areas. These probabilities are computed by evaluating the multidimensional density distributions of the observations on the unlabeled observations and combining these with the prior probabilities of the two classes (positive and unlabeled). As the set of training data does contain only positive and unlabeled observations, the prior probabilities are scaled. The amount of scaling is decided by maximizing the harmonic mean between precision and sensitivity, which are estimated in a cross-validation using negative observations of sites known to be absent of meteorites. In the post-processing, the pixels that likely contain meteorites are clustered, resulting in several hundreds of meteorite stranding zones.

Results show that the first continent-wide meteorite stranding zone classification is ca. 70-80% accurate (first estimate, based on independent test data). The post-processed results reveal the existence of major unexplored meteorite stranding zones, some of which are in close proximity to existing research stations. The quest to collect the meteorites remaining at the surface of the ice sheet, the number of which is estimated to exceed those already collected to date, will greatly benefit from our newly provided meteorite map.
Seasonal methane and carbon dioxide emissions from the coastal nearshore of the Kolyma river, Siberia.
Authors: Palmtag Juri , Manning Cara , Bedington Michael , Fuchs Matthias , Göckede Mathias , Grosse Guido , Juhls Bennet , Lefebvre Paul , Mollenhauer Gesine , Ogneva Olga , Overduin Paul , Polimene Luca , Strauss Jens , Torres Ricardo , Zimov Nikita , Mann Paul
Published: March 2021

Arctic rivers deliver ≈11% of global river discharge into the Arctic Ocean, while this ocean represents only ≈1% of the global ocean volume. Ongoing climate warming across the Arctic, and specifically Siberia, has led to regional-scale changes in precipitation patterns, greater rates of permafrost thaw and active layer deepening, as well as enhanced riverbank and coastal erosion. Combined, these climatic and cryospheric perturbations have already resulted in increased freshwater discharge and changes to constituent loads (e.g. dissolved organic carbon - OC) supplied from land to the Arctic Ocean.

To date, the majority of studies examining terrestrial organic matter (OM) delivery to the Arctic Ocean have focused almost entirely on freshwater (riverine) or fully-marine environments and been conducted during late summer seasons – often due to logistical constraints. Despite this, an improved understanding of how OC is transformed, mineralised and released during transit through the highly reactive nearshore estuarine environment is critical for examining the fate and influence of terrestrial OM on the Arctic Ocean. Capturing seasonality over the open water period is also necessary to identify current OM fluxes to the ocean vs the atmosphere, and aid in constraining how future changes may modify them.

Here we focus upon carbon dioxide (CO2) and methane (CH4) measurements collected during six repeated transects of the Kolyma River and nearshore zone (covering ~120 km) from 2019. Transects spanned almost the entirety of the riverine open water season (June to September). We use these results, in parallel with gas concentrations derived from prior studies, to develop and validate a simple box-model of gas emissions from the nearshore zone.

Observations and model‐derived output data reveal that more than 50% of the cumulative gross delivery of CH4 and CO2 to the coastal ocean occurred during the freshet period with dissolved CH4 concentrations in surface water reaching 660 Nanomole per liter [nmol/l]. These results demonstrate the relevance of seasonal dynamics and its spatial variability which are needed in order to estimate greenhouse gas fluxes on an annual basis.

More accurate understanding of land-ocean carbon fluxes in the Arctic is therefore crucial to mitigate the effects of climate change and to support the decisions of policy makers.
Exploring winter predictability in Europe using the ECMWF hindcasts
Authors: Mastrangelo Daniele , Giuntoli Ignazio , Malguzzi Piero
Published: March 2021

The accuracy and reliability in predicting winter anomalies, particularly high-impact events, is crucial for economic sectors like energy production and trade. Sub-seasonal predictions can provide a useful tool for early detection of these events. In this context, this study aims to target atmospheric patterns leading to skillful winter predictions at S2S lead times.

With a focus on Europe, we explore extended range predictability (up to 35 days) in the ECMWF hindcast dataset (1999-2018). This dataset provides a sizable sample for assessing the winter months predictive skill of the model and can be considered as a preparatory step to the use of the more comprehensive real-time ensemble forecasts.

The verification is performed on geopotential and temperature fields against the ERA5 reanalysis. We first identify the most skillful predictions both in terms of lead-time and period of initialization. Later we assess whether these skillful predictions correspond to high-impact events, especially cold spells. Finally, in the attempt to identify the potential drivers of improved predictability, we track back to the dominant Euro-Atlantic modes of variability present in the initial atmospheric states of the well predicted events.
3D distinct element back-analysis (static and dynamic) of a reconstructed rock slope
Authors: Mreyen Anne-Sophie , Cauchie Léna , Micu Mihai , Havenith Hans-Balder
Published: March 2021

To better comprehend mechanisms at the origin of natural slope failures, a vast number of potential slope weakening and failure triggering factors ought to be considered. Especially for rather ancient slope failures, such factors can be difficult to identify and strongly depend on the regional to local climatic as well as seismo-tectonic context.

An example of such ancient failure of unknown origin is the Balta rockslide that is located in the seismic region of Vrancea-Buzau, Romanian Carpathians. Even though more superficial landslides are found abundantly in the studied valley, the Balta failure stands out in terms of magnitude and observed geomorphological markers (profound detachment scarp, debris mass accumulation). During the last years, the Balta rockslide has been intensively studied with geophysical measurements (seismic and electrical methods) in order to characterise the landslide and in-situ rock material as well as the extensive dimension of the failure (with an estimated volume of 28.5-33.5 million m³).

In this work, we show the results of a numerical back-analysis of the Balta rockslide based on its reconstructed slope topography, implemented with 3D geomodelling, and on prior established geophysical and geomorphological studies; the reconstruction was furthermore conditioned by the morphology of neighbouring slopes in order to better constrain related uncertainties. The structural aspect of the anti-dip bedding of the sandstone dominated flysch slope was remodelled with 40° dipping discontinuities, while 55° dipping crossing discontinuities represent the main joint family observed in the field. The back-analysis was performed with the 3D distinct element code 3DEC (version 5.2, developed by Itasca) and aims at both, understanding static factors affecting slope stability, as well as the behaviour of the pre-failure slope if subjected to dynamic loading by using a synthetic Ricker multiplier as well as real earthquake acceleration data. The actual slope shape in its post-failure state could be approximated after 120 seconds of ground acceleration and is highlighted by lateral spreading of debris mass as well as towards the valley; the latter supposedly caused a temporary landslide dam formation, and possibly accounts for the river diversion observed in the field. This numerical approach furthermore allows us to outline the main controlling factors during seismic slope excitation that are predominated by topographic and structural site effects.
High-resolution GRACE Monthly Gravity Field Solutions Expressed as Geopotential Coefficients
Authors: Chen Qiujie , Kusche Jürgen , Shen Yunzhong , Zhang Xingfu
Published: March 2021

The commonly used filters (e.g. Gaussian smoothing, decorrelation and DDK filtering) applied to GRACE spherical harmonic gravity field solutions generally lead to reduced resolution, signal damping and leakage. This work is dedicated to improving spatial resolution and reducing signal damping by developing a regularization method with spectral constraints to spherical harmonics. Before constructing the spectral constraints, we create spatial constraints over global grids (covering lands, oceans and the boundaries between lands and oceans) from the a priori information of GRACE spherical harmonic models. Since we are solving geopotential coefficients rather than mascon grids, we further transfer the spatial constraints into the spectral domain according to the law of variance-covariance propagation, leading to spectral constraints regarding geopotential coefficients. In our work, the regularization method with spectral constraints was demonstrated to have comparable ability as mascon modelling method to enhance the spatial resolution and signal power besides reducing signal leakage. Applying the presented method with spatial constraints, we produced the first time series of high-resolution gravity field solutions expressed as geopotential coefficients complete to degree and order 180. Our analyses over the global and regional areas show that our high-resolution solutions are in good agreement with CSR and JPL mascon solutions.