bluuebunny/crossref_metadata_2025 huggingface dataset:
Floodplains representation in Land Surface Model : toward higher resolution
Authors: Schrapffer Anthony , Polcher Jan , Sörensson Anna , Fita Lluis
Published: March 2021

Floodplains are flat regions close to rivers which are temporarily or permanently flooded. When they are next to large streamflow, their flooding is mainly related to the river overflow and, thus, to the precipitation occurring in the upstream regions. Large floodplains are important for the regional water cycle, the hydrological resources, the ecological services they provide and, when they are located in tropical regions, for their interaction with the atmosphere. Large tropical floodplains exist in the Amazon, the Mississippi, the Congo, the Paraguay and the Nile basins. 

On the one hand, floodplains are regions with scarce ground observations which lead to difficulties to assess the accuracy of the satellite products that limits their calibration. One the other hand, the dynamic of the floodplains is usually not integrated in Land Surface Models and even less in Earth System Models although they may be important for land-atmosphere interactions. There is a need to develop numerical schemes in order to be able to represent the impact of the floodplains on the water cycle. These schemes will also allow us to better understand the hydrological dynamics in these regions. 

The Land Surface component of the IPSL Earth System Model, ORCHIDEE (CMIP6 version) includes a river routing scheme with a floodplains scheme at a resolution of 0.5°. This scheme allows the water from the precipitation over the upstream region to flood and evaporate over the floodplains. Recent developments in ORCHIDEE driven by the need for a higher resolution routing scheme, based on sub-grid hydrological units, allowed us to implement a floodplain scheme which improves the representation of the overbank flow and the spatial distribution of ponded water with respect to the CMIP6 version of ORCHIDEE. 

This study focuses on the Pantanal region which is the world’s largest tropical floodplains and is located in the La Plata Basin, in the Upper Paraguay River (South America). ORCHIDEE’s sensitivity to the activation of floodplain schemes has been assessed through simulations performed at various resolutions. These simulations have shown the importance of representing floodplains to simulate the water cycle in the area. Combining these simulations and observations, we estimated the evapotranspiration loss by models when the floodplains scheme is deactivated to 90 mm/year over the Pantanal. The higher resolution scheme shows realistic simulations of the river discharge over the floodplains and is expected to improve the spatial distribution of the flooded area and, thus, the representation of evapotranspiration.
What’s the impact of improved soil representations in the ECMWF land surface model and how does it affect the extremes?
Authors: Boussetta Souhail , Arduini Gabriele , Balsamo Gianpaolo , Dutra Emanuel , Agusti-Panareda Anna , Zoster Ervin , Stevens David
Published: March 2021

With increasingly higher spatial resolution and a broader applications, the importance of soil representation (e.g. soil depth, vertical discretisation, vegetation rooting) within land surface models is enhanced. Those modelling choices actually affects the way land surfaces store and regulate water, energy and also carbon fluxes. Heat and water vapour fluxes towards the atmosphere and deeper soil, exhibit variations spanning a range of time scales from minutes to months in the coupled land-atmosphere system. This is further modulated by the vertical roots' distribution, and soil moisture stress function, which control evapotranspiration under soil moisture stress conditions. Currently in the ECMWF land Surface Scheme the soil column is represented by a fixed 4 layers configuration with a total of approximately 3m depth.

In the present study we explore new configurations with increased soil depth (up to 8m) and higher vertical discretisation (up to 10 layers) including a dissociation between the treatment of water and heat fluxes. Associated with the soil vertical resolution, the vertical distribution of roots is also investigated. A new scheme that assumes a uniform root distribution with an associated maximum rooting depth is explored. The impact of these new configurations is assessed through surface offline simulations driven by the ERA5 meteorological forcing against in-situ and global products of energy, water and carbon fluxes with a particular focus on the diurnal cycle and extreme events in recent years.
A new GLOF inventory for the Peruvian and Bolivian Andes
Authors: Emmer Adam , Cook Simon , Wood Joanne L. , Harrison Stephan , Wilson Ryan , Diaz-Moreno Alejandro , Reynolds John M. , Torres Juan
Published: March 2021

Addressing the question of whether Glacial Lake Outburst Floods (GLOFs) are changing in frequency and magnitude in modern times requires historical context, but suffers from incomplete GLOF inventories, especially in remote mountain regions. Here, we exploit high-resolution, multi-temporal satellite and aerial imagery combined with documentary data to identify GLOF events across the glacierized Cordilleras of Peru and Bolivia, using a set of diagnostic geomorphic features. More than 150 GLOFs are characterised and analysed, far exceeding the number of previously reported events. We provide statistics on location, magnitude, timing and characteristics of these events. Further, we describe several cases in detail and document a wide range of process chains associated with GLOFs. Our findings outline implications for regional GLOF hazard identification and assessment and provide solid basis for enhanced understanding GLOF occurrence under changing climate conditions and glacier retreat.
Evolution of tracer and ice crystal distribution in the young plumes of overshooting turrets from the StratoClim golden flight 
Authors: Khaykin Sergey , Krämer Martina , Moyer Elizabeth , Bucci Silvia , Afchine Armin , Borrmann Stephan , Cairo Francesco , Clouser Benjamin , D’Amato Francesco , Legras Bernard , Lykov Alexey , Mitev Valentin , Matthey Renaud , Rolf Christian , Singer Clare , Ulanovsky Alexey , Viciani Silvia , Volk Michael , Yushkov Vladimir , Stroh Fred
Published: March 2021

Deployment of the high-altitude M55-Geophysica aircraft in Kathmandu during Summer 2017 within StratoClim campaign has yielded a wealth of unique high-resolution measurements in the Asian Monsoon Anticyclone (AMA). In a particular flight (F8, 10 August 2017) the aircraft flew at the cold-point tropopause level through active overshoots and their outflows minutes to hours old. The measurements reveal up to 2500 ppmv of ice water above 17 km in large aggregated ice crystals up to 700 µm in diameter. Smaller crystals were observed as high as 18.8 km (410 K). Tracer and thermodynamical measurements show manifestations of vigorous vertical motions and provide evidence for ongoing mixing of tropospheric and stratospheric air around the tropopause. We use an ensemble of airborne and satellite measurements inside and downwind of convective overshoots together with trajectory modeling to characterize the impact of overshooting convection on the thermodynamical structure and chemical composition of the Asian tropopause layer. The effect of cross-tropopause convective transport on the Asian lower stratospheric water vapour is discussed.
Imaging the rupture zone of the 1912 Ganos earthquake using fault zone head waves from a local seismic network
Authors: Gorgun Burcak , Yalcinkaya Esref , Gorgun Ethem , Bohnhoff Marco , Alp Hakan
Published: March 2021

The Ganos Fault (GF) is the westernmost onshore segment of the North Anatolian Fault Zone (NAFZ) and was last activated in the Mw7.4 Ganos/Mürefte earthquake in 1912. The GF is a first order linear and a right lateral strike-slip fault with a locking depth of 8-17 km. A 40-station seismic array has been deployed between 2017 and 2020 along the GF to study the fault zone characteristics at depth. Fault Zone Head Waves (FZHW) are an important diagnostic signal to detect velocity contrast across fault and thus identify them as interfaces. A fault consisting of a sharp material contrast between different lithologies is expected to generate FZHW. They spend a large portion of their propagation paths refracting along the bimaterial interface. The head waves propagate with the velocity and motion polarity of the faster block, and are radiated from the fault to the slower velocity block where they are characterized by an emergent waveform with opposite motion polarity to that of the direct body waves. The FZHW are the first arriving phases at locations on the slower block with normal distance to the fault less than a critical distance. The high station coverage across the fault will allow us to observe micro-earthquake activity and FZHW close to the seismically active region of the GF throughout the entire seismogenic depth down to approximately 20 km thereby enhancing the resolution of seismological observations in that area. Preliminary results from MONGAN array allow to identify FZHWs at several stations in waveforms originating from events in the western Marmara Sea. We focus on the interpretation of a distinct first phase (FZHW) contained in the waveform coda that is well separated from the direct P wave. FZHWs are visible in many waveforms and have a specific time delay before the direct P wave arrivals at each station. Based on a polarization analysis of records at MONGAN stations, this first phase is interpreted as a FZHW at an interface near the study area. Its particle motion is consistent with FZHW and the direct P wave produced by the bimaterial interface. This is an indication of a bimaterial interface along the GF where the northern block is faster than the southern block.
Recalculations between different expressions of stable HCNOS isotope results – is it easy?
Authors: Skrzypek Grzegorz , Dunn Philip
Published: March 2021

The stable HCNOS isotope compositions can be reported in various ways depending on scientific domain and needs. The most common notations are 1) the isotope ratio of two stable isotopes; 2) isotope delta value, and 3) atom fraction of one or more of the isotopes. Frequently recalculations between these notations are required for certain applications, particularly when merging different data sets. All these recalculations require using the absolute isotope ratio for the zero points of the stable isotope delta scales (Rstd). However, several Rstd with very contrasting values have been proposed over time and there is no common agreement on which values should be used word-wide (Skrzypek and Dunn, 2020a).

Differences in the selection of Rstdvalue may lead to significant differences between different data sets recalculated from delta value to other notations. These differences in Rstd have a significant influence also on the normalization of raw values but only when the normalization is conducted versus the working standard gas value. We proposed a user-friendly EasyIsoCalculator (http://easyisocalculator.gskrzypek.com) that allows recalculation between the main expressions of isotope compositions using various Rstd and aids for identification of potential inconsistencies in recalculations (Skrzypek and Dunn, 2020b).

 

Skrzypek G., Dunn P. 2020a. Absolute isotope ratios defining isotope scales used in isotope ratio mass spectrometers and optical isotope instruments. Rapid Communications in Mass Spectrometry 34: e8890.

Skrzypek G., Dunn P., 2020b. The recalculation of the stable isotope expressions for HCNOS – EasyIsoCalculator. Rapid Communications in Mass Spectrometry 34: e8892.
Astrochronology for the oldest Cambrian trilobites in Moroccan West Gondwana
Authors: Sinnesael Matthias , Millard Andrew R. , Smith Martin R.
Published: March 2021

The lower Cambrian successions of Southern Morocco (West Gondwana) feature some of the oldest trilobites and archaeocyaths fossil remains in the world, as well as some of the largest carbon isotope excursions of the Phanerozoic. Combined with multiple state-of-the-art U-Pb radio-isotopic constraints, these sections are key references for lower Cambrian stratigraphy. We suggest that some of the regularly alternating lithological sequences, which show various orders of nested cyclicity, carry a signal of astronomical climate forcing. In agreement with a U-Pb Bayesian age model, the primary lithological alternation corresponds with the precession astronomical cycle while clear amplitude modulation patterns reflect a short-term eccentricity imprint. Both small- and large-scale features are laterally continuous at great distances. Changes in lithology may have been primary controlled by changes in terrigenous input. This integrated astrochronological age model has the potential to result in unprecedented early Cambrian timescales for major paleoenvironmental changes like the appearance of key fossils and large carbon isotope excursions. Often, lower Cambrian and Precambrian strata lack classical stratigraphical tools like good index fossils or magnetostratigraphy. In comparison with younger strata, the combined use of high-quality radio-isotopic dating and high-precision astrochronology might be even more crucial to disentangle important events in the early evolution of life and climate on our planet.
The role of nearshore currents in limiting coastal dispersal
Authors: Ward Sophie , Robins Peter , Jenkins Stuart
Published: March 2021

The introduction, spread and establishment of marine non-native species, facilitated by species’ dispersal capabilities and enhanced by the continued expansion of global trade and transportation networks, presents a global threat to marine biodiversity and ecosystem functioning. Increases in hard structures such as offshore renewable energy devices or coastal defenses, built partly as a response to climate change, potentially facilitate the secondary spread of non-native species by providing stepping stones of suitable habitat for fouling organisms. Within the ECOSTRUCTURE project we are developing biophysical modelling techniques to help predict and understand the dispersal of marine organisms in the Irish Sea. However, shelf-scale biophysical models typically omit near-shore and inter-tidal features and processes, which potentially play a significant role in larval dispersal. Here, we evaluate how nearshore flows affect coastal larval spread in the Irish Sea, a semi-enclosed energetic shelf sea with considerable potential for renewable energy developments as well as with evidence of existing marine non-native communities. We use an unstructured, finite element, hydrodynamic model of a topographically-complex coastline (which includes headlands, bays and channels) at four different spatial scales (50 – 500 m) to compare the influence of model spatial resolution on transport and dispersal patterns of particles released within the nearshore region. We found that particles were transported offshore more quickly and travelled further overall in the relatively higher-resolution simulations. The lower-resolution simulations appeared to be more retentive in the nearshore zone, resulting in increased alongshore connectivity. With a better understanding of the role of nearshore dynamics on larval transport processes, it is possible to more accurately simulate the spread of non-native species in the marine environment.
The Home River Bioblitz: A World-Wide Collaboration Between Citizens to Show the Importance of Free-Flowing Rivers
Authors: Droujko Jessica , Velazco-Macías Carlos , Faro David , Benöhr Jens , Knook Vera , Virik Kara Lena
Published: March 2021

One challenge in collaborating with citizen scientists is to keep them motivated to continuously collect data in the long-term. The Home River Bioblitz event overcomes this roadblock by engaging hundreds of citizens around the world in one single day. In general, a bioblitz is a communal citizen-science effort to record a wide variety of species at a specific location within a certain timeframe. This single-day commitment enables large-spatial resolution data to be collected. The Home River Bioblitz was created by the River Collective, National Geographic, Bestias del sur Salvaje, and iNaturalist as part of the citizen science program supported by the National Geographic Society. The first event took place on September 20th, 2020 on 43 rivers located in 24 countries around the world. Over 500 participants from five continents used the iNaturalist app to log 5245 observations and 1772 species of flora and fauna, with at least 14 species under IUCN status, contributing to the Global Biodiversity Information Facility repository. This method of low-temporal and high-spatial data collection is used to identify new species, IUCN red list species, local endemic species, and invasive species. Not only does this event engage citizen-scientists to contribute to biodiversity findings, but it also connects people to their local environments by having them zoom into details they normally pass by. By celebrating the diversity of rivers and meeting the people around them, we were able to bring communities closer to knowing the species of their local rivers and raise awareness about the importance of free-flowing and healthy rivers around the world. An online post-event was dedicated to sharing these local river species and the scientific impact of certain observations with the participants. This event also opens up the possibility to collect other types of short term, large-spatial data around river ecosystems. In the next edition of the Home River Bioblitz, we would like to encourage the participants to collect hydro-morphological and water quality data by using open-access and low-cost citizen science tools, such as the Discharge app and the Waterrangers kit. The Home River Bioblitz event will not only be used to engage and educate participants on their local rivers, but the biodiversity and potentially chemico-physical and hydro-morphological data that will be collected could serve to develop time-series to help assess temporal variations and stressors.
Atlantic Water Modification North of Svalbard in the Mercator Physical System From 2007 to 2020 
Authors: Provost Christine , Athanase Marylou , Pérez-Hernández Maria-Dolores , Sennéchael Nathalie , Bertosio Cécilia , Artana Camila , Garric Gilles , Lellouche Jean-Michel
Published: March 2021

The Atlantic Water (AW) inflow through Fram Strait, largest oceanic heat source to the Arctic Ocean, undergoes substantial modifications in the Western Nansen Basin (WNB). Evaluation of the Mercator system in the WNB, using 1,500 independent temperature‐salinity profiles and five years of mooring data, highlighted its performance in representing realistic AW inflow and hydrographic properties. In particular, favorable comparisons with mooring time‐series documenting deep winter mixed layers and changes in AW properties led us to examine winter conditions in the WNB over the 2007–2020 period. The model helped describe the interannual variations of winter mixed layers and documented several processes at stake in modifying AW beyond winter convection: trough outflows and lateral exchange through vigorous eddies. Recently modified AW, either via local convection or trough outflows, were identified as homogeneous layers of low buoyancy frequency. Over the 2007–2020 period, two winters stood out with extreme deep mixed layers in areas that used to be ice‐covered: 2017/18 over the northern Yermak Plateau‐Sofia Deep; 2012/13 on the continental slope northeast of Svalbard with the coldest and freshest modified AW of the 12‐year time series. The northern Yermak Plateau‐Sofia Deep and continental slope areas became “Marginal Convection Zones” in 2011 with, from then on, occasionally ice‐free conditions, 50‐m‐ocean temperatures always above 0 °C and highly variable mixed layer depths and ocean‐to‐atmosphere heat fluxes. In the WNB where observations require considerable efforts and resources, the Mercator system proved to be a good tool to assess Atlantic Water modifications in winter.
Carbon distribution between density and particle size classes of differently managed soils in a 40-year agronomic long-term trial
Authors: Mayer Marius , Fliessbach Andreas , Mäder Paul , Steffens Markus
Published: March 2021

Soils contain more carbon (C) in the form of organic matter (soil organic matter = SOM) than the entire atmosphere and global vegetation combined. They are a central component of the global C cycle and its largest dynamic reservoir. Smart agricultural practices are discussed, on the one hand, as a way to mitigate climate change because they can increase the amount of SOM and thus actively remove C from the atmosphere. On the other hand, all intensively used soils lose C in the long term. The scientific key questions in this context revolve around the extent and dynamics of C storage, as well as the associated stabilization mechanisms involved and effects of agricultural use on the C budget.

The DOK experiment is a long-term agronomic field trial near Basel (Switzerland) that compares biodynamic, organic and conventional management systems since 40 years. Within the "DynaCarb" project, we investigate how the management systems affect SOM fractions during the 40-year experimental period. We compare the unfertilized control to a purely mineral, a purely organic, and a combined fertilized, mineral-organic variant (four field replicates each) during six crop rotation cycles. By using a combined density and particle size fractionation, the SOM is separated into particulate and mineral-associated fractions and their development is quantitatively investigated in archived samples from 1982, 1989, 1996, 2003, 2010, and 2017.

"DynaCarb" investigates the medium- and long-term effects of different agricultural systems on SOM. These results are of great importance for the evaluation of the C sequestration potential of agricultural soils and for the identification of suitable management and fertilization strategies.
Spatial and temporal simulation of groundwater recharge amount and cross-validation with point measurement-based estimations on a tropical basin comprising volcanic aquifers: case study of Lake Tana basin, northwestern Ethiopia
Authors: Yenehun Alemu , Dessie Mekete , Nigate Fenta , Belay Ashebir Sewale , Azeze Mulugeta , Van Camp Marc , Fentie Derbew , Kidane Desale , Van Griensven Ann , Adgo Enyew , Nyssen Jan , Walraevens Kristine
Published: March 2021

A physically distributed water balance model called WetSpass is applied to estimate the recharge for the semi-humid Lake Tana basin in northwest Ethiopia. Lake Tana basin, one of the major sub-basins of the Upper Blue Nile River basin, covers 15,077 km2 of which 3,156km2 is the lake water body. The basin is regarded as one of the growth corridors of the country, where huge waterworks infrastructure is being developed. The basin has complex volcanic aquifer systems due to the multi-stage volcanism of the Cenozoic and Quaternary eras comprising many dikes, extended volcanic necks, and centers. Hence, estimating hydrological terms such as groundwater recharge considering the high basin physical heterogeneities is difficult, though highly important. In this study, the WetSpass model is developed, and recharge surface, surface runoff, and evapotranspiration at 90 m grid resolution have been developed. The spatial recharge map is cross-validated with water table fluctuation (WTF) and chloride mass balance (CMB) methods. The mean annual recharge, surface runoff, and evapotranspiration over the whole basin using WetSpass are estimated at 315 mm, 416 mm, and 770 mm, respectively. The mean annual recharge ranges from 0 mm to 1085 mm: 0 mm at water bodies and highest on highly fractured Quaternary basalt. Similarly, a high range of recharge is also noted using WTF and CMB methods showing the strongly heterogeneous nature of the hydro(meteoro)logical characteristics of the area. Generally, the recharge is found higher in the southern and eastern catchments and lower in the northern catchments, primarily due to higher rainfall amounts and highly permeable geological formations in the former parts. A fair general correlation between the recharge by WTF and WetSpass is found. However, WetSpass is more effective in the highland areas where the recharge is controlled by rainfall, while the WTF method is more effective in the storage controlled flat floodplain area. CMB is applied in a less spatially distributed way, and hence, the spatial performance of the method is not well evaluated. However, logged water infiltration in the floodplains, and transpiration from the groundwater in shallow water table areas have disturbed the estimated recharge by the CMB method. The land-use change from 1986-2014 brought relatively small hydrological change, although the land use has changed significantly.
Life cycle assessment of geothermal power generation in the Southern German Molasse Basin – The binary plant Kirchstockach
Authors: Bott Christoph , Menberg Kathrin , Heberle Florian , Brüggemann Dieter , Bayer Peter
Published: March 2021

Under geologically beneficial conditions, geothermal facilities are often rated as efficient, as well as clean and climate-neutral energy technologies. In fact, for supporting a good environmental performance of a technology, the total environmental impact caused by all associated material and energy consumption needs to be examined. Life cycle assessment (LCA) according to ISO standards 14040 and 14044 considers not only operation, but also the construction and decommissioning phases while addressing different environmental impact categories. Therefore, LCA-based environmental evaluation has been proposed in several previous studies. A review of the state-of the art in this field shows that some critical system parameters are often disregarded. Furthermore, many existing studies are solely based on theoretical datasets without validation to specific application cases.

Our work addresses these two shortcomings by performing a comprehensive LCA using operational data of the binary, two-stage ORC, Kirchstockach power plant in the Southern German Molasse Basin. Given its technical specifications, a representative base case scenario provides an excellent reference for benchmarking against other power plants. Environmental impacts of different technical modifications are assessed in terms of global warming potential, non-renewable energy consumption, aquatic acidification and eutrophication. Using scenario analyses, we consider the influence of emerging key factors, such as refrigerant leakage, focusing on various system components. Firstly, we identify reinforcing effects due to interrelationships between these system parameters, e.g. when using environmentally friendly ORC refrigerants. Secondly, uncertainty analyses provide insights into potential measures for ecological system improvements by using different materials and methods in the construction and operation phases. For comparison and benchmarking purposes, conventional power generation resources and comparable studies in the field of binary geothermal systems, enhanced geothermal systems, and flash systems are included. Besides the general positive ranking of the Kirchstockach power plant environmental performance, our multi-objective study ultimately reveals not only key performance factors, but it also underlines the overall relevance of case studies to validate generic and global assumptions.
A new 3-D mantle density model from recent normal-mode measurements
Authors: van Tent Rûna , Deuss Arwen , Fichtner Andreas , Gebraad Lars , Schneider Simon , Trampert Jeannot
Published: March 2021

Constraints on the 3-D density structure of Earth’s mantle provide important insights into the nature of seismically observed features, such as the Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle under Africa and the Pacific. The only seismic data directly sensitive to density variations throughout the entire mantle are normal modes: whole Earth oscillations that are induced by large earthquakes (Mw > 7.5). However, their sensitivity to density is weak compared to the sensitivity to velocity and different studies have presented conflicting density models of the lower mantle. For example, Ishii & Tromp (1999) and Trampert et al. (2004) have found that the LLSVPs have a larger density than the surrounding mantle, while Koelemeijer et al. (2017) used additional Stoneley-mode observations, which are particularly sensitive to the core-mantle boundary region, to show that the LLSVPs have a lower density. Recently, Lau et al. (2017) have used tidal tomography to show that Earth's body tides prefer dense LLSVPs.

A large number of new normal-mode splitting function measurements has become available since the last density models of the entire mantle were published. Here, we show the models from our inversion of these recent data and compare our results to previous studies. We find areas of high as well as low density at the base of the LLSVPs and we find that inside the LLSVPs density varies on a smaller scale than velocity, indicating the presence of compositionally distinct material. In fact, we find low correlations between the density and velocity structure throughout the entire mantle, revealing that compositional variations are required at all depths inside the mantle.
 Numerical tools to model seismic waves in unconsolidated and partially saturated granular media
Authors: Asfour Kassem , Martin Roland , Bodet Ludovic , El Baz Didier , Plazolles Bastien , Abreu-Torres Javier
Published: March 2021

In order to accurately study the properties of partially saturated unconsolidated media at the near surface scale, or be able to image deeper structures through them, accurate 2D and 3D wave propagation numerical modelling tools are required. The rheology/mechanical properties of such media are frequently extremely complex (nonlinear, anisotropic, ... ), even when considered at dry state and of homogeneous mixture. Experimental observations (both at the laboratory and field scales) show that the seismic wave-field in unconsolidated granular materials remains difficult to interpret within standard methodological frameworks. We present here a numerical study aiming at exploring possible alternative forward modelling approaches to better extract information from recorded signals.

 

We first present a finite volume method (Asfour et al. 2021) in which exact Riemann solvers are introduced. Solutions are compared to high-order finite-differences (Seismic_CPML code) and spectral finite element (SPECFEM code) solutions. A first series of synthetic cases is shown to benchmark the code at the hundred meters scale with a 100-300Hz wavelet source content. Another synthetic and more reallistic case is then presented with a medium affected by a steep nonlinear velocity gradient in depth, typical of an unconsolidated granular medium (as previously considered  at laboratory scale). For this model, a 1500Hz dominant frequency point source wavelet is considered and fluid saturation is also tested by applying a fluid-solid coupling. First arrival times and PSV-wave dispersion obtained from the different codes are compared.

 

In a second step, and considering the real data recorded at the laboratory, we apply a more realistic source wavelet (obtained through signal spectrum ratio) and we perform parallelized high-order finite difference simulations (UNISOLVER code) to compare 2D and 3D elastic as well as poroelastic solutions on finely discretized meshes. Computed and observed data are compared. The poroelastic rheology provides better amplitudes in the seismograms and better exhibits some PSV modes in the phase velocity dispersion observations. Sensitivity kernels are also shown for the different rheologies. The different results obtained are now paving the way to seismic inversion at the near surface scale and to image shallow fluid/water saturated layers.
Sea ice fragmentation and its role in the evolution of the Arctic sea ice cover. 
Authors: Bateson Adam , Feltham Daniel , Schröder David , Wang Yanan , Hwang Byongjun , Ridley Jeff , Aksenov Yevgeny
Published: March 2021

The Arctic sea ice cover is not a continuous expanse of ice but is instead composed of individual sea ice floes. These floes can range in size from just a few metres to tens of kilometres. Floe size can influence a variety of processes, including lateral melt rates, momentum transfer within the sea ice-ocean-atmosphere system, surface moisture flux, and sea ice rheology. Sea ice models have traditionally defined floe size using a single parameter, if floe size is explicitly treated at all. There have been several recent efforts to incorporate models of the Floe Size Distribution (FSD) into sea ice models in order to explore both how the shape of the FSD emerges and evolves and its impact on the sea ice cover, including the seasonal retreat. Existing models have generally focused on ocean surface wave-floe interactions and thermodynamic melting and growth processes. However, in-situ observations have indicated the presence of mechanisms other than wave fracture involved in the fragmentation of floes, including brittle failure and melt-induced break up.

In this study we consider two alternative FSD models within the CICE sea ice model: the first assumes the FSD follows a power law with a fixed exponent, with parameterisations of individual processes characterised using a variable FSD tracer; the second uses a prognostic approach, with the shape of the FSD an emergent characteristic of the model rather than imposed. We firstly use case studies to understand how similarities and differences in the impacts of the two FSD models on the sea ice emerge, including the different spatial and temporal variability of these impacts. We also consider whether the inclusion of FSD processes in sea ice models can enhance seasonal predictability. We will also demonstrate the need to include in-plane brittle fracture processes in FSD models and discuss the requirements needed within any parameterisation of the brittle failure mechanism.
Studying bedrock fracture and weathering patterns with cosmic-ray induced muon particles
Authors: Holma Marko , Sarala Pertti , Hall Adrian M. , Kuusiniemi Pasi , Tanaka Hiroyuki K.M. , Varga Deszo
Published: March 2021

Subsurface fracturing and weathering in bedrock are typically studied and imaged with conventional remote geophysical techniques. We introduce a new technique, muography, for carrying out such studies. This technique is based on the detection of atmospheric cosmic-ray induced muon particles after they pass through rock. The method plots the attenuation of muon flux in materials of different thickness and density (simply, dense materials “stop” more muons). The raw muon flux is translated into 2D images and 3D models showing variations in mean densities in a visually meaningful manner. As a rule of thumb, a 1% density difference between two rock bodies yields approximately 3% difference in the respective muon fluxes. The muographic density maps cover the Volume of Interest (VOI) that is located between the muon detector(s) and the source of muons (sky). Hence, the detector must be installed behind the VOI. Appropriate settings for muography include the sides of mountains, hills, cliffs and gorges, and in tunnels or boreholes below the ground surface.

Muography provides an interesting new opportunity to study and remotely image subsurface fracturing and weathering. Understanding fracturing and weathering is important as they control, for example, erosion, soil formation, the stability of rock and soil slopes, and stability of tunnels. Weathering also has a link to past climates, palaeogeographic reconstructions, and natural geochemical cycles. Weathered bedrock is also a target for mineral exploration. Due to these reasons, we are planning field surveys in northern Finland. These surveys are also used for fine-tuning the muon detector’s operational parameters and to improve its current design to cope with operating conditions in the Arctic. The survey area around Vuotso lies within the ice-divide zone of the Fennoscandian ice sheet, a zone of low glacial erosion through the Pleistocene. We have identified two survey targets: (i) a tor-studded granite dome at Riestovaara, with extensive granite outcrops that show curved sheet joints and (ii) Mäkärä, a rare-earth mineral prospect in the Tana Belt where amphibolites and garnet–biotite gneisses are covered by thick kaolinitic saprolites of pre-Pleistocene age and overlain by clay-rich till enriched in La and Y. Reconnaissance muon surveys across these contrasting terrains can be calibrated against a wealth of existing GTK data from field mapping and boreholes. The muon survey aims to provide important new subsurface information on fracture patterns at depth on the Riestovaara dome and on deep weathering patterns at Mäkärä. Muography has potential to become a fundamental tool for low-cost subsurface surveying, with applications in geomorphology, mineral exploration, and civil and mining engineering.
Relating spatial-temporal b-value patterns of induced earthquakes of the Groningen gas field to differential stress changes due to reservoir extraction
Authors: Güdük Nilgün , Muntendam-Bos Annemarie , Jansen Jan Dirk
Published: March 2021

The Gutenberg-Richter law describes the frequency-magnitude distribution of seismic events where its slope, the 'b-value', is commonly used to describe the relative occurrence of large and small events. Statistically significant b-value variations have been measured in laboratory experiments, mines, and various tectonic regimes (Wiemer & Wyss, 2002). An inversely proportional dependency of the b-value on the differential stress has been observed across different scales (Amitrano, 2003; Schorlemmer et al., 2005). Layland-Bachmann et al. (2012) have shown that this could explain the observed pattern of induced seismicity spatial-temporal b-value variations in Enhanced Geothermal Systems. In our study, we look for a similar relation applied to the Groningen gas field in the Netherlands.

It is well known that the poroelastic changes in differential stress during gas extraction are influenced by the offset of the reservoir layer across the fault. Recently, Jansen et al. (2019) and Lehner (2019) proposed an analytical solution for stress changes on offset faults due to reservoir depletion. In a parallel study, we extended this solution to include the development of aseismic slip under slip weakening and the derivation of the onset of seismic slip.
We utilize this formulation to derive the onset of seismic slip on theoretical faults of variable fault offset, dip, and reservoir thickness. Subsequently, we map our theoretical faults onto the pre-existing faults in the Groningen gas field, deriving fault segment-specific depletion levels at which the segment would become seismically active. We then simulate reservoir depletion conditions over time and assign an event magnitude to fault segments that move past their seismic activation depletion. To assign a magnitude, we use the observation that b-values are inversely proportional to differential stress, which is governed by the pore pressure depletion. Hence, we assume a simple inverse linear relation with pore pressure depletion. Each event magnitude is then randomly drawn from the probability density function of the Gutenberg-Richter distribution with the b-value assigned.
We aim to compare the obtained catalogue and its b-value distribution both in time and space to the observed event-size distribution of the Groningen gas field as derived by Muntendam-Bos and Güdük (EGU abstract 2021).
First results from the Sweeping Langmuir Probe (SLP) instrument on board PICASSO
Authors: Ranvier Sylvain , De Keyser Johan , Lebreton Jean-Pierre
Published: March 2021

The Sweeping Langmuir Probe (SLP) instrument on board the Pico-Satellite for Atmospheric and Space Science Observations (PICASSO) has been developed at the Royal Belgian Institute for Space Aeronomy.  PICASSO, an ESA in-orbit demonstrator launched in September 2020, is a triple unit CubeSat orbiting at about 540 km altitude with 97 degrees inclination. The SLP instrument includes four independent cylindrical probes that are used to measure the plasma density and electron temperature as well as the floating potential of the spacecraft. Along the orbit of PICASSO the plasma density is expected to fluctuate over a wide range, from about 1e8/m3 at high latitude up to more than 1e12/m3 at low/mid latitude. SLP can measure plasma density from 1e8/m3 to 1e13/m3. The electron temperature is expected to lie between approximately 1000 K and 10.000 K. Given the high inclination of the orbit, SLP will allow a global monitoring of the ionosphere. Using the traditional sweeping mode, the maximum spatial resolution is of the order of a few hundred meters for the plasma density, electron temperature and spacecraft potential. With the fixed-bias mode, the electron density can be measured with a spatial resolution of about 1.5 m. The main goals are to study the ionosphere-plasmasphere coupling, the subauroral ionosphere and corresponding magnetospheric features together with auroral structures and polar caps, by combining SLP data with other complementary data sources (space- or ground-based instruments). The first results from SLP will be presented.
Change of channel pattern and construction of fluvial terraces driven by SAMS since the LGM in southeastern South America: records from Tietê River, Brazil
Authors: Breda Caio , Nascimento Pupim Fabiano
Published: March 2021

The last 30 ka is a period marked by well-documented abrupt environmental changes on Earth. Despite the growing efforts to investigate the effects of past environmental changes in the fluvial dynamics, there is a lack of studies in intraplate tropical regions. Here, we applied geomorphological, sedimentological, and optically stimulated luminescence dating (OSL) technics to investigate the effects of environmental factors on the evolution of the Upper and Middle Tietê River during the Late Quaternary. Tietê River is one of the most important rivers of the southeast of Brazil, flowing from steepest to low-relief intraplate terrains, and under tropical climate. In order to understand the responses of the Tietê River system to environmental changes during the Late Quaternary, two main questions were tentatively answered: (i) what are the most important allogeneic factors for the evolution of this system?; (ii) how did climatic fluctuations affect river dynamics over time? We recognized a sequence of seven terraces, from 2 to 105 m above the channel, in the Middle Tietê valley. These terraces are formed by thin deposits (< 10 m), composed of sandy and conglomeratic sediments. The high and intermediate terrace levels of the Middle Tietê River are strath, while the low terraces of the middle reach are cut-and-fill. The formation of seven terrace levels in the Middle Tietê River was controlled by the combination of low erosion resistance of the lithological substrate and high stream power and coarse bedload that increase the erosion efficiency of the channels. OSL dating of sedimentary deposits in different terrace levels indicate 5 periods of aggradation in the Middle Tietê valley since the Last Glacial Maximum: 18.5 ± 2.0 ka; 9.8 ± 1.0 to 8.6 ± 0.8 ka; 7.1 ± 0.7 to 5.8 ± 0.5 ka; 4.2 ± 0.4 to 3.1 ± 0.3 ka; and 0.6 ± 0.06 ka. The results indicate that the activity of the South American Monsoon System induced the occurrence of climatic fluctuations and changes in vegetation cover in the river valleys of southeastern Brazil over the past 20 ka. The aggradation periods are correlated with more arid environmental conditions and sparser vegetation, while the incision events in the valley developed under transitions to humid environmental conditions and stimulated by vegetation recovery.

Key-words: Tietê River, fluvial evolution, fluvial terraces, Quaternary geochronology.
Implied ocean heat transport in CMIP6 models
Authors: Pearce Francesca , Bodas-Salcedo Alejandro , Thomas Christopher , Allen Thomas
Published: March 2021

The importance of heat transport in the ocean to maintain energy balance between different regions is well known, with heat typically being transported from the Equator to high latitudes. Ocean heat transport (OHT) can be separated into two different components; a divergent component which contributes directly to the Earths’ energy budget as it is the energy that converges in an ocean basin to balance the release of heat into the atmosphere, and a rotational component which does not affect the energy budget. Climate models show significant uncertainty in projections of ocean heat uptake, both in terms of the magnitude and geographical pattern. Since the oceans’ response under climate changes depends on the patterns of surface energy fluxes, it is important to assess the simulation of surface fluxes as a potential constraint of transient and long-term responses of the Earths’ climate. Assuming that the ocean absorbs all of the excess energy within the Earth system, it is possible to directly relate the net surface flux (NSF) over the ocean to divergent OHT, potentially providing a metric to quantify how well climate models are able to reproduce observed patterns of NSF and OHT. In this work, we present a detailed comparison of different methods used to calculate divergent OHT from the NSF over the ocean using data from various CMIP6 models. The methods investigated include a least-squares solution to a matrix equation in which energy convergence is related to NSF via the Earths’ energy imbalance, and solving a Poisson equation over the ocean surface (see Forget and Ferreira 2020). Comparison to observational estimates of OHT requires that the observational data set includes only sources of divergent heat transport, which is often not the case. Therefore, we intend to produce a data set of radiative energy fluxes that are consistent with both energy and water constraints (see Rodell et al. 2015, L’Ecuyer et al. 2015, Thomas et al. 2020) which can be subject to the same methods of determining OHT, and see how these estimates compare to the results from climate models.