bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards an operationally capable satellite-based 0-100 cm soil moisture dataset from C3S
Authors: Pasik Adam , Preimesberger Wolfgang , Bauer-Marschallinger Bernhard , Dorigo Wouter
Published: March 2021

Multiple satellite-based global surface soil moisture (SSM) datasets are presently available, these however, address exclusively the top layer of the soil (0-5cm). Meanwhile, root-zone soil moisture cannot be directly quantified with remote sensing but can be estimated from SSM using a land surface model. Alternatively, soil water index (SWI; calculated from SSM as a function of time needed for infiltration) can be used as a simple approximation of root-zone conditions. SWI is a proxy for deeper layers of the soil profile which control evapotranspiration, and is hence especially important for studying hydrological processes over vegetation-covered areas and meteorological modelling.

Here we introduce the advances in our work on the first operationally capable SWI-based root-zone soil moisture dataset from C3S Soil Moisture v201912 COMBINED product, spanning the period 2002-2020. The uniqueness of this dataset lies in the fact that T-values (temporal lengths ruling the infiltration) characteristic of SWI were translated into particular soil depths making it much more intuitive, user-friendly and easily applicable. Available are volumetric soil moisture values for the top 1 m of the soil profile at 10 cm intervals, where the optimal T-value (T-best) for each soil layer is selected based on a range of correlation metrics with in situ measurements from the International Soil Moisture Network (ISMN) and the relevant soil and climatic parameters.
Additionally we present the results of an extensive global validation against in situ measurements (ISMN) as well as the results of investigations into the relationship between a range of soil and climate characteristics and the optimal T-values for particular soil depths.
On the potential of single-satellite space ties to achieve the Global Geodetic Observing System goals
Authors: Schreiner Patrick , Mammadaliyev Nicat , Glaser Susanne , König Rolf , Neumayer Karl Hans , Schuh Harald
Published: March 2021

GGOS-SIM-2, funded by the German Research Foundation (DFG), is a research collaboration project between the German Research Center for Geosciences (GFZ) and the Technische Universität Berlin (TUB). Simulations are utilized to examine the potential of co-location in space, called space ties, of the four main space geodetic techniques, i.e. DORIS, GNSS, SLR and VLBI to achieve the requirements of the Global Geodetic Observing System (GGOS) for a global terrestrial reference frame (TRF), 1 mm accuracy and 1 mm / decade long-term stability. The simulations are performed for six fictional orbit scenarios, including proposed missions GRASP (USA) and E-GRASP (EU), and expanded by a variation of the E-GRASP orbit with lower eccentricity as well as three higher orbiting circular orbits with different inclination over a time span of seven years. For most realistic simulations, we first evaluated real DORIS, GPS and SLR observations to the satellites LAGEOS 1 und 2, Ajisai, LARES, Starlette, Stella, ENVISAT, Jason 1 und 2, Sentinel 3A and B using Precise Orbit Determination (POD), to get detailed information about the individual station and receiver accuracy, availability and further technique-specific effects. Then, we generate simulated single-technique TRF solutions based on existing missions and add the co-location-in-space satellite in the six orbit scenarios. In order to quantify the effects of the different scenarios, we examine the added value w.r.t. the existing missions in terms of origin and scale and of formal errors of the station coordinates and Earth rotation parameters. We also investigate the impact of systematic errors on the derived orbits on the final TRF. The different techniques show individual advantages regarding the respective orbit parameters. For instance, a higher eccentricity of the orbit seems to lead to improved accuracy of length-of-day (LOD) from SLR. The results will help to find the best trade-off for a satellite that co-locates all four techniques in space towards a GGOS-compliant TRF and Earth rotation parameters.
The Formation of Micro-Diamonds in Decompression-Cracks During the Uplift of the Kimberlite Controlled by the C:O:H Ratio in NAMS
Authors: Sommer Holger , Jacob Dorrit , Regenauer-Lieb Klaus
Published: March 2021

We show new evidence that natural micro-diamonds can be formed in decompression-cracks by C:O:H bearing volatiles in a bimineralic eclogite. The investigated rock sample is a heterogeneous kyanite- bearing and bimineralic eclogite from the Roberts Victor mine, South Africa. Kyanite reacts out in the kyanite bearing part of the sample, but metastable relics are still present within the bimineralic part of the rock. The presence of these metastable kyanite relicts, suggest very low fH2O during the phase transition from the kyanite- bearing into the bimineralic eclogite. High-spatial-resolution synchrotron based FT-IR and RAMAN spectroscopy have been used to detect C:O:H-bearing volatiles around micro diamonds in planar defect structures in garnet in the bimineralic parts of the sample and N concentration has been analyzed within the micro-diamonds. In micro-diamond-bearing planar defect structures, a correlation between C:O:H-bearing volatiles can be identified whereas in micro-diamond -ree planar defect structures no correlation of the different C:O:H containing volatiles was detected. We suggest that the micro-diamond forming reaction was triggered by water released by the breakdown of water-bearing kyanite. We propose that the C:O:H bearing volatiles acted as a catalyst, changing in composition with changing P-T conditions in the rock during metamorphism. This catalytic process leads to permanent modification of C:O:H ratios and under favourable thermodynamic, stoichiometric and kinetic conditions micro-diamonds can be formed. Nitrogen concentrations in the analyzed micro-diamonds suggest that the formation of the micro-diamonds took place shortly before the uplift of the eclogite from the Earth mantle to the surface. The conclusions from our study proves that C:O:H-bearing volatiles, and their distribution pattern around the investigated micro-cracks, are indicative of the formation mechanisms of micro-diamonds controlled by C:O:H bearing fluids rather than by the solid-solid transformation from graphite into diamond.
Can trait-based approaches model the resilience of soil microbial communities?
Authors: Todman Lindsay , Neal Andrew
Published: March 2021

Soil microbial communities (microbiomes) are dynamic, responding continually to their surrounding environment.  These dynamics may relate to changes in the taxonomic/phylogenetic community structure as well as the functional capacity of the entire microbiome. This dynamism makes it challenging to define resilience for such ecosystems. Here, resilient communities are those able to adjust their taxonomic composition under environmental pulse or press stresses to maintain or restore a particular function.  Trait-based models typically assume trade-offs between life cycle strategies because of the resources required to enable different behaviours. An individual trait may be advantageous depending on the environmental conditions at a particular time and location. However, recent experiments addressing resilience in which soils were repeatedly exposed to stress cycles show soils developed the ability to maintain function despite a repeatedly imposed pulse stress. This suggests that a stress tolerance strategy operates in conjunction with other life cycle strategies. Here, we consider conceptual approaches to reconcile these findings – such as the inclusion of additional life strategies to represent further dimensions of soil community function and a community level trait-based approach that represents the dynamics of functional change in trait space. We also consider the challenge, pertinent to resilience modelling, of distinguishing between stress tolerance and the exposure to stress in heterogeneous soil; both aspects will affect the soil microbial community response, yet the latter could erroneously affect stress tolerance parameters in a trait-based model.
Decompacting Holocene deltas to quantify their (proper) weight
Authors: Rigoni Anita , Minderhoud Philip S. J. , Zoccarato Claudia , Teatini Pietro
Published: March 2021

Most of the world major deltas are threatened by relative sea level rise, i.e. land subsidence and sea level rise, caused by a combination of anthropogenic pressures and natural processes. This study focuses on the natural components of land subsidence directly and indirectly related to the Holocene delta stratigraphy. Firstly, subsidence is caused by natural compaction of the Holocene sediments following deposition over time under their own weight. Secondly, subsidence is caused by the visco-elastic deformation of the Earth crust driven by cumulative load of the Holocene delta (so-called Sediment Isostatic Adjustment). These two processes are obviously connected and call for a proper evaluation of the weight of (the Holocene portion of) a delta. This requires a proper quantification of specific weight and degree of compaction of Holocene deposits with depth to arrive at a first-order assessment of Holocene delta weight.

 

This study proposes an innovative methodology to address the following two questions: 1) What is the proper weight of a (Holocene) delta? 2) How much have deposits been compacted since their deposition during Holocene delta formation? Our approach integrates knowledge and data on deltaic depositional environments, stratigraphic information, geomechanical properties and other characteristics of the Holocene sequence. 

 

The developed approach is applied to eight major deltas worldwide selected from a larger database according to the availability of lithostratigraphic and geomechanical information. The analysis is conducted at the scale of an entire delta, thus required the upscaling and interpolation of datasets generally available from a few wellbores only. Lithostratigraphic data  is combined with a backwards modelling procedure to decompact the Holocene delta sequence to their decompacted thickness to provide a proper  estimation of their weight, which takes into account the (computed) in-situ compaction degree. The results show a large variability in compaction and specific weight distribution for the different deltas which underscores the substantial role of natural compaction on delta evolution. 
Geophysical study of viability for a new geomagnetic observatory at São Marcos (Portugal)
Authors: Pais M. Alexandra , Ribeiro Paulo , Pinheiro Katia , Vinicius Marcos , Matzka Juergen
Published: March 2021

The magnetic observatory of Coimbra (IAGA code COI) measures the geomagnetic field components since 1866. These long time series were disturbed by the urban expansion in Coimbra city, causing anthropogenic perturbations in particular to the high frequency spectral band of the vertical Z component.

We plan to move the observatory to another site with less magnetic disturbances. The new site is about 15 km west of Coimbra over limestone Cretaceous terrains, in São Marcos (SMC). It is far from important industrial facilities, high voltage lines, and DC electrified railways. This farm is under administration of the University of Coimbra and is surrounded by walls.  

Both magnetic surveys and electrical soundings were carried out at SMC. Results show low values for the magnetic gradients and resistivity profiles of relatively low to moderate values (~ 10-1000 ohm.m), typical of the studied lithological types (sandstone, marl and limestone). In this study we characterize the geomagnetic field as measured at SMC, in comparison with COI and SPT (San Pablo/Toledo) in Spain, the nearest observatory in the INTERMAGNET network of magnetic observatories.
Focusing of mode-2 internal solitary-like waves: an unexpected extreme internal wave
Authors: Castro-Folker Nicolas , Subich Christopher , Stastna Marek
Published: March 2021

We report on numerical simulations of stratified adjustment that yield radially propagating mode-2 waves. The initial inward propagating mode-2 wave increases in amplitude, but it does not lead to significant overturning even during the period of self-interaction near the origin. However, post-focusing, the pycnocline thins and secondary waves propagate into an environment that is very different from the undisturbed stratification. These resulting waves break, and create intrusions above and below the thinned pycnocline. While most experimental realizations of extreme internal solitary-like waves use a rectangular geometry, it should be possible to realize this situation experimentally. We discuss the resolution requirements of this situation, as well as irreversible mixing.
Cenozoic mountain building of Western Europe controlled by continental lithosphere evolution
Authors: Mouthereau Frédéric , Angrand Paul
Published: March 2021

The heterogeneous continental lithosphere of Europe inherits billion of years of tectonic evolution, mineral transformation and magmatic addition. Though there is now an extensive body of studies on the long-term geological, geochronological and geochemical evolution of the continental crust and lithospheric mantle available in Europe, yet this knowledge has not been linked to the understanding of tectonic evolution of Cenozoic Alpine mountain building. In this aim, we review geophysical, geological, petrographical, geochemical, and thermochronological constraints to infer a kinematically coherent time-integrated tectonic model for the evolution of mountain building in Western Europe, along a 4000 km long lithospheric transect from Africa to the East European Craton. We show that the key drivers of plate-scale processes related to  Alpine orogenic and topographic evolution reflect three main ingredients : 1) a protracted magmatic and tectono-thermal transformation of Africa (Gondwana) and North Europea (Baltica) cratonic mantle lithosphere since the Neoproterozoic, 2) an overall limited Mesozoic Tethyan extension of the weak Variscan lithosphere characterized by the lack of wide, thermally relaxed, oceanic lithosphere, 3) a relatively slow Cenozoic convergence between Africa and Europe, preserving initial stages of distributed tectonic inversion of rifted continental blocks throughout Europe, and partial subduction and delamination in the Mediterranean region of the most evolved lithospheric domains. 
An update to the traditional water mass (trans)formation framework.
Authors: Piracha Aqeel , Turiel Antonio , Olmedo Estrella , Portabella Marcos
Published: March 2021

Traditional estimates of convection/water mass formation at the sea surface rely on measurements of air-sea fluxes of heat and freshwater
(evaporation minus precipitation), that are estimated by combining in-situ data with meteorological modelisation. Satellite-based estimates of ocean convection are thus largely impacted by the relatively high uncertainties and low space-time resolution of those fluxes. However, direct satellite measurements of the ocean surface offer a unique opportunity to study convection (upwelling, downwelling) events with unprecedented spatio-temporal resolution compared to in-situ measurements. In this work, we propose an alternative approach to the traditional framework for estimating ocean convection using satellites. Instead of combining high-resolution ocean data of sea surface temperature and salinity with the much less precise, less resolved air-sea interaction data, we estimate the air-sea fluxes by computing the material derivatives (using satellite ocean currents) of the satellite sea surface variables. We therefore obtain estimates at the same resolution of the satellite products, and with much better accuracy than what was estimated before. We present some examples of application in the Atlantic ocean and in the Mediterranean sea. Future directions of this work is the study of the seasonal and interannual variability of ocean convection, and the potential changes on deep convection associated to climate variability at different time scales.
AMOC instability during the Last Inerglacial
Authors: Kessler Augustin , Roche Didier , Galaasen Eirik , Tjiputra Jerry , Bouttes Nathaelle , Ninnemann Ulysses
Published: March 2021

Multiple evidences from the analysis of satellite, in-situ and proxy data show that the climate is already changing toward a warmer Earth System due to our emissions of CO2 into the atmosphere. However, the magnitude and the extent of changes remain difficult to predict. A change in the ocean thermohaline circulation and its consequences for climate, such as drought, regional sea-level and ocean carbon uptake remain under debate as this circulation has been long thought to be stable during warm Earth periods – Interglacials. However, recent high-resolution reconstructions of carbon isotopes (δ13C) from the deep North Atlantic challenge this idea of stability and point toward abrupt modifications in the ocean interior biogeochemistry and/or ocean thermohaline circulation during the Last Interglacial (LIG, 125ka – 115ka).

 

Our model simulation of the LIG reproduces the observed magnitude and timescale of the reconstructed variations of δ13C, highlighting crucial dynamical changes in two regions of the North Atlantic deep-water formation (south of Greenland and south of Svalbard). These regions are found to drive the variations in the strength of the Atlantic Overturning Circulation (AMOC) when the Arctic sea-ice extent is perturbed.

 

Our study suggests that the AMOC may have experienced great instability phase during some parts of the LIG. The water mass geometry reorganization from the warm onset at 125ka to the glacial inception at 115ka could also have greatly impacted the distribution of carbon in the interior Ocean. Changes in sea-ice cover either south of Svalbard or in the Southern Ocean seem to play a determining role. However, in our global warming context, our study suggests that the mechanisms responsible for the LIG AMOC instability of the LIG may not occur by the end of the century if the Arctic sea-ice retreats from the high latitudes of the North Atlantic as projected by climate models.

 
Semi-automated assessment of geological phenomena of Active Deformation Areas (ADA) detected by radar interferometry in Alt Urgell and Cerdanya, Catalonia (Spain)
Authors: Fabregat Ivan , Casanovas Jaume , Marturià Jordi , Buxó Pere , Barra Anna
Published: March 2021

Geological hazards related to ground movements are difficult to assess at a regional scale due the lack of detailed information on the occurrence of the phenomena and the large number of potential vulnerable elements in the territory. Therefore, progress in analyzes at the regional scale can be a very useful tool for risk management.

This work, developed in the Alt Urgell and La Cerdanya counties (Catalunya, NE Spain) has served as the basis for the geological risk identification associated with ground movements. The methodology is based on the use of the Active Deformation Areas (ADA) detected by medium resolution radar satellite interferometry (Sentinel-1A and Sentinel-1B). The goal is to obtain a quick and semi-automatically classification of the ADAs according to the probable geological phenomena origin (landslides, rockfalls and subsidence).

This ADA classification is based on current data (DTM and geology) and easy to implement with GIS, takes in account: (i), landslide inventories, to allow the direct validation of the geological phenomenon; (ii) geology -information of the geological units type-; (iii) slope terrain -morphology-, determines the classification of the movement cause, depending on the slope, they are more or less prone to the generation of geological phenomena (e.g. slopes <35º: landslides); and (iv) land uses, determines the potential impact on vulnerable areas (e.g. high, in urbanized areas; low, in natural environments). This methodology provides an ADA first geological susceptibility categorization that allows optimizing and prioritizing efforts in detailed geological and geomorphological characterization works.

The clustering of scattering points gave a result of 361 ADA (over an area of around 2,000 km2), 145 was classified as potentially generated by a geological phenomenon (126 susceptible to landslides, 7 as rockfalls, 7 as subsidence and 5 as landslides or rockfalls) and 215 were classified as other causes.

Ideally, validation is based on contrasting the ADA with actual inventory data. However, the lack of complete and exhaustive inventories require validation based on classic methods such as photointerpretation and field work. All areas were checked by means of geomorphological analysis to ensure their susceptibility: 143 has identified as caused by geological phenomena, 153 has related with geological depositional process (rocky ground) and 65 has discarded.

This work has been supported by the European Commission under the Interreg V-A-POCTEFA programme (grant no. Mompa – EFA295/19).
Synergetic analyses of Earth observation time series on land surface dynamics in large river basins
Authors: Uereyen Soner , Bachofer Felix , Huth Juliane , Kuenzer Claudia
Published: March 2021

Long-term Earth observation (EO) time series are an inevitable source for past quantification and analysis as well as future forecasting of land surface dynamics. This study investigates the joint use of geoscientific time series over the last two decades, including EO-based MODIS vegetation indices, DLR Global WaterPack, DLR Global SnowPack, and DLR World Settlement Footprint as well as further climate and hydrological variables to quantify and evaluate land surface changes and their potential drivers.

For this purpose, we focus on the Indus-Ganges-Brahmaputra-Meghna (IGBM) river basin in South Asia, being the most populated and one of the most diverse river basins worldwide. In detail, it is characterized by multiple climate zones, including arid climate in the west, polar climate in the north, and tropical climate in the south east. Moreover, the northern areas of these river basins are shaped by the Himalayan mountain range, also known as the water tower of Asia, whereas the downstream areas are characterized by fertile soils and intensive agriculture in the Indo-Gangetic Plain, being dominated by extreme rainfalls during southwest summer monsoon. Here, the availability of water is of paramount importance in social, economic, as well as political terms, but threatened by climate change as well as anthropogenic pressure.

To enhance the understanding of land surface processes in the IGBM river basin, we apply state-of-the-art time series analysis techniques, including quantification and evaluation of trends and changepoints. Furthermore, we use partial correlation and a causal discovery approach to explore driving factors of land surface change. Changes and patterns are investigated with respect to the prevailing seasons over the study area. Methods were implemented with focus on spatial and temporal transferability to enable further large-scale analysis in the future. Initial results covering the last two decades over the IGBM river basin indicate an increase in greening of vegetation, mostly in areas dominated by croplands. Considering snow cover extent, we observed a decline over the Eastern Himalayas and an increase over the Western Himalayas. Moreover, changes of surface water extent are mixed over the river basin, with negative trends along the Brahmaputra and Ganges rivers and positive trends close to the Bay of Bengal. In addition, preliminary results considering linkages between EO and climate variables reveal strong partial correlation between vegetation and precipitation in western areas, whereas temperature is the dominating climate factor over eastern areas of the IGBM river basin.
Geochemical/isotope characterization of sediments from the Great Indian Desert, Thar
Authors: Bhattacharyya Rohan , Singh Satinder Pal
Published: March 2021

The Great Indian Desert, Thar is a natural source of the atmospheric mineral dust burden over India and nearby landmasses/seas and regulates the regional climate and ecosystem health. However, the limited geochemical/isotope data of Thar sediments from the source region in Rajasthan restrict their source delineation and implication for characterization of the Thar dust signatures. For this purpose, we have measured major, trace, and rare-earth elemental concentrations, and radiogenic Sr and Nd isotope compositions in 51 surface sediment samples collected over a wide area from the Thar Desert, Rajasthan. The geochemical data reveals a low degree of the chemical index of alteration (CIA ~43–54), a quartz dilution of major oxides, and depletion of heavy minerals such as zircons. The UCC normalized spider diagram, as well as La/Yb–Eu anomaly plot, reveal that the Thar surface sediments collected in this study are geochemically similar to that of a sedimentary sequence from the Luni River originating from the Aravalli mountains. The 87Sr/86Sr and εNd of Thar sediments overlap with the reported values for the Indus delta and Luni river sediments but are distinctly different from those of the Ghaggar river sediments. Thus, the sediment contribution from the Indus delta cannot be completely ruled out, while the Ghaggar sediment contributions are minimum. Furthermore, the radiogenic isotope compositions of the decarbonated Thar sediments are strikingly contrasting to the reported values for silicate fractions of eolian deposits in northwestern India. These differences could be due to grain size effects during the dust production/transport or local sediment contributions to the eolian deposits.
Lake Chala turbidites produced by surficial slope sediment remobilization: A mechanism to bring near-shore macrofossils to the deep basin with only limited time offset
Authors: Van Daele Maarten , Swai Violeth , Van der Meeren Thijs , Wolff Christian , Meyer Inka , Waldmann Nicolas , Lane Christine , De Batist Marc , Verschuren Dirk
Published: March 2021

In paleoclimate and paleoenvironmental studies, turbidites are usually considered as interruptions of the sedimentary sequence and therefore ignored. However, turbidites are composed of sediments from the (shallow) slopes along the lake’s periphery where fossil assemblages are often different to those in the deep basin. Turbidites may thus be valuable as carriers of this near-shore proxy information to a profundal core site. However, as turbidites are composed of reworked (older) sediments, their fossil content can only be exploited if their “mean time offset” can be readily estimated or ascertained to be minimal.

Several recent studies have shown that turbidites can indeed form as a result of surficial slope sediment remobilization, a process – independent of slope failure – in which only a thin veneer (20 cm) of surficial sediment is being remobilized, for example by earthquake shaking, and subsequently transported by a turbidity current. However, demonstrating that this process is active in a basin and determining the remobilization depth, is challenging, especially in the absence of slope cores. Here we study the turbidite record of the 215 m (~260 kyr) long composite core of Lake Chala in the framework of the ICDP project DeepCHALLA. We analyzed its sediment color at a 0.5-cm interval using a spectrophotometer and determined the average color for each of the 391 thickest turbidites (> 3 datapoints) in the L*a*b* color space. For the entire dataset, we performed a linear regression of the turbidite color against the average color of different intervals (2-55 cm) of laminated sediment below. For each combination of paired values, the highest R² values are found for the upper 7-15 cm of matrix sediment below the turbidites, which can thereby be interpreted as the average remobilization depth. These results are mainly based on the a* value, which shows (i) relatively poor correlations between adjacent intervals of laminated sediment (thereby not smearing the signal), and (ii) the most constant values in sediments from across the basin as determined by short-core transects. Depth-dependent variations of sediment color as determined from these transects further allows to estimate the water depth from which the turbidites were sourced.

Our results show that the sediments of most Lake Chala turbidites are 100-200 yrs older than the laminated sediments upon which they are deposited. We conclude that the turbidites can be used as ‘sampling windows’ to study temporal trends in macrofossils such as ostracods, chironomids and fish teeth, which are much more common along the basin periphery than in the deep basin.
Air quality improvements caused by COVID-19 lockdown measures in Central Europe – contributions of emission sectors and the meteorological situation
Authors: Badeke Ronny , Matthias Volker , Quante Markus , Petrik Ronny , Arndt Jan , Ramacher Martin , Schwarzkopf Daniel , Fink Lea , Feldner Josefine , Link Eliza-Maria
Published: March 2021

Corona lockdown measures caused unprecedented emission reductions in many parts of world. However, this does not linearly translate into improved air quality, since weather phenomena like precipitation, wind and solar radiation also show a significant impact on pollutant concentration patterns. The aim of this study is to disentangle effects of emission reduction and meteorology on the air quality in Central Europe during the first major lockdown from March to June 2020. For this purpose, the Community Multiscale Air Quality Modeling System (CMAQ) was used with updated emission data for the year 2020, including time profiles for sectors and countries that approximate the lockdown emission reductions. The contributions of street traffic, air traffic, ship traffic, residential heating and industry to NO2, O3 and PM2.5 concentrations were investigated. Meteorological data was derived from the regional COSMO model in CLimate Mode (COSMO-CLM). Additional city scale measurements were used to account for exceptional weather conditions as well as emission reduction effects at hotspots like traffic stations. Therefore, selected air pollutant and meteorological measurement data in the cities of Hamburg, Liége and Marseille are compared against the statistical trend of 2015 to 2019.
Ice sheet response to sub-shelf melt rates in coupled and uncoupled peri-Antarctic ice-sheet model simulations
Authors: Zipf Lars , Pelletier Charles , Haubner Konstanze , Sun Sainan , Pattyn Frank
Published: March 2021

Sub-shelf melting is the main driver of Antarctica's ice sheet mass loss. However, sub-shelf melt rate parameterizations for standalone ice models lack the capability to capture complex ocean circulation within ice shelf cavities. To overcome drawbacks of standalone models and to improve melt parameterizations, high resolution coupling of ice sheet and ocean models are capable of hindcasting past decennia and be compared to observations.

Here, we present first results of a hindcast (1985-2018) of the new circumpolar coupled Southern Ocean – Antarctic ice sheet configuration, developed within the framework of the PARAMOUR project. The configuration is based on the ocean and sea ice model NEMO3.6-LIM3 and the ice sheet model f.ETISh v1.7. The coupling routine facilitates exchange of monthly sub-shelf melt rates (from ocean to ice model) and evolving ice shelf cavity geometry (from ice to ocean model).

We investigate the impact of the coupling frequency (more precisely, the frequency of updating the ice shelf cavity geometry within the ocean model) on the sub-shelf melt rates and its feedback on the ice dynamics. We further compare the sub-shelf melt rates of the coupled setup to those of the standalone ice sheet model with different sub-shelf melt rate parametrizations (ISMIP6, plume, PICO, PICOP) and investigate the sensitivity of the response of the ice sheet for the different basal melt rate patterns on decadal time scales.
Predicting Optimal Borehole Locations for Parameter Estimation in Geothermal Reservoirs Using Optimal Experimental Design
Authors: Fink Johanna , Seidler Ralf
Published: March 2021

Drilling boreholes during exploration and development of geothermal reservoirs not only involves high cost, but also bears significant risks of failure. In geothermal reservoir engineering, techniques of optimal experimental design (OED) have the potential to improve the decision making process. Previous publications explained the formulation and implementation of this mathematical optimization problem and demonstrated its feasibility for finding borehole locations in two- and three-dimensional reservoir models that minimize the uncertainty of estimating hydraulic permeability of a model unit from temperature measurements. Subsequently, minimizing the uncertainty of the parameter estimation results in a more reliable parametrization of the reservoir simulation, improving the overall process in geothermal reservoir engineering.

Various OED techniques are implemented in the Environment for Combining Optimization and Simulation Software (EFCOSS). To address problems arising from geothermal modeling, this software framework links mathematical optimization software with SHEMAT-Suite, a geothermal simulation code for fluid flow and heat transport through porous media. This contribution shows how to determine experimental conditions such that the uncertainty when estimating different parameters of model units from temperature measurements in the borehole is minimized. Numerical simulations of synthetic geothermal reservoir scenarios are presented to demonstrate the OED workflow and its applicability to geothermal reservoir modeling
Where is the carbon going? - A multi-model comparison
Authors: O'Sullivan Michael , Friedlingstein Pierre , Sitch Stephen
Published: March 2021

Net terrestrial carbon uptake is primarily driven by increases in net primary productivity (NPP) and/or the residence time of carbon in vegetation and soil. As such, it is of critical importance to accurately quantify spatio-temporal variation in both terms and determine their drivers. Both NPP and residence times are modulated by changing environmental conditions, including climate change and variability, atmospheric CO2, and Land Use and Land Cover Changes (LULCC). For the historical period, 1901-2019, outputs from a suite of Dynamic Global Vegetation Models (DGVMs) from the TRENDY consortium, driven with observed changes in climate, CO2, and LULCC are analysed. Changes in global and regional carbon fluxes, stocks, and residence times are quantified, as well as an attribution to the underlying drivers. We find that over the historical period the majority of models simulate an increase in NPP, predominantly driven by enhanced atmospheric CO2 concentrations. This generally leads to increased carbon storage in both vegetation and soils, however there is no agreement across models on the partitioning between vegetation and soils. This increased storage also acts to reduce soil carbon residence times due to a relative increase in carbon allocated in the faster decomposing soil pools. LULCC over this period has acted to reduce carbon inputs to the system and reduce vegetation carbon residence times due to conversion of forests to shorter vegetation. We find there is a large variation in simulated global and regional fluxes, stocks, and residence times in resonse to changes in climate, implying there are considerable uncertainties in current DGVMs. We therefore use long-term global observations of productivity and biomass change to constrain model estimates and provide insight into a process attribution for biospheric change as well as highlighting areas for future model improvement.
An automatic implementation of the mixed precision in NEMO 4.2
Authors: Paronuzzi Ticco Stella Valentina , Tintó Prims Oriol , Acosta Cobos Mario , Castrillo Melguizo Miguel
Published: March 2021

At the beginning of 2021 a mixed precision version of the NEMO code was included into the official NEMO repository. The implementation followed the approach presented in Tintó et al. 2019. The proposed optimization despite being not at all trivial, is not new, and quite popular nowadays. In fact, for historical reasons many computational models over-engineer the numerical precision, which leads to an under-optimal exploitation of computational infrastructures. By solving this miss-adjustment a conspicuous payback in terms of efficiency and throughput can be gained: we are not only taking a step toward a more environmentally friendly science, sometimes we are actually pushing the horizon of experiment feasibility a little further. For being able to smoothly include the changes needed in the official release an automatic workflow has been implemented: we attempt to minimize the number of changes required and, at the same time, maximize the number of variables that can be computed using single precision. Here we present a general sketch of the tool and workflow used.
Starting from the original code, we automatically produce a new version of the same, where the user can specify the precision of each real variable therein declared. With this new executable, a numerical precision analysis can be performed: a search algorithm specially designed for this task will drive a workflow manager toward the creation of a list of variables that is safe to switch to single precision. The algorithm compares the result of each intermediate step of the workflow with reliable results from a double precision version of the same code, detecting which variables need to retain a higher accuracy.
The result of this analysis is eventually used to perform the modification needed into the code in order to produce the desired working mixed precision version, while also keeping the number of necessary changes low. Finally, the previous double precision and the new mixed precision versions will be compared, including a computational comparison and a scientific validation to prove that the new version can be used for operational configurations, without losing accuracy and increasing the computational performance dramatically.
Bayesian inference and uncertainty quantification for source reconstruction of 137Cs released during the Fukushima accident
Authors: Dumont Le Brazidec Joffrey , Bocquet Marc , Saunier Olivier , Roustan Yelva
Published: March 2021

In March 2011, large amount of radionuclides were released into the atmosphere throughout the Fukushima Daiichi nuclear disaster. This massive and very complex release, characterized by several peaks and wide temporal variability, lasted for more than three weeks and is subject to large uncertainties. The assessment of the radiological consequences due to the exposure during the emergency phase is highly dependent on the challenging estimate of the source term.

Inverse modelling techniques have proven to be efficient in assessing the source term of radionuclides. Through Bayesian inverse methods, distributions of the variables describing the release such as the duration and the magnitude as well as the observation error can be drawn in order to get a complete characterization of the source.

For complex situations involving releases from several reactors, the temporal evolution of the release may be as difficult to reconstruct as its magnitude. The source term or function of the release is described in the inverse problem as a vector of release rates. Thus, the temporal evolution of the release appears in the definition of the time steps where the release rate is considered constant. The search for the release variability therefore corresponds to the search for the number and length of these successive time steps.

In this study, we propose to tackle the Bayesian inference problem through sampling Monte Carlo Markov Chains methods (MCMC), and more precisely the Reversible-Jump MCMC algorithm.
The Reversible-Jump MCMC method is a transdimensional algorithm which allows to reconstruct the time evolution of the release and its magnitude in the same procedure.

Furthermore, to better quantify uncertainty linked to the reconstructed source term, different approaches are proposed and applied. First, we discuss how to choose the likelihood and propose several distributions. Then, different approaches to model the likelihood covariance matrix are defined.

These different methods are applied to characterize the 137Cs Fukushima source term. We present a posteriori distributions enable to assess the source term and the temporal evolution of the release, to quantify the uncertainties associated to the observations and the modelling of the problem.
On the use of Distributed Acoustic Sensing for seismic divergence and curl estimations
Authors: Edme Pascal , Paitz Patrick , Sollberger David , Kiers Tjeerd , Perron Vincent , Schmelzbach Cedric , Fichtner Andreas , Robertsson Johan O.A.
Published: March 2021

Distributed Acoustic Sensing (DAS) is becoming an established tool for seismological and geophysical applications. DAS is based on Rayleigh scattering of light pulses conveyed in fibre optic cables, enabling unprecedented strain rate measurements over kilometers with spatial resolution of less than a meter. The low cost, logistically easy deployment, and the broadband sensitivity make it a very attractive technology to investigate an increasing number of man-made or natural phenomena.

One key restriction however is that DAS collects axial strain rate instead of the vector of ground motion, resulting in a poor sensitivity to broadside events like (at the surface) vertically incident waves or surface waves impinging perpendicular to the cable. Helically wound cables partially mitigate the issue but still do not provide omni-directional response as the typical vertical component of seismometers or geophones.

The present study is about the potential of using unconventional DAS cable layouts to replace and/or complement traditional sensors. We investigate the possibility of estimating the divergence and the vertical rotational components of the wavefield from cables deployed in a square or circular shape. The impact of the size of the arrangement as well as that of the interrogation gauge length is discussed.  Real data are shown and the results suggest that DAS has the potential to offer additional seismic component(s) useful for wave type identification and separation for example.
Validation practices for satellite soil moisture retrievals: What are (the) errors?
Authors: Gruber Alexander ,   Validation Good Practice Team
Published: March 2021

In this talk, we present the results of a recently published milestone publication for the validation of global coarse-scale satellite soil moisture products (doi:10.1016/j.rse.2020.111806). It is a community effort in which validation good practice guidelineshave been developed. We provide theoretical background, a review of state-of-the-art methodologies for estimating errors in soil moisture data sets, practical recommendations on data pre-processing and presentation of statistical results, and a recommended validation protocol that is supplemented with an example validation exercise focused on microwave-based surface soil moisture products. We conclude by identifying research gaps that should be addressed in the near future. The presented guidelines are endorsed by the Land Product Validation Subgroup of the Committee on Earth Observation Satellites (https://lpvs.gsfc.nasa.gov) and aim to serve as exemplary work for the development of similar best practice guidelines in other communities.
Geotubes vs. mulching for post-fire erosion mitigation in eucalypt vs. pine plantations in Central Portugal vs. Galicia
Authors: Machado Ana Isabel , Oliveira Bruna , Serpa Dalila , Santos Martha , Jesus Fátima , Xavier Adriana , Gholamahmadi Behrouz , Martins Martinho , González-Pelayo Oscar , Keizer Jan Jacob , Consortium Life-Reforest
Published: March 2021

Wildfires are well-known to negative affect forest both directly and indirectly, due to fire-enhanced runoff generation and the associated losses of wildfire ash, soil, organic matter and nutrients. In turn, post-fire runoff and erosion can, promote eutrophication and contamination of downstream surface water bodies. A variety of erosion mitigation measures have been tested in recently burnt areas, with especially mulching with straw having been applied in operational post-fire land management in the USA and Galicia. The present work, evaluates the effectiveness of a new erosion mitigation strategy, using geotubes filled with mycotechnosols and straw, and compares it to that of mulching. This was done for the two prevalent forest types in central Portugal and Galicia, i.e. an eucalypt plantation in Central Portugal and a pine plantation in Galicia that both burnt during the summer of 2019.  Both study sites were instrumented with 9 bounded erosion plots of 16m2 with sediment traps at the bottom of the plots, divided over three blocks. The three treatments of doing nothing, mulching and geotubes were applied to one plot per block. In total, 4 geotubes were placed in each plot to create a barrier in the middle of the plot and at the bottom, just before the sediment deposition zone at the plot outlet. Mulching was done with chopped eucalypt bark at the eucalypt site and with pine needles at the pine site, at application rates of roughly 250 g m-2. Eroded sediments were collected on a bi-weekly to monthly basis, depending on occurrence of rain, during the first post-fire hydrological year. The results showed that the erosion rates of the control plots differed about one order of magnitude between the two sites, amounting to  an average of 11 Mg  ha-1 y-1 at the pine site as opposed to 1.0 Mg ha-1 y-1  at the eucalypt site. This discrepancy was probably related to soil type (derived from granite vs. schist) and stoniness. Mulching was somewhat more effective than the geotubes at the pines site, with reduction in average annual erosion rates of 84 and 77%, respectively. The opposite was true at the eucalypt site, with annual erosion reductions of on average 75 and 62%. The use of geotubes would therefore seem a further option for forest and water resources managers to decrease markedly the risks of both elevated and reduced soil (fertility) losses from recently burnt hillslopes and the associated risks for downstream values.
Susceptibility of glacial lakes to avalanche and rockfall in the Hindu-Kush-Himalaya
Authors: Dubey Saket , Goyal Manish , Sattar Ashim , Haritashya Umesh
Published: March 2021

The Hindu-Kush-Himalayan region is home to numerous glacial lakes. Some of these lakes could fail and produce hazardous Glacial Lake Outburst Floods (GLOF). GLOFs are primarily triggered by an avalanche or a rockfall entering the lake that generates an overtopping displacement waves. In the present study, we investigate the susceptibility of all lakes present in the Hindu-Kush-Karakorum (HKH) region (Randolph Glacier inventory region 14 and 15) to the dynamic mass movement (avalanche and rockfall). Avalanche and rockfall trajectories are developed considering various depths and “Minimum Look-Up Angle” (MLUA: a term used to define the avalanche runout distance). These trajectories are also validated against the results obtained from the Rapid Mass Movement Simulation (RAMMS) model. The mass movement of avalanche or rockfall along the major axis may enhance the wave run-up leading to a higher impact on the damming structure. Therefore, each susceptible lake is critically assessed for the angle of intrusion of a mass movement. The stability of the glacial lakes was also evaluated using the steep lake front area method to understand the associated hazard. Obtained results suggest that out of 3725 glacial lakes, 239 are susceptible to an avalanche when the mean avalanche depth is considered 50 m, and only 43 if the assumed mean avalanche depth is reduced to 10 m. Furthermore, the rockfall trajectories suggest that 343 lakes are susceptible to rockfall while considering MLUA of 17˚, which falls to 217 when MLUA is increased to 23˚. Overall, glacial lakes in the Central Himalayas were more susceptible to mass movement than the Karakoram, Western and Eastern Himalayas. We hope that our work will enable stakeholders to make a well-informed decision for hazard management in the Hindu-Kush-Himalayas. In addition to this, developed avalanche and rockfall trajectories will also help identify critical regions and hazard susceptibility structures.