bluuebunny/crossref_metadata_2025 huggingface dataset:
Evapotranspiration intensification over unchanged temperate vegetation in the Baltic states is being driven by climate shifts 
Authors: Montibeller Bruno , Jaagus Jaak , Mander Ülo , Uuemaa Evelyn
Published: March 2021

Shifts in climate driven by anthropogenic land use and land cover change are expected to alter various land–atmosphere interactions. Evapotranspiration (ET) is one of these processes and plays a fundamental role in the hydrologic cycle. Using gridded reanalysis and remote sensing data, we investigated the spatiotemporal trends of precipitation, temperature, and ET for croplands and forest areas in the Baltic states where these land cover type had not changed from 2000 to 2018. We focused on ET but investigated the spatiotemporal trends for the three variables at monthly, seasonal, and annual time scales during this period to quantify trade-offs among months and seasons. We used the Mann-Kendall test and Sen’s slope to calculate the trends and rate of change for the three variables. Although precipitation showed fewer statistically significant increasing and decreasing trends due to its high variability, temperature showed only increasing trends in all time scales. The increasing trends were concentrated in late spring (May, +0.14ºC per year), summer (June and August, +0.10ºC), and early autumn (September, +0.13ºC). For unchanged forest and cropland areas, we found no statistically significant ET trends. However, Sen’s slope indicated increasing ET in April, May, June, and September for forest areas and in May and June for cropland. Our results indicate that during the study period, the temperature changes may have lengthened the growing season, which affected the ET patterns of forest and cropland areas. The results also provide important insights into the regional water balance, specially for critical periods where the ET rates increase while precipitation decrease (May, June. and July). Moreover, our study also complements the findings of other studies over the Baltic states.
Circulation patterns in northwest mediterranean harbours based on their geometric characteristics.
Authors: Samper Yaiza , Liste María , Mestres Marc , Espino Manuel , Sanchez Agustín , Sospedra Joaquim , Gonzalez-Marco Daniel , Ruiz Maria Isabel , Álvarez Enrique
Published: March 2021

This paper analyses the summer water circulation in Barcelona, Tarragona and Castellón harbours (east and north-east of Spain), based on field data acquired between April and September 2019. These data include information of wind, waves, 1DV currents, temperature and salinity parameters. The research characterizes the hydrodynamics at the mouth of each harbour and allows to estimate circulation patterns according to its physical characteristics. The availability of simultaneous data on the three harbours allows to analyse and study possible differences. The results show a two-layer circulation in all the harbours. In the cases of Tarragona and Castellón, both with a single mouth, the surface layer flows out of the harbour and the bottom currents circulate inwards. This pattern is reversed in the Barcelona harbour, which has two mouths and is more influenced by the local winds, affecting the distribution of currents in the water column. The bottom water temperature reveals significative differences between the three harbours, especially during the first half of the summer. The results suggest that sea level effects and the water exchange between the harbour and open-sea strongly determine the bottom water temperature. Nevertheless, the sea level series are different in the three harbours. In Barcelona and Tarragona, the meteorological tides are more affected by the atmospheric pressure changes; however, in the case of Castellón, which is smaller, the main influence is associated with the wind, which displaces water and causes a convergence when finding land that results in an increase in sea level. Therefore, the results reveal the importance of knowing the dimensions and morphology of each harbour to describe correctly its hydrodynamics because, despite being under comparable climatic conditions due to their geographical proximity, different hydrodynamic responses are observed to similar atmospheric forcings. The low intensities of the currents and the geometric complexity of the harbour domains, compared to open waters, imply that operational forecasting in these domains can present considerable uncertainties if they are not combined with field data.
Atmospheric Drivers of Melt on Larsen C Ice Shelf: Surface Energy Budget Regimes and the Impact of Foehn
Authors: Elvidge Andy , Kuipers Munneke Peter , King John , Renfrew Ian , Gilbert Ella
Published: March 2021

Recent ice shelf retreat on the east coast of the Antarctic Peninsula has been principally attributed to atmospherically driven melt. However, previous studies on the largest of these ice shelves—Larsen C—have struggled to reconcile atmospheric forcing with observed melt. This study provides the first comprehensive quantification and explanation of the atmospheric drivers of melt across Larsen C, using 31‐months' worth of observations from Cabinet Inlet, a 6‐month, high‐resolution atmospheric model simulation and a novel approach to ascertain the surface energy budget (SEB) regime. The dominant meteorological controls on melt are shown to be the occurrence, strength, and warmth of mountain winds called foehn. At Cabinet Inlet, foehn occurs 15% of the time and causes 45% of melt. The primary effect of foehn on the SEB is elevated turbulent heat fluxes. Under typical, warm foehn conditions, this means elevated surface heating and melting, the intensity of which increases as foehn wind speed increases. Less commonly—due to cooler‐than‐normal foehn winds and/or radiatively warmed ice—the relationship between wind speed and net surface heat flux reverses. This explains the seemingly contradictory results of previous studies. In the model, spatial variability in cumulative melt across Larsen C is largely explained by foehn, with melt maxima in inlets reflecting maxima in foehn wind strength. However, most accumulated melt (58%) occurs due to solar radiation in the absence of foehn. A broad north‐south gradient in melt is explained by the combined influence of foehn and non‐foehn conditions.
Synconvergent and coherent (ultra)high-pressure crustal rock exhumation
Authors: Candioti Lorenzo G. , Vaughan-Hammon Joshua D. , Duretz Thibault , Schmalholz Stefan M.
Published: March 2021

Ultrahigh-pressure (UHP) continental crustal rocks were first discovered in the Western Alps in 1984 and have since then been observed at many convergent plate boundaries worldwide. Unveiling the processes leading to the formation and exhumation of (U)HP metamorphic crustal rocks is key to understand the geodynamic evolution of orogens such as the Alps.

 

Previous numerical studies investigating (U)HP rock exhumation in the Alps predicted deep (>80 km) subduction of crustal rocks and rapid buoyancy-driven exhumation of mainly incoherent (U)HP units, involving significant tectonic mixing forming so-called mélanges. Furthermore, these predictions often rely on excessive erosion or periods of divergent plate motion as important exhumation mechanism. Inconsistent with field observations and natural data, application of these models to the Western Alps was recently criticised.

 

Here, we present models with continuous plate convergence, which exhibit local tectonic-driven upper plate extension enabling compressive- and buoyancy-driven exhumation of coherent (U)HP units along the subduction interface, involving feasible erosion.

 

The two-dimensional petrological-thermo-mechanical numerical models presented here predict both subduction initiation and serpentinite channel formation without any a priori prescription of these two features. The (U)HP units are exhumed coherently, without significant internal deformation. Modelled pressure and temperature trajectories and exhumation velocities of selected crustal units agree with estimates for the Western Alps. The presented models support previous hypotheses of synconvergent exhumation, but do not rely on excessive erosion or divergent plate motion. Thus, our predictions provide new insights into processes leading to the exhumation of coherent (U)HP crustal units consistent with observations and natural data from the Western Alps.
Mercury in permafrost landscapes in the Norwegian Subarctic – current status and potential for increased release and methylation by permafrost thaw
Authors: Nedkvitne Nora , Trier Kjær Sigrid , de Wit Heleen , Westermann Sebastian , Dörsch Peter
Published: March 2021

A vast amount of global mercury is believed to be stored in the Arctic, much of which is frozen in permafrost. Increasing temperatures in the Subarctic, leading to permafrost thaw, alter the global mercury cycle by mobilizing and releasing stored mercury. This is of concern since it allows mercury to spread though air- and waterways. Moreover, mobilized mercury in combination with increased microbial activity can increase the production of methyl mercury (MeHg), a highly potent neurotoxin which readily bioaccumulates throughout food webs. We report current levels of total mercury (HgT) and MeHg for permafrost cores, ambient surface waters, and active layer pore waters across a gradient of sporadic permafrost (peat plateaus) ranging from coastal-mild to inland-cold climate in the northernmost part of continental Europe (Finnmark, Norway). To investigate the effect of microbial activity on mercury methylation, permafrost samples were thawed and subjected to long-term incubation under oxic, and oxic/anoxic conditions, with and without additional native DOC and extraneous C, N, P, S, and Hg additions. Microbial activity was monitored by CO2 and CH4 production. Our field samples indicate that the %MeHg of HgT are higher in the outlet of the peat plateau than in the inlet and that streams have a significantly higher %MeHg of HgT than ponds. In contrast, thermokarst ponds (collapsed peat plateaus) have a significantly higher concentration of HgT than streams. In the incubation experiments, presence or absence of oxygen had the largest impact on DOC and dissolved HgT accumulation; soil slurries incubated under anoxic conditions yielded higher concentrations of both DOC and dissolved HgT compared to oxic conditions. Selected results from ongoing experiments will be presented.
Sequential Aggregation of Probabilistic Forecasts - Applicaton to Wind Speed Ensemble Forecasts
Authors: Zamo Michael , Bel Liliane , Mestre Olivier
Published: March 2021

Sequential aggregation is a theoretically-grounded means to combine several forecasts of a quantity to achieve better forecast performance as evaluated by a loss function. This theory has been mainly applied to point forecasts with a scalar forecast quantity, but rarely to forecasts expressed in a probabilistic form. In this work, we show how this theory can be readily adapted to forecasts expressed as step-wise cumulative distribution function (CDF), with the continuous ranked probabilistic score (CRPS) as performance measure.

Ensemble weather forecasts estimate the outcome of future observed quantities in a way that can be interpreted as step-wise CDF. Since those forecast CDFs are biased, statistical postprocessing methods are used to improve their statistical coherency with the observed quantity. Since many ensembles and many postprocessing methods exist, one can combine raw and post-processed ensembles in order to get even better forecast performance. To illustrate this point and the advantages of blending CDFs, sequential aggregation is applied to wind-speed ensemble weather forecasts with the CRPS as a performance measure alongside the Jolliffe-Primo test to assess the reliability of the various (raw, post-processed or aggregated) forecasts.
Using new observations and Machine Learning to improve organic sinking processes in the PlankTOM global ocean biogeochemical model 
Authors: Denvil-Sommer Anna , Le Quéré Corinne , Buitenhuis Erik , Guidi Lionel , Irisson Jean-Olivier
Published: March 2021

A lot of effort has been put in the representation of surface ecosystem processes in global carbon cycle models, in particular through the grouping of organisms into Plankton Functional Types (PFTs) which have specific influences on the carbon cycle. In contrast, the transfer of ecosystem dynamics into carbon export to the deep ocean has received much less attention, so that changes in the representation of the PFTs do not necessarily translate into changes in sinking of particulate matter. Models constrain the air-sea CO2 flux by drawing down carbon into the ocean interior. This export flux is five times as large as the CO2 emitted to the atmosphere by human activities. When carbon is transported from the surface to intermediate and deep ocean, more CO2 can be absorbed at the surface. Therefore, even small variability in sinking organic carbon fluxes can have a large impact on air-sea CO2 fluxes, and on the amount of CO2 emissions that remain in the atmosphere.

In this work we focus on the representation of organic matter sinking in global biogeochemical models, using the PlankTOM model in its latest version representing 12 PFTs. We develop and test a methodology that will enable the systematic use of new observations to constrain sinking processes in the model. The approach is based on a Neural Network (NN) and is applied to the PlankTOM model output to test its ability to reconstruction small and large particulate organic carbon with a limited number of observations. We test the information content of geographical variables (location, depth, time of year), physical conditions (temperature, mixing depth, nutrients), and ecosystem information (CHL a, PFTs). These predictors are used in the NN to test their influence on the model-generation of organic particles and the robustness of the results. We show preliminary results using the NN approach with real plankton and particle size distribution observations from the Underwater Vision Profiler (UVP) and plankton diversity data from Tara Oceans expeditions and discuss limitations.
Depth-dependent decomposition of root litter in drained and rewetted fen ecosystems
Authors: Blume-Werry Gesche , Kreyling Juergen , Schwieger Sarah , Eckhardt Kai-Uwe , Henningsen Levke , Hogrefe Hans , Wrage-Mönnig Nicole , Mueller Juergen , Leinweber Peter
Published: March 2021

Peatlands cover only 3% of the lands surface, but store roughly a third of the global soil carbon due to inhibited decomposition rates. Over a third of the peatland area in Europe are fens, in which the peat is primarily formed by roots and rhizomes of vascular plants. These fens have been subjected to widespread drainage and conversion into agricultural areas. As a result, they continuously emit large amount of greenhouse gases. One strategy of mitigating the emissions, and ideally restoring the original sink function, is to rewet fen peatlands. However, it remains uncertain how rewetting changes decomposition rates compared to the drained state, and what the underlying biogeochemical processes and organic matter transformations during litter decomposition and peat formation are. We here present decomposition rates of root material in different depth, over 6 months, a year, and two years in different drained and rewetted fen ecosystems (percolation fen, coastal fen, alder forest). In addition to mass loss, we also assessed the composition of carbon compounds over time.
Micro-mechanical modeling using DEM to study the effect of mechanical properties on crack propagation for snow slab avalanches
Authors: Gregoire Bobillier , Bastian Bergfled , Johan Gaume , Alec van Herwijnen , Jürg Schweizer
Published: March 2021

Dry-snow slab avalanche release is a multi-scale process starting with the formation of localized failure in a highly porous weak snow layer below a cohesive snow slab, which can be followed by rapid crack propagation within the weak layer. Finally, a tensile fracture through the slab leads to its detachment. About 15 years ago, the propagation saw test (PST) was developed. The PST is a fracture mechanical field test that provides information on crack propagation propensity in weak snowpack layers. It has become a valuable research tool to investigate the processes involved in crack propagation. While this has led to a better understanding of the onset of crack propagation, much less is known about the ensuing propagation dynamics. Here, we use the discrete element method to numerically simulate PSTs in 3D and analyze the fracture dynamics using a micro-mechanical approach. Our DEM model reproduced the observed PST behavior extracted from experimental analysis. We developed different indicators to define the crack tip that allowed deriving crack speed. Our results show that crack propagation in level terrain reaches a stationary speed if the snow column is long enough. Moreover, we define stress concentration sections. Their length evolution during crack propagation suggests the development of a steady-state stress regime. Slab and weak layer elastic modulus, as well as weak layer shear strength, are the key input parameters for modeling crack propagation; they affect stress concentrations, crack speed, and the critical length for the onset of crack propagation. The results of our sensitivity study highlight the effect of these mechanical parameters on the emergence of a steady-state propagation regime and consequences for dry-snow slab avalanche release. Our DEM approach opens the possibility for a comprehensive study on the influence of the snowpack mechanical properties on the fundamental processes for avalanche release.
Past trends in precipitation and in the ratio of snow to rain in East Greenland
Authors: van der Schot Jorrit
Published: March 2021

Climate models project a strong increase in Arctic precipitation as well as an increase in the ratio of liquid to solid precipitation for the 21st century. While previous studies have explored past trends in precipitation, relatively little is known about the trends in the ratio of liquid to solid precipitation. A regression analysis of the ratio of liquid to solid precipitation in East Greenland will be conducted to better understand if and how precipitation as well as the relative fractions of snow and rain in precipitation have changed in the time period 1958-2019. This will be done in the context of the interdisciplinary project Snow2Rain which focusses on understanding how the transition from snow to rain is influencing quality of life in and around Tasiilaq (Southeast Greenland). Here, in a broader geographical context, a combination of results from the Regional Atmospheric Climate Model (RACMO2.3p2) and meteorological observations from weather stations along the coast of East Greenland between 65° N and 70° N will be used to assess changes in the ratio of liquid to solid precipitation. The station data will serve to cross-check the output from the regional climate model. A simple partitioning scheme based on near-surface temperature will be used. The combination of model data and weather observations can increase our understanding of trends in the relative fraction of precipitation that falls as snow or rain along the data sparse Greenlandic East coast.
Interactive visualization and topology-based analysis of large-scale time-varying remote-sensing data: challenges and opportunities
Authors: Fellegara Riccardo , Flatken Markus , De Zan Francesco , Gerndt Andreas
Published: March 2021

Over the last few years, the amount of large and complex data in the public domain has increased enormously and new challenges arose in the representation, analysis and visualization of such data. Considering the number of space missions that provided and will provide remote sensing data, there is still the need of a system that can be dispatched in several remote repositories and being accessible from a single client of commodity hardware.

To tackle this challenge, at the DLR Institute for Software Technology we have defined a dual backend frontend system, enabling the interactive analysis and visualization of large-scale remote sensing data. The basis for all visualization and interaction approaches is CosmoScout VR, a visualization tool developed internally at DLR, and publicly available on Github, that allows the visualization of complex planetary data and large simulation data in real-time. The dual component of this system is based on an MPI framework, called Viracocha, that enables the analysis of large data remotely, and allows the efficient network usage about sending compact and partial results for interactive visualization in CosmoScout as soon as they are computed.

A node-based interface is defined within the visualization tool, and this lets a domain expert to easily define customized pipelines for processing and visualizing the remote data. Each “node” of this interface is either linked with a feature extraction module, defined in Viracocha, or to a rendering module defined directly in CosmoScout. Being this interface completely customizable by a user, multiple pipelines can be defined over the same dataset to enhance even more the visualization feedback for analysis purposes.

Being an ongoing project, on top of these tools, as a novel strategy in EO data processing and visualization, we plan to define and implement strategies based on Topological Data Analysis (TDA). TDA is an emerging set of technique for processing the data considering its topological features. These include both the geometric information associated to a point, as well all the non-geometric scalar values, like temperature and pressure, to name a few, that can be captured during a monitoring mission. One of the major theories behind TDA is Discrete Morse Theory, that, given a scalar value, is used to define a gradient on such function, extract the critical points, identify the region-of-influence of each critical point, and so on. This strategy is parameter free and enables a domain scientist to process large datasets without a prior knowledge of it.

An interesting research question, that it will be investigated during this project is the correlation of changes of critical points at different time steps, and the identification of deformation (or changes) across time in the original dataset.
Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern Germany
Authors: Polom Ulrich , Mecking Rebekka , Leineweber Phillip , Omlin Andreas
Published: March 2021

In the North German Basin salt tectonics generated a wide range of evaporite structures since the Upper Triassic, resulting in e.g. extended salt walls, salt diapirs, and salt pillows in the depth range up to 8 km. Due to their trap and seal properties these structures were in the focus of hydrocarbon exploration over many decades, leading to an excellent mapping of their geometries below 300 m in depth. During salt rise Rotliegend formations were partly involved as a constituent. Some structures penetrated the salt table, some also the former surface. Dissolution (subrosion) and erosion of the salt cap rock by meteoric water took place, combined with several glacial and intraglacial overprints. Finally the salt structures were covered by pleistocene and holocene sediments. This situation partly resulted in proneness for ongoing karstification of the salt cap rock, leading to e.g. local subsidence and sinkhole occurrence at the surface. The geometry, structure and internal lithology of these shallow salt cap rocks are widely unknown. Expanding urban and industrial development, water resources management and increasing climate change effects enhance the demands for shallow mapping and characterization of these structures regarding save building grounds and sustainable water resources.

Results of shallow drilling investigations of the salt cap rock and the overburden show unexpectedly heterogenous subsurface conditions, yielding to limited success towards mapping and characterization. Thus, shallow high-resolution geophysical methods are in demand to close the gaps with preferred focus of applicability in urban and industrial environments. Method evaluations starting in 2010 geared towards shallow high-resolution reflection seismic to meet the requirements of both depth penetration and structure resolution. Since 2017 a combination of S-wave and P-wave seismic methods including depth calibrations by Vertical Seismic Profiling (VSP) enabled 2.5D subsurface imaging starting few meters below the surface up to several hundred meters depth in 0.5-5 m resolution range, respectively. The resulting profiles image strong variations along the boundaries and on top of the salt cap rock. Beside improved mapping capabilities, aim of research is the development of characteristic data features to differentiate save and non-save areas.
On the Seasonal variability eastern boundary of the North Atlantic Subtropical Gyre
Authors: Pérez-Hernández Maria Dolores , Vélez-Belchí Pedro , Caínzos Verónica , Santana-Toscano Daniel , Arumí-Planas Cristina , Cubas Armas Melania , Presas Navarro Carmen , Hernández-Guerra Alonso
Published: March 2021

On the eastern region of the North Atlantic Subtropical Gyre, the Canary Current connects the Azores Current with the North Equatorial Current. Several studies link the seasonality of the AMOC (as measured by the RAPID program) to the seasonality of the main flows existing on the Canary basin. Since 2003, the RaProCan project which is the Canary Islands component of the Spanish Institute of Oceanography ocean observing system, monitors the Canary basin. In 2015, the RaProCan project joined efforts with the Seasonal Variability of the AMOC: Canary Current (SeVaCan) project of the Instituto de Oceanografía y Cambio Global (IOCAG) to increase the temporal resolution of the observations. Hence, during 2015 a hydrographic cruise took place in each season (February, April, July, and November) to complete the seasonal cycle of the basin. Here we present results from these cruises to describe the seasonal cycle of the area. A sensitive analysis is carried out to understand the representativeness of the cycle to be able to compare it with the AMOC seasonal cycle.
Laplacian structure mirroring surface topography in determining the gravity potential by successive approximations
Authors: Holota Petr , Nesvadba Otakar
Published: March 2021

Similarly as in other branches of engineering and mathematical physics, a transformation of coordinates is applied in treating the geodetic boundary value problem. It offers a possibility to use an alternative between the boundary complexity and the complexity of the coefficients of the partial differential equation governing the solution. In our case the Laplace operator has a relatively simple structure in terms of spherical or ellipsoidal coordinates which are frequently used in geodesy. However, the physical surface of the Earth and thus also the solution domain substantially differ from a sphere or an oblate ellipsoid of revolution, even if optimally fitted. The situation becomes more convenient in a system of general curvilinear coordinates such that the physical surface of the Earth is imbedded in the family of coordinate surfaces. Applying tensor calculus the Laplace operator is expressed in the new coordinates. However, its structure is more complicated in this case and in a sense it represents the topography of the physical surface of the Earth. The Green’s function method together with the method of successive approximations is used for the solution of the geodetic boundary value problem expressed in terms of the new coordinates. The structure of iteration steps is analyzed and if useful and possible, it is modified by means of integration by parts. Subsequently, the iteration steps and their convergence are discussed and interpreted, numerically as well as in terms of functional analysis.
Spatially resolved evaluation of Earth system models with satellite column-averaged CO2
Authors: Gier Bettina K. , Buchwitz Michael , Reuter Maximilian , Cox Peter M. , Friedlingstein Pierre , Eyring Veronika
Published: March 2021

Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) showed large uncertainties in simulating atmospheric CO2 concentrations. We utilize the Earth System Model Evaluation Tool (ESMValTool) to evaluate emission-driven CMIP5 and CMIP6 simulations with satellite data of column-average CO2 mole fractions (XCO2). XCO2 time series show a large spread among the model ensembles both in CMIP5 and CMIP6. Using the satellite observations as reference, the CMIP6 models have a lower bias in the the multi-model mean than CMIP5, but the spread remains large. The satellite data are a combined data product covering the period 2003–2014 based on the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)/Envisat (2003–2012) and Thermal And Near infrared Sensor for carbon Observation Fourier transform spectrometer/Greenhouse Gases Observing Satellite (TANSO-FTS/GOSAT) (2009–2014) instruments. While the combined satellite product shows a strong negative trend of decreasing seasonal cycle amplitude (SCA) with increasing XCO2 in the northern midlatitudes, both CMIP ensembles instead show a non-significant positive trend in the multi-model mean. The negative trend is reproduced by the models when sampling them as the observations, attributing it to sampling characteristics. Applying a mask of the mean data coverage of each satellite to the models, the SCA is higher for the SCIAMACHY/Envisat mask than when using the TANSO-FTS/GOSAT mask. This induces an artificial negative trend when using observational sampling over the full period, as SCIAMACHY/Envisat covers the early period until 2012, with TANSO-FTS/GOSAT measurements starting in 2009. Overall, the CMIP6 ensemble shows better agreement with the satellite data than the CMIP5 ensemble in all considered quantities (mean XCO2, growth rate, SCA and trend in SCA). This study shows that the availability of column-integral CO2 from satellite provides a promising new way to evaluate the performance of Earth system models on a global scale, complementing existing studies that are based on in situ measurements from single ground-based stations.
Towards a description of stick-slip motion using a viscoelastic Full Stokes model 
Authors: Gerli Cristina , Rosier Sebastian , Gudmundsson Hilmar
Published: March 2021

The lightly grounded portion of the Whillans Ice Stream (WIS, Siple Coast, Antarctica), has a unique stick-slip motion behaviour, where prolonged stagnant phases (6-25 hrs) are interrupted by rapid active slip events (up to 0.5 m in < 1 hr).  WIS is also interesting because it is currently stagnating, presenting an important opportunity to understand this behaviour and its effect on future sea level rise. Detailed observations and a variety of modelling approaches have revealed the complexity of stick-slip behaviour and the importance of correctly representing ice rheology, ice stream geometry, spatial variability of friction strength, and boundary conditions. Currently, no single model exists that can fully replicate all the observed features of stick-slip motion as observed on the Whillans Ice Plain. Here we describe a full-Stokes viscoelastic finite element model that has been previously used to explore tidal modulation of ice stream flow, and which can overcome some of the assumptions adopted in previous work. The model is  set up for an idealised configuration of the Whillans Ice Plain, with the aim of exploring how the inclusion of relevant additional physics affects stick-slip motion for a rate and state friction law, and whether other sliding laws could also explain the observed motion. Ultimately, this modelling work aims to put tighter constraints on the conditions required to initiate stick-slip behaviour, improving our understanding of basal sliding and future sea level rise.
Mineralogical composition of terrestrial feldspathic rocks using reflectance spectroscopy data from HySpex hyperspectral cameras
Authors: Barthez Marie , Flahaut Jessica , Ito Gen , Hernandez-Palacios Julio , Liu Na , Pik Raphaël
Published: March 2021

New feldspar detections made by visible-near infrared (VNIR) spectroscopy last year on Mars [1], raise questions on the nature of the rocks involved and the magmatic processes responsible for their formation.

Following these new findings, a range of terrestrial feldspathic rocks, which are possible analogs to the feldspar-bearing Martian rocks, were analyzed using a VNIR point-spectrometer (ASD Fieldspec 4) in a laboratory [2]. A spectral library referencing the average reflectance spectrum of uncrushed terrestrial feldspathic rocks, including granites, granodiorites, phenocryst basalts, dacites, anorthosites, was assembled. One of the conclusions from this work was that a more detailed, grain-by-grain spectral analysis is needed.

In this study we used a new instrument that made it possible to determine the grain-by-grain mineralogical composition of these same terrestrial analog rocks. VNIR spectra were acquired with the HySpex hyperspectral cameras VNIR-1800 and SWIR-384 that acquire high-resolution data in the visible near-infrared and short-wave infrared wavelength ranges. The cameras image the scene line by line using the pushbroom scanning technique. Using interchangeable lenses, cameras were used to acquire spectroscopy data at a distance of 30cm and at 8cm from the sample. In the VNIR, this results in a pixel size of about 53 µm and 24µm at sample-sensor distance of 30cm and 8cm, respectively, while in the SWIR, the pixel size is 250 µm and 55µm at a distance of at 30cm and 8cm, respectively. The hyperspectral cubes are analyzed with the ENVI software to classify the image pixels according to their spectral signature. Thus, the different minerals present in the rock, which are often on a millimeter scale, are grouped into different classes. The statistics give the average spectrum of each class, and therefore each mineral group.

This study, complementary to that of Barthez et al. (2020), makes it possible to associate, for each studied rock sample, an average reflectance spectrum of the bulk rock to a precise mapping of the different minerals present in the rock. This study allows us to determine if the feldspar minerals are contributing to the observed rock spectrum, and to assess each mineral group’s contribution to the spectral signature of the whole rock. Detailed petrographic characterization of rocks are also being conducted to evaluate characterizations done with spectral data.

 

References

[1] J.Flahaut et al. (2020). EGU Abstracts, EGU2020-13377

[2] M.Barthez et al. (2020). EPSC Abstracts, EPSC2020-606
Exploring the causes of glacier velocity anomalies in High Mountain Asia: Analysis from the Karakoram, Spiti Lahaul and Eastern Himalaya
Authors: Curry Charlotte S. , Rowan Ann V. , Ng Felix S. L.
Published: March 2021

Glaciers in High Mountain Asia (HMA) have been experiencing enhanced mass loss and velocity slowdown since the late 1990s, coincident with rising global and regional temperatures. In each HMA region with distinct climatic characteristics, the dynamical responses of glaciers vary substantially; yet these intra-regional variations are overlooked in regional assessments due to large-scale oversampling. In particular, the role of glacier morphological factors (e.g. size, elevation, hypsometry) in causing the different responses is poorly understood.

We investigated the velocity changes of the glaciers in three regions — the Eastern Himalaya, Spiti Lahaul, and Karakoram — between 2000 and 2016 in order to understand the key components of glacier sensitivity and their relationship with glacier morphology. Using the NASA Inter-Mission Time Series of Land Ice Velocity and Elevation dataset as input, we extracted glacier-specific velocities (and associated errors) using a bespoke MATLAB script, and compiled these into “mean annual velocity anomaly” series following established methods. Anomalies were analysed with glacier morphometric parameters using a linear regression approach, with statistically significant relationships identified.

Our results show that mean velocity anomaly within the Eastern Himalaya varies with glacier aspect, with mean annual anomalies of 0.09 ± 2.32 m yr-1 per year for north-flowing glaciers and –0.1 ± 1.59 m yr-1 per year for south-flowing glaciers. Glaciers in the Karakoram also show opposing trends, with anomalies of –0.86 ± 5.69 m yr-1 per year and –3.23 ± 2.53 m yr-1 per year in the north west, and 1.00 ± 3.80 m yr-1 per year in the south east. Glacier slowdown in Spiti Lahaul is –0.37 ± 4.50 m yr-1 per year, and we do not document contrasts in intra-regional glacier response. Overall, glacier size, minimum elevation and hypsometric integral are the most significantly correlated parameters to mean velocity anomaly. Percentage and area of debris, flow line length, slope and termination environment were also found to be important autocorrelations. Importantly, we find no consistent morphometric interactions contributing to glacier anomaly between all three regions, implying that glacier responses are unique and a cumulative product of their morphometric variability.
Modelling Nature-based Solutions: an application to mitigate coastal erosion
Authors: Unguendoli Silvia , Valentini Andrea , Germano Biolchi Luis , Pranavam Ayyappan Pillai Umesh , Jacopo Alessandri , Nadia Pinardi
Published: March 2021

Nature based solutions (NBSs) address key societal challenges through the protection, sustainable management and restoration of both natural and modified ecosystems. In this work we present a modeling application of this innovative approach, inspired by nature, with the goal of mitigating coastal erosion. Within the framework of the OPEn-air laboRAtories for Nature baseD solUtions to Manage environmental risks (OPERANDUM) project, the natural reserve of Bellocchio in Lido di Spina (Italy) faces frequent marine floods and intense erosive phenomena, hence being chosen as Open-Air Laboratory for the NBS implementation. The project aims to mitigate coastal erosion through the realization of an artificial sand dune made of natural materials, such as sand, wood, geotextiles and geomembranes and covered by native herbaceous and shrubby vegetation. We present the modeling activities carried out in the context of the project, aiming on the performance and efficiency evaluation  of the designed NBS, with a specific focus on the coastal morphological modelling. Thus, a numerical modeling chain has been set-up to simulate a long-term current scenario with and without the NBS. The chain is composed of the wave model WAVEWATCH III, the oceanographic model SHYFEM and the morphodynamic model XBeach for the coastal area.

XBeach was validated with available and specific (for the project) topo-bathymetric surveys of the area of interest as means to define the more accurate set-up of the model parameters. The 10 years period 2010-2019 was defined as the time range for modelling simulations. Sea level outputs from SHYFEM and wave outputs from WAVEWATCH III for the 10 years simulations are used to force the coastal model XBeach. Given the huge computational costs related to long-term simulations, an input-schematization was applied (so called “input reduction”). The approach followed for the long-term morphodynamic modelling of the NBS-XBeach setting will be shown. Moreover, the chosen coastal model domain, the model set-up and the input reduction applied will be presented.
Micromagnetic simulation of taenite particles
Authors: Devienne José , Berndt Thomas , Williams Wyn
Published: March 2021

The cloudy zone (CZ), an intergrowth structure of Fe-rich and Ni-rich phases that forms during slow cooling of iron meteorites are potential recorders of  their parent body’s thermal and magnetic history. The ability of the cloudy zone’s principal magnetic minerals, taenite and tetrataenite, to reliably record ancient magnetic fields from the early solar system has, however, insufficiently been investigated. In this work we performed a series of micromagnetic simulations in order to assess the magnetic stability of taenite grains. Micromagnetic simulations allow to investigate the changes in the magnetic state in taenite as a function of the grain size: in ellipsoidal grains below 68 nm (equivalent sphere volume diameter, ESVD) a single domain state dominates.  At 68 nm (ESVD) a “flowering” state starts, and further increase in size (> 75 nm) gives rise to a single vortex state. Contrary to common conception, theoretical evaluation of relaxation times for taenite grains based on micromagnetics leads to values that exceed the age of solar system, which makes taenite, not just its ordered equivalent tetrataenite, a reliable paleomagnetic recorder.
Bird’s eye view on steep topography
Authors: Voigtländer Anne , Tofelde Stefanie
Published: March 2021

In nadir view, normal to topography, landscapes with gentle slopes and those with steep surfaces look similar. This is due to the projection of a 3D structure onto a 2D plane. In orthophotos and digital elevation models (DEMs) topography is represented in this nadir or bird’s eye perspective. Elevation models of the Earth or planetary surfaces are often represented by gridded cells, each cell assigned with a mean elevation. In geomorphic studies, DEMs are widely used to calculate hillslope angles and surface area. Due to the projection, hillslopes at a steeper angle appear shorter and thus are represented by a smaller fraction of grid cells. Consequently, mean or median hillslope angles are distorted towards gentle slopes. This bias becomes even more obvious when comparing the projected 2D surface area versus the 3D surface area. The ratio by which a 3D surface area is underrepresented in 2D is by the cosine of the slope of the plane. Hence, the degree of area under-representation increases towards steeper slopes. At an angle of 60°, theoretically only half of the 3D surface area would be accounted for in a gridded DEM. And a hillslope at 90° is a no-show in the DEM. But already gentle slopes of 20° to 30° would be under-represented by about 10%. In addition to the under-representation of steep slopes due to the projection, DEM’s spatial resolution amplifies this bias where increasing grid size decreases the representation of steep slopes.

In essence, due to the bird’s eye view, measures of hillslope angle distribution and surface area have a bias disadvantaging steep slopes and skewing our perception towards a (flat) world of gentle slopes. Here we will discuss if and by how much this bias due to the bird’s eye view matters. First, we investigate artificial DEMs of Gaussian hills. We compare slope and surface area values using standard methods of gridded-data analysis to analytical solutions. Second, we investigate the impact of under-representation on a range of natural landscapes. This potential bias favouring gentle landscape elements has several implications for geomorphological interpretation of DEMs, including for example analyses of average erosion rates, landslide distribution or hydrological processes.
Mixture-effects on tree biomass production and soil organic C quality in a temperate plantation forest
Authors: Ahmed Iftekhar , Smith Andrew , Godbold Douglas
Published: March 2021

Forest restoration and afforestation on degraded lands are receiving tremendous research efforts globally as a climate change mitigation option. There is a growing interest in mixed species plantation to ensure sustainable ecosystem services and biodiversity. However, successful mixture of achieving these potential benefits is rare. We studied the polyculture of two pioneer fast growing species (i.e. B. pendula,  and A. glutinosa- of which A. glutinosa is N-fixing) and one shed tolerant species with slow juvenile growth (i.e. F. sylvatica) to examine the effects of species mixture on biomass production and quality of soil organic C stock following the replacement series approach. Standing woody biomass in polyculture demonstrated no over-yielding, presumably due to concurrent impacts of suppression of F sylvatica by two fast growing species and competitive reduction benefits in A. glutinosa. Similarly, standing fine root biomass production and turnover showed no significant mixture effect.  Although the quantity of soil organic C stock was unaffected by tree mixture, the vertical distribution of biodegradable C fractions was differed between mono and polyculture stands,  most probably due to slow decay rate of mixed litter. We found that species mixture decreased soil C lability in the upper soil layers, and increased recalcitrant C  in deep soil (>40 cm) that has enormous potential for long-term sequestration. We concluded that contrasting growth responses can result in no biomass over-yielding in polyculture stands but the mixed litter can affect soil C quality.

Key words: Mixture effects, Tree polyculture, biomass, over-yielding, C quality, recalcitrant C
Evaluating the influence of COVID-19 pandemic on NO2 concentration variation in selected regions in China using TROPOMI data, surface measurements and modeling approaches
Authors: Jia Zikang , Yuan Yijia , Pan Qianyu , Jin Jianbing , Gao Song
Published: March 2021

During the COVID-19 pandemic outbreak at the beginning of 2020, many Chinese urban agglomerations experienced noticeable air quality improvement. For example, recent analysis of surface measurements suggested that the concentration of NO2 decreased by on average 30% during the pandemic lockdown period in China in 2020 compared to 2019, although how much of this reduction is due to the pandemic or other factors (such as weather variation) is uncertain. We apply TROPOMI (Tropospheric Ozone Monitoring Instrument) NO2 Level 2 data (converted to Level 3 data) to analyzing the spatial and temporal evolution of NO2 in major Chinese city clusters including Jing-Jin-Ji and Yantze River Delta. These observational results are compared with monitoring station data, as well as predicted results from machine learning techniques and a chemical transport model (SILAM), taking meteorological factors into account. We then evaluate the impact of COVID-19 and lockdown measures on the concentration of NO2 comprehensively. For example, initial results indicate the NO2 concentration in Shanghai area decreased by about 37% during late January to early March in 2020, comparing the prediction by a machine learning technique (random forest) and the observed surface data, partly due to the pandemic control measures. It is expected the COVID-19 pandemic would be a long-term challenge accompanying the human development. Based on these findings, relevant mechanism of NO2 pollution and control, affected by the pandemic and periodic lockdown measures in China, will be discussed.