bluuebunny/crossref_metadata_2025 huggingface dataset:
Charophyte biostratigraphy of continental deposits in a filled-karst system: A case study from the Eocene bauxite cover-sequence at Gánt (Vértes Hills, Hungary)
Authors: Trabelsi Khaled , Sames Benjamin , Wagreich Michael , Kázmér Miklós , Mindszenty Andrea , Martín-Closas Carles Martín-Closas
Published: March 2021

The Eocene ‘‘blue hole” freshwater limestones from the bauxite cover-sequence at the Gánt karst system (Vértes Hills), Transdanubian Central Range, north-western Hungary, have yielded rich charophyte assemblages of higher taxonomic and biostratigraphic interest. The taxonomic study of this flora allows revision and emendation of the species Raskyella peckii and facilitates the definition of a new evolutionary anagenetic lineage based on three successive anagenetic varieties of this species which were formerly considered as separate species or subspecies: Raskyella peckii var. peckii (early Lutetian–early Bartonian), Raskyella peckii var. caliciformis (early Bartonian), and Raskyella peckii var. vadaszii (late Bartonian). Based on these, we propose a new local charophyte biozonation with the new Raskyella peckii Superzone (Lutetian–Bartonian), subdivided into three successive charophyte partial range zones: The ‘Raskyella peckii peckii Zone’ (Lutetian–lowermost Bartonian) is locally characterized by an assemblage of R. peckii peckii, Gyrogona caelata forma caelata, G. caelata forma monolifera and Nitellopsis (Tectochara) palaeohungarica. The ‘Raskyella peckii caliciformis Zone’ (lower Bartonian) includes the local assemblage of R. peckii var. caliciformis, G. caelata forma caelata, G. caelata forma monolifera, G. caelata forma baccata, Nitellopsis (Tectochara) palaeohungarica and Chara media. The ‘Raskyella peckii vadaszii Zone’ (upper Bartonian) is composed of the local assemblage of R. peckii var. vadaszii, G. caelata forma bicincta, G. caelata forma baccata, G. caelata forma fasciata, G. tuberosa, Psilochara polita, Psilochara sp., Chara media and Chara subcylindrica. Future research may show the new local biozonation as applicable to whole Europe and complementing the current European charophyte biozonation. Our results show that the sequences from Gánt previously regarded as upper mid-Eocene (upper Lutetian–lower Bartonian) appear to comprise a longer chronostratigraphic interval, i.e. lower Lutetian till upper Bartonian, with also has implications on the understanding of the regional stratigraphy of the Transdanubian Central Range during the Eocene.
Coupling geochemical and isotopic tracers (δ18O, δ2H and 87Sr/86Sr) to quantify groundwater mixing in carbonate environment
Authors: Garin Thibaut , Ladouche Bernard , Arfib Bruno , Dewandel Benoit , Goncalves Julio
Published: March 2021

Carbonate aquifers are known as a major source for drinking water in the Mediterranean region. Therefore, qualitative and quantitative estimation of the groundwater resource are crucial, especially in area with densely populated areas.

In this study, geochemical and isotopic tracers (δ18O, δ2H and 87Sr/86Sr) have been used to discriminate different origins of groundwater and evaluate water-mass mixing in a Mediterranean carbonate environment. The case study, located in south-eastern France, offers an attractive geological context to explore strontium isotopic tracers: trias to cretaceous carbonate rocks, that have been eroded and locally resedimented in fluvial deposits during Oligocene extension and Quaternary periods. Moreover, many karst features act as sinking zones, generating fast infiltration. The 500 km² zone investigated has also a large range of elevation, from the sea to 1148m, giving an expected significant contrast in water isotopes. Monthly water samples have been collected in-situ for two years on ground and surface waters, in rivers, boreholes as well as karstic springs. Monthly rainwater samples provide the isotopic signal of the recharge at two distinct elevations and distance from the sea.

The hydrogeochemical signatures allow to discriminate the end-members of two main waterbodies as well as a slight marine influence on one borehole. Nitrates concentrations (NO3-) highlight anthropogenic influence on groundwater resources. A multi-tracer approach taking in account water-rock interaction, mixing processes and recharge, coupled with hydrogeological conditions and dye-tracing tests, leads to a conceptual model of this complex hydrosystem.
Galileo data integrity and consistency in the IGS consolidated navigation product
Authors: Andrei Octavian
Published: March 2021

The International GNSS Service (IGS) has been offering a broadcast navigation consolidated product (BRDC00IGS) since April 2017 (IGSMAIL-7455). This product is meant to support the expansion of the Global Navigation Satellite System (GNSS) ecosystem. The product dissaminates mixed navigation data parameters for all four global systems (GPS, GLONASS, Galileo, BeiDou), regional systems (QZSS, NavIC) and the augmentation systems (SBAS). The navigation data is derived from the original data over 24 hour period collected at the IGS global network. There is no public information how the product is generated. This study reports on the Galileo data consistency and integrity in the BRDC00IGS product. We use all available data by the end of 2020 (about 10M navigation messages). We carry out time series analysis on several derived parameters (such as repeat period) and look into the temporal signals affecting these parameters. We point out a number of benefits/limitations and propose several recommendations how the product may be further enhanced in the future to serve a larger spectrum of users.
Usage of computed tomography for investigation of the soil porosity in disturbed grassland 
Authors: Krebstein Kadri , Tõnutare Tõnu , Vennik Kersti , Virro Indrek , Tõnutare Tõnis , Kõlli Raimo , Soobik Liina
Published: March 2021

Soil disturbance will remarkably alter physical properties of the soil  and the recovery of the structure as well as mechanical strength recovery will take  years. Typically deforestation works, e.g. needed for the establishment of open military training areas, seriously influences soil mechanical state. Deforestation works involve processes like felling of trees, uprooting of stumps followed by levelling of ground. For the establishment of more favourable conditions for grass cover development, tree stumps and felling residues are mixed into the soil with a rotary thriller. Therefore, the final disturbed ground  has low density and high porosity resulting in low mechanical strength. On the  contrary, military training includes high intensity movement by soldiers and trafficking by vehicles. Thus, these types of activities presume stable soil conditions with a high mechanical strength. The aim of our research was to investigate soil density status of disturbed grassland with computed tomography. The soil samples were collected from the undisturbed area and from the grassland which was treated with the rotary thriller 2 years ago. The undisturbed soil samples were collected using plastic cylinders (of 10 cm diameter and 20 cm height) in 3 repetitions.  For comparison, smaller soil samples (5.3 cm diameter and 4 cm height) were obtained at 0, 5, 10, 15, 20, 30 cm depths  for determining the soil bulk density. In the  laboratory, the high resolution industrial computed tomography system Yxlon FF 35 CT was used with the larger soil samples. The soil samples were analyzed using the software Volume Graphics VGSTUDIO MAX 3.2.  Our results indicated the possibility of determination of distribution of pores in the soil and the changes in the porosity of soils depending on the soil treatment and the type.
Analyzing the paleoseismic history of the La Rouvière fault, unexpected source of the 11-11-2019, Mw4.9 Le Teil surface rupturing earthquake (Cévennes fault system, France) 
Authors: Ritz Jean-François , Baize Stéphane , Ferry Matthieu , Hannouz Estelle , Riesner Magali , Bollinger Laurent , Larroque Christophe , Audin Laurence , Manchuel Kevin , Rizza Magali , Jomard Hervé , Sue Christian , Arroucau Pierre , Billant Jérémy
Published: March 2021

The 11-11-2019 Le Teil earthquake (Mw4.9), located in the Rhône river valley occurred along the La Rouvière fault (LRF) within the NE termination of the Cévennes faults system (CFS). This very shallow moderate magnitude and reverse-faulting event inverted an Oligocene normal fault which was not assessed to be potentially active, causing surface rupture and strong ground shaking. Its morphology shows no evidence of cumulative reverse faulting during the Quaternary. All of this information raises the question of whether the fault was reactivated for the first time since the Oligocene during the Teil earthquake, or if it had broken the surface before, during the Quaternary period, but could not be detected. In addition, it poses the question of the potential reactivation of other faults of the CFS and other faults in metropolitan France as well.

To tackle those issues, we launched paleoseismic investigations along the LRF to analyze and characterize evidences of paleo-ruptures in Quaternary deposits. Twelve trenches were dug along the section that broke in 2019. The trenches were dug in aeolian deposits and slope colluvium lying against the ancient LRF normal fault mirror carved in the Barremian limestones. Five trenches yielded favorable Quaternary deposits to document deformation suggesting that one paleo-event, maybe more, occurred with kinematic characteristics (sense of movement, amount of displacement) similar to the 2019 event. The radiocarbon dating of the deformed units (“bulks” collected from the colluvium clayey-silty matrix) suggests, in particular, that at least one event occurred in the past 13 Ka (i.e. penultimate event prior to the Teil earthquake) . The fact that these events are not preserved in the morphology is explained by the small amount of displacement and a long return period, consistent with the low strain rate measured by GPS in this region (~10-9 yrs-1). Our study shows that it is therefore fundamental to carry out more detailed paleoseismological investigations in metropolitan France, especially along ancient faults favorably oriented with respect to the present stress field. Those are already planned in the next coming months along other segments of the CFS.
Spatial modelling of gully initiation in the Abaya-Chamo lakes catchments, southern Ethiopia
Authors: Belayneh Liuelsegad , Dewitte Olivier , Gulie Guchie , Poesen Jean , Kervyn Matthieu
Published: March 2021

Lake Abaya and Lake Chamo are located within the rift valley that cuts across eastern Ethiopia. Severe soil erosion, predominantly gully erosion in the midlands and highlands, and flash flooding along rivers in the lowlands resulted in sediment and nutrient accumulation in the rift lakes. In this study, conducted in four river catchments on the Western border of the Abaya-Chamo rift, an inventory of gully channels is made and factors controlling the location of gullies are analysed. The inventory, which was prepared using Google Earth imagery and field surveys, consists of 7336 gullies over a study area of 1050 km², resulting in a high average gully density (1.56 km.km-²) with specifically high densities (3.74 km.km-²)  in the Northern Shafé river catchment. Of all mapped gullies, 56% show signs of active erosion (i.e. mostly bare gully walls and bed, and/or fresh sediments deposited in the lower parts of the gully). In order to reduce the effects of gully erosion, it is vital to understand the factors controlling gully initiation and locations most susceptible to develop new gullies. Instead of using gully head, which due to head cut retreat might not be representative of the characteristics of the gully initiation point, a slope-area threshold (SA) is used to identify the most probable gully initiation point along existing gullies. The spatial susceptibility of these sites to gully initiation is then modelled using the frequency ratio and logistic regression methods using a set of 15 geo-environmental variables related to topography, soil texture, geology, rivers, knickpoints and land cover, as potential controlling factors. Active and inactive gullies are modelled separately. Slope, type of lithology, location of knickpoint rejuvenating the landscape through channel incision, distance from roads and mean annual rainfall are identified as very important controlling factors of gully initiation sites. The most susceptible gully erosion areas are observed in the steep midland, where limited population is living, and bare land and rangeland is dominant. The results show that the models are reliable and have a good prediction performance of gully initiation when using an independent validation dataset. The produced gully susceptibility maps highlight locations where soil and water conservation or other sustainable planning actions are required. Such maps are also needed to estimate the long-term contribution of gullies to the sediments delivered to the Abaya-Chamo Lakes.
3D-Microfabric reconstruction of Neoproterozoic diamictites from the Valjean Hills, California (USA)
Authors: Kettler Christoph , Pichler Katarina , Smirzka Daniel , Vandyk Thomas , Le Heron Daniel
Published: March 2021

Neoproterozoic rocks from the Kingston Peak Formation (KPF) in the Valjean Hills (USA) expose a succession of diamictites associated with major glacial events taking place during the Cryogenian, approximately 700 million years ago. Within any glacial period, diamictites are widespread and in addition, their mechanics of deposition are highly variable. Some are massive in appearance at outcrop or in hand specimen, and apparently lacking any information that allows their mode of emplacement to be elucidated. Yet the correct interpretation for deep time successions in this area is especially important, since it is debated whether the diamictites have a tectonically driven, gravitational (Mrofka & Kennedy, 2011) or direct (sub)glacial origin (Le Heron et al. 2016).

In this contribution we determine the origin of the diamictites based on its internal microfabric and associated microstructures. We base our method on the technique of Philips et al. (2011) for Quaternary sediments, by mapping the apparent longest axes of skeleton grains (ranging from fine-grained sand to fine-grained pebbles) in oriented thin sections and reconstructing their fabric in a 3D space, we could identify a bimodal signal in the orientation of the longest axes. Contrary to gravitational deposition, clasts in subglacial diamictites tend to align themselves to a stress field, induced by the movement of the glacier. Macroscopic observations (Fig. 1A), microtexture- and structures (Fig. 1B) as well as the reconstructed microfabric domains (Fig. 1C) suggests a subglacial origin. These circumstances suggest temperate glacial conditions with wet based ice sheets during the deposition of the KPF. Moreover, the quantitative data allow confident flow directions to be extracted from seemingly chaotic diamictites.

 

Figure 1: (A) Valjean Hills Diamictite (label is 5x5 cm), (B) Rotational structure around bigger skeleton grain, (C) traced long axes of clasts (white lines) and interpreted  microfabric domains (blue, orange)

 

References:

Le Heron, D.P., Tofaif, S., Vandyk, T. & Ali, D.O. (2017): https://doi.org/10.1130/G38460.1

Mrofka, D., Kennedy, M., (2011):  https://doi.org/10.1144/M36.40

Phillips, E. et al., (2011): https://doi.org/10.1016/j.quascirev.2011.04.024
Statistical study of sedimentary phosphorus content in French reservoirs and identification of P variability driving factors 
Authors: Lix Claire , Rabiet Marion , Grybos Malgorzata , Danis Pierre-Alain , Blondeau Anne , Louvet François , Deluchat Véronique
Published: March 2021

Phosphorus (P), an essential element for living organisms, is often considered as the limiting factor of eutrophication in aquatic environments, especially in reservoirs. In order to limit their environmental degradation and to meet the requirements of good ecological quality imposed by the European Water Framework Directive (WFD), actions have been implemented in the past decades to reduce the exogenous P influx to reservoirs. However, despite the decrease in external P inputs to the water from agriculture and domestic wastewater, eutrophication keeps expanding due to sedimentary P flux to the water column. Assessing the quality of sediments in reservoirs and the risk of of sedimentary P transfer to the water column is therefore a major issue. The POMOSED project aims to investigate the relevance of the WFD regulatory parameters, monitored since 2005, in the evaluation of sediment quality with respect to P. This work presents an inventory of sedimentary P contents in French reservoirs and identifies the factors contributing to the observed P variability from the physico-chemical sedimentary composition and the reservoirs and watersheds characteristics.

Statistical analyses were conducted on sedimentary composition data (total phosphorus (TP), iron (Fe), manganese (Mn), aluminium (Al), Kjeldahl nitrogen (NTK) and organic carbon (OC)) from 219 French reservoirs. The characteristics of their watersheds (geology, altitude, agricultural and artificial surfaces, …) and their morphology (e.g. depth,  surface area, …) were also included in the statistical analyses.

The sediments showed large variability in the TP concentration varying from 172 to 4350 mg.kg-1 with mean and median values of 1310 and 1060 mg.kg-1 respectively. The variability of sedimentary TP was observed both spatially and temporally. We highlighted significant correlations of PT content with Fe, Al, NTK and OC. We pointed out that the geological substratum, the level of anthropization of the watershed and the depth of the reservoirs are driving factors for TP concentration in sediments. Therefore, the WFD monitoring allows to distinguish several typologies of sediment with respect to TP. The typologies inducing an enrichment in TP of the sediments are crystalline substrate sediments rich in Fe and OC, deep reservoirs inducing anoxia development and an anthropized watershed. However, an enrichment in TP of the sediments does not necessarily indicate an anthropic pressure as shown by the influence of geology and the composition of sediments. These results might be included into multiple linear models linking PT concentrations to the other elements concentrations (CO and Fe) and the different factors (geology > anthropization > reservoir depth).
Combining citizen science and artificial intelligence to facilitate geology outreach and capture geodiversity: prospects from the RockNet project
Authors: Bouziat Antoine , Desroziers Sylvain , Feraille Mathieu , Lecomte Jean-Claude , Cornet Christophe , Cokelaer François , Divies Renaud
Published: March 2021

Popularizing and disseminating a basic level of geological knowledge and understanding to the general public has become an important issue, either to valorize and protect our natural heritage, or to facilitate public engagement in environmental and energy debates. Emergent technologies and the increasing digitalization of our societies broaden the range of tools available to address this topic. In this talk, we focus on the prospects enabled by the combination of citizen science and Artificial Intelligence (AI), building on the birth of the RockNetTM project. Inspired by the sucess of the Pl@ntNet project for botanical science outreach, RockNetTM aims at developping a mobile application, whose users can photograph rock samples and get a lithological classification from an AI algorithm. By doing so, a participative data base of rock images is progressively gathered and shared among all users. Meanwhile the most expert ones can correct the automated facies identification to gradually improve the AI capabilities. Then the resulting tool collectively produced becomes a possible support for geoscience outreach, relying on the citizens' curiosity for their immediate geological environment. A first prototype, handling 12 different lithological classes, has already been developed and trained on several thousand pictures. From this practical experience, we illustrate the potential of this kind of technology and the numerous challenges to consider before a large-scale diffusion of the application.   
New applications for an EMIC coupled to an atmospheric chemistry model - The University of Victoria Earth system climate model version 2.10 + FAIR chemistry module
Authors: MacIsaac Alexander J. , Mengis Nadine , Zickfeld Kirsten , Nzotungicimpaye Claude-Michel
Published: March 2021

As an Earth system model of intermediate complexity (EMIC), the University of Victoria Earth system climate model (UVic-ESCM) has a comparably low computational cost (4.5–11.5 h per 100 years on a simple desktop computer). It is therefore a well-suited tool to perform experiments that are not yet computationally feasible in a state-of-the-art Earth system model. For example, the UVic-ESCM can be used to perform large perturbed parameter ensembles to constrain uncertainties, but also run a multitude of scenarios while at the same time simulating a well resolved carbon cycle. Thanks to its representation of many important components of the carbon cycle and the physical climate and its ability to simulate dynamic interactions between them, the UVic-ESCM is additionally a more comprehensive tool for process level uncertainty assessment compared to integrated assessment models (IAMs).

The coupling of this EMIC with an atmospheric chemistry module based on the FAIR simple climate model, now allows to directly implement GHG emission files as an input to the model, which makes it a valuable tool for many ‘what-if’ questions about climate turnaround times. Especially in the context of assessing the carbon cycle responses to future long-term climate change scenarios including e.g. marine CDR or terrestrial CDR implementations. In this presentation we will introduce this new model setup and show examples of first applications of this novel tool, while showcasing the advantages that it brings about. 
Isotopic anomalies in water vapor during an atmospheric river event at Dome C, East Antarctic plateau, controlled by large-scale advection and boundary layer processes
Authors: Agosta Cécile , Davrinche Cécile , Leroy-Dos Santos Christophe , Berchet Antoine , Landais Amaëlle , Fourré Elise , Orsi Anaïs , Prié Frédéric , Amory Charles , Favier Vincent , Fettweis Xavier , Genthon Christophe , Kittel Christoph , Veron Dana , Wille Jonathan
Published: March 2021

On December 19-21, 2018, an atmospheric river hit the French-Italian Concordia station, located at Dome C, East Antarctic Plateau, 3 269 m above sea level. It induced an extreme surface warming (+ 15°C in 3 days), combined with high specific humidity (multiplied by 3 in 3 days) and a strong isotopic anomaly in water vapor (+ 15 ‰ for δ18O). The isotopic composition of water vapor monitored during the event may be explained by (1) the isotopic signature of long-range water transport, and by (2) local moisture uptake during the event. In this study we quantify the influence of each of these processes.

To estimate the isotopic composition of water vapor advected by long-range transport, we perform back-trajectories with the FLEXible PARTicle dispersion model FLEXPART. We retrieve meteorological conditions along different trajectories between the moisture uptake area and Concordia, and use them to compute isotopic fractionation during transport with the mixed cloud isotope model MCIM. While intermediate conditions along the trajectory do not seem to have a major impact on the final isotopic composition (less than 0.1 ‰), the latter appears sensitive to surface conditions (temperature, pressure and relative humidity) in the moisture uptake area (±5.1 ‰). As the event is characterized by the presence of liquid water clouds above Concordia, we show additional sensitivity tests exploring the impact of mixed phase clouds on the water vapor isotopic composition.

Finally, we perform a water vapor mass budget in the boundary layer using observations and simulations from the regional atmospheric model MAR, ran with and without drifting snow. The presence of mixed-phase clouds during the event induced a significant increase in downward longwave radiative fluxes, which led to high turbulent mixing in the boundary layer and to heavy drifting snow (white-out conditions). Using MAR simulations, we show that a significant part of the atmospheric water vapor originates from sublimation of drifting snow particles removed from the snowpack. Consequently, the isotopic signal monitored in water vapor during this atmospheric river event reflects both long-range moisture advection and interactions between the boundary layer and the snowpack. Only specific meteorological conditions driven by the atmospheric river, and their associated intense poleward moisture transport, can explain these strong interactions.
Chorus and hiss scales in the inner magnetosphere: statistics from high-resolution filter bank (FBK) Van Allen Proves multi-point measurements
Authors: Agapitov Oleksiy , Mourenas Didier , Artemyev Anton , Breneman Aaron , Bonnell John , Hospodarsky George , Wygant John
Published: March 2021

The spatial scales of whistler-mode waves, determined by their generation process, propagation, and damping, are important for assessing the scaling and efficiency of wave-particle interactions affecting the dynamics of the radiation belts. We use multi-point wave measurements in 2013-2019 by two identically equipped Van Allen Probes spacecraft covering all MLTs at L=2-6 near the geomagnetic equator to investigate the spatial extent of active regions of chorus and hiss waves, their wave amplitude distribution in the source/generation region, and the scales of chorus wave packets, employing a time-domain correlation technique to the spacecraft approaches closer than 1000 km, which happened every 70 days in 2012-2018 and every 35 days in 2018-2019. The correlation of chorus wave power dynamics using two spacecraft measurements is found to remain significant up to inter-spacecraft separations of 400 km to 750 km transverse to the background magnetic field direction, consistent with previous estimates of the chorus wave packet extent, but indicating the likely presence of two different scales of about 400 km and 750 km. Our results further suggest that the chorus source region can be slightly asymmetrical, more elongated in either the azimuthal or radial direction, which could also explain the aforementioned two different scales. An analysis of average chorus and hiss wave amplitudes at separate locations similarly reveals different radial and azimuthal extents of the corresponding wave active regions, complementing previous results based on THEMIS spacecraft statistics mainly at larger L>6. Both the chorus source region scale and the chorus active region size appear smaller inside the outer radiation belt (at L< 6) than at higher L-shells.
Legacy effects of climate overshoot scenarios in permafrost-affected regions
Authors: de Vrese Philipp , Brovkin Victor
Published: March 2021

Difficulties to quickly reduce carbon emissions to levels compatible with the long-term goal of the Paris Agreement increase the likelihood of scenarios that temporarily overshoot the respective climate targets. We used simulations with JSBACH, the land surface component of the Max-Planck-Institute for Meteorology’s Earth system model MPI-ESM1.2 to investigate the long-term response of the terrestrial Arctic to climate stabilization at such a climate target. In particular, we seek to answer the question whether the state of permafrost-affected soils and the Arctic carbon cycle could converge to different equilibria depending on the climate trajectory that precedes climate stabilization at 1.5°C above pre-industrial levels. To this end, we compare simulations that are forced with the same non-transient atmospheric conditions – corresponding to the 1.5°C-target --, but started from different initial conditions. One simulation was initialized with the conditions before and one simulation with the conditions after a temperature overshoot which follows SSP5-8.5 until the year 2100 subsequent to which the atmospheric conditions are reversed to the 1.5°C-target. Our results reveal that feedbacks between water-, energy- and carbon cycles allow for path-dependent steady-states in permafrost-affected regions. These depend on the soil organic matter content at the point of climate stabilization, which is significantly affected by the soil carbon loss resulting from overshooting the climate target. Here, the simulated steady-states do not only differ with respect to the amount of carbon stored in the frozen fraction of the soil, but also with respect to soil temperatures, the soil water content and even net primary productivity and soil respiration.
Mechanisms of multiple, anomalous melt events at Summit Station, Greenland in summer 2019
Authors: Walden Von , Guy Heather , Cox Christopher , Neff William , Neely Ryan , Shupe Matthew
Published: March 2021

Above freezing temperatures and melting surface snow have occurred at Summit Station (3250 m asl), atop the Greenland Ice Sheet, only five times in the last 800 years, including once in 2012 and twice 2019 (June 12; July 29-31). Such events are linked to southerly advection of continental air that cross the North Atlantic as atmospheric rivers (ARs). The specific mechanisms that are responsible for these rare events appear to be varied and complex. While the 2012 event was supported by anomalous cloud forcing caused by thin, liquid-bearing clouds, the two events in 2019 occurred under both clear and cloudy conditions. The net surface radiation measured during the 2019 events was actually similar between clear (~47 W m-2) and cloudy (~52 W m-2) conditions, and, surprisingly, these values are unremarkable for afternoon conditions in summer at Summit Station.

Observations from the ICECAPS-ACE project at Summit Station (including radiative and turbulent fluxes, surface skin temperature, snow pit stratigraphy) allow a process-level analysis of the mechanisms that transfer energy from the AR events into local melting. By combining the measurements with a finite-volume diffusion model of the sub-surface temperature field, we find that a concentration of energy in the surface layer caused by converging fluxes toward the surface from both directions (upward from within the snowpack and downward from the atmosphere) led to initiation of both of the 2019 melt events. Thus, coupling between the atmosphere and the snowpack, and the timing of atmospheric fluctuations, appear important, and are suggestive that preconditioning of the snowpack from events prior to the day of melt may be a factor. Both sensible and latent heat fluxes were relatively small during these melt events while several regimes of commonly occurring radiative processes were observed. Under cloudy conditions, longwave cloud radiative forcing played a role, while under clear skies, lower surface albedo was sufficient to make up the difference of the absence of cloud forcing. For example, during the July 2019 event, the surface snow albedo decreased significantly from 0.86 to 0.80, which facilitated greater absorption of solar radiation. These findings are supportive of the notion that longwave processes are triggers of melt while shortwave processes persist melt. he co-dependent roles of the radiative and subsurface heat fluxes during the 2019 events suggest that the rarity of melt at Summit Station may be explained by preconditioning processes, and that a particular sequence of events over several days leading up to melt may be important.
Optimising a regional Antarctic Ice Sheet model to investigate basal conditions and initialise transient experiments
Authors: Gladstone Rupert , Zhang Yufang , Zwinger Thomas , Gillet-Chaulet Fabien , Wolovick Michael , Moore John , Zhao Chen , Wang Yu , Werder Mauro
Published: March 2021

Computer models for ice sheet dynamics are the primary tools for making future predictions of ice sheet behaviour, marine ice sheet instability, and ice sheet contributions to sea level change.  Such modelling studies face a number of challenges, and we consider here two examples.  The dominant mode of flow for ice streams is sliding at the bed, and the physical processes that control sliding are hard to observe. Ice sheet models often prescribe basal resistance as a function of sliding velocity.  But laboratory experiments and real-world observations indicate that basal resistance is also dependent on the water pressure in the sub-glacial hydrologic system, a property that is hard to constrain.  Initialising an ice sheet model for future projections is usually implemented either by a multi-millennial spin up or else by optimisation simulations, both of which have significant drawbacks.  In particular, long spin-up simulations cannot easily ensure a close match to present-day ice geometry, and optimisations cannot easily ensure an overall ice sheet mass balance that matches the present-day mass balance.

Using a 3D Stokes-flow ice dynamic model, we carry out optimisations for two Antarctic catchments: The Pine Island Glacier (PIG) in West Antarctica and the Lambert-Amery Glacier System (LAGS) in East Antarctica.  We optimise both the basal resistance and flow enhancement in order to minimise discrepancy between modelled and observed (from satellite) horizontal velocities at the ice upper surface.  We use these optimised model configurations to estimate the transient mass trend and also look at the 3D velocity field, its sensitivity to choice of boundary conditions in the normal direction at upper and lower surfaces, and its implications for the 3D temperature structure.  These simulations provide an estimate of the present-day thermo-mechanical state of the PIG and LAGS.

We demonstrate that constraining only horizontal velocity in the optimisations can lead to unrealistic normal velocities at the upper surface.  We show that this can, in turn, strongly impact on the catchment’s total mass budget (through locally unconstrained thinning/thickening rates) and lead to a large-scale bias in temperatures simulated using the optimised model with the steady state assumption, due to unphysical advection of heat through the ice upper surface.

We employ the optimised model to estimate basal melt, due mainly to friction heat, and drive a subglacial hydrology model beneath the PIG, providing a model-based estimate of the distribution of basal water pressure.  We use this, along with simulated sliding velocity and basal resistance, to evaluate some commonly used sliding relations.
Fire-induced catchment erosion on a depleted soil system from GeoWEPP and RUSLE models, Santa Olga, Chile
Authors: Tolorza Violeta , Poblete Dagoberto , González Virginia I. , Zambrano-Bigiarini Mauricio , Cabezas Julián , Galleguillos Mauricio
Published: March 2021

The recent increase in frequency and extent of severe wildfires in South-Central Chile is degrading the already eroded soils of the Coastal Cordillera. Spatially explicit quantification of erosion triggered by that disturbances may reveal useful information for soil conservation and land planning purposes, which is especially relevant in drinking-water catchments. We compared estimations of water erosion using a process-based and an empirical modeling approaches in a small (173 ha) burned drinking water catchment. To this end, we implemented the GeoWEPP process-based model and the RUSLE empirical approach for different scenarios of wildfire severity using remote sensing, in situ soil and hydro-meteorological data (2001-2019). Individual Hydrologic Response Units resulted in very low erosion rates in GeoWEPP respect to RUSLE, while both simulations represent low erosion rates respect to observations reported for other latitudes of the Coastal Cordillera. Those low erosion rates could be explained by low rainfall erosivity and high critical shear stress, which in turn is a consequence of soil compaction.  The spatial variations of the modeled sediment yields (2001-2019) were associated both to the wildfire and to the land management at hillslopes, which involves clear cut timber harvest at most forest plantations areas. A better quantification of those erosion processes is necessary to improve the understanding of the evolution of Chilean forestry landscape, in order to prioritize efforts for soil conservation and ecosystem restoration.
Origin and significance of the antimony mineralisation associated to mafic intrusions in the Iberian Zone and the Central Armorican Domain
Authors: Gloaguen Eric , Campos Héctor , Pochon Anthony , León Higueras Pablo , Lorenzo Saturnino , Esbrí José-María , Iacono-Marziano Giada , Lima Alexandre
Published: March 2021

In the Central Iberian Zone (CIZ) and its French counterpart, the Central Armorican Domain (CAD), widespread swarms of mafic dykes with various ages and compositions are known. Indeed, numerous mafic events are recognized in the late Neoproterozoic, in the Cambrian to the Ordovician, in the Ordovician to the Devonian, at the Devonian-Carboniferous boundary, in the Permian and in the Jurassic. Such a succession of mantle partial melting events, localised or generalized, may have strong consequences (i) on the composition and the homogeneity of the mantle below both the CIZ and CAD, and (ii) on the transfert of metals in the overlying crust. Moreover, the mantle below these domains must have been modified also by the subduction of large to small oceanic crusts from the Iapetus, the Rheic, the Galicia-Moldanubian and the Paleo-tethys. Although the occurrences of paleo-subductions below the CIZ and CAD remain discussed, the southern border of the CIZ, the Ossa-Morena Zone (OMZ), is considered as a suture zone resulting from a subduction followed by a collision between 390 and 360 Ma (D1), according to the 2 opposite structural vergences at the CIZ/OMZ boundary, as well as the location of a NE-dipping slab imaged by seismic profiles. In the Armorican massif, the end of subduction is also dated at 360 Ma and associated to a north-directed subduction. The trace of this subduction below the CAD is visible in the tomographic dataset. Interestingly, these two domains (CIZ and CAD) contain the largest number of Palaeozoic antimony deposits, antimony being a volatile element. In these domains, the large clustering of antimony deposits and occurrences is observed within a ca 100km wide bands along their southern parts. In the two domains, the antimony deposits are frequently spatially associated with diabase dykes. Diabase dykes and associated antimony mineralisation have been dated at 360 Ma in the CAD but remain temporally unconstrained in the CIZ. Nevertheless, since these dykes are strongly affected by the Variscan deformation a minimum age of 350 Ma is inferred. Both, the peculiar composition of these diabase dykes, relatively enriched in Cs, Li, Pb and relatively depleted in K and Rb, the spatial association with antimony at the end of a 360Ma subduction, suggest a link between antimony and a ca 360Ma mafic magmatism which could result from the partial melting of a subduction-related metasomatized mantle.

This work was funded by the ANR (ANR-19-MIN2-0002), the AEI (MICIU/AEI/REF.: PCI2019-103779), the FCT (ERA-MIN/0005/2018) and author’s institutions in the framework of the ERA-MIN2 AUREOLE project (https://aureole.brgm.fr).
Machine Learning analysis of seismic signals recorded at Stromboli Volcano
Authors: Fenner Darius , Rümpker Georg , Stöcker Horst , Chakraborty Megha , Li Wei , Faber Johannes , Zhou Kai , Steinheimer Jan , Srivastava Nishtha
Published: March 2021

At Stromboli, minor volcanic eruptions occur at time intervals of approximately five minutes on average, making it one of the most active volcanoes worldwide. In addition to these mostly harmless events, there are also stronger eruptions and paroxysms which pose a serious threat to residents and tourists. In light of recent developments in Machine Learning, this study attempts to apply these new tools for the analysis of the time-varying volcanic eruptions at Stromboli. As input for the Machine-Learning approach, we use continuous recordings of seismic signals from two seismometers on the island. The data is available from IRIS  and includes records starting in 2012 up to the present. 

One primary challenge is to label and classify the data, i.e., to discriminate events of interest from noise. The variety of signal-appearance in the recorded data is wide, in some periods the events are clearly distinguishable from noise whereas, in other cases relevant events are obscured by the high noise level. To enable the event-detection in all cases, we developed the following algorithm: in the first step, the seismic data is pre-processed with an STA/LTA-Filter, which allows detection of events based on a prominence threshold. However, due to the diversity of signal patterns, a fixed set of hyperparameters (STA- and LTA-window length, prominence threshold, correlation coefficient) fails to reliably extract the relevant events in a consistent manner. Therefore, the (time-varying) noise level of the recordings is used as an additional key indicator. After this, the hyperparameters are optimized. The automatic adaptation is then used for labeling the continuous seismic data.

After extracting the events based on this approach, a machine learning model is trained to analyze the recordings for possible patterns in the interval times and the event amplitudes. This study is expected to provide constraints on the possibility to detect complex time-dependent patterns of the eruption history at Stromboli.
Amplitude of paleosecular variations during the Cretaceous superchron: Okhotsk-Chukotka Volcanic Belt, high latitudes
Authors: Bobrovnikova Elizaveta , Lebedev Ivan
Published: March 2021

Studying of paleosecular variations (PSV) over geological time allows us to characterize not only the behavior and evolution of the geomagnetic field, but also to estimate the rate of formation of large igneous provinces (LIP). In order to use this paleomagnetic tool, the amplitude of paleosecular variations during the corresponding time interval has to be known, but for the end of the Cretaceous superchron, in particular for high latitudes, such the data sets are extremely small. Our study is aimed at obtaining a limit on the PSV amplitude for Late Cretaceous in order to use these data to estimate the rate of formation of the Okhotsk-Chukotka Volcanic Belt.

The formation of a paleomagnetic record in volcanic flows occurs by acquiring a thermal remanent magnetization (TRM) during their cooling below the Curie temperature of the magnetic minerals. Direction of this TRM can be used for calculation of the virtual geomagnetic pole (VGP), which characterizes the direction of the geomagnetic field at a given time and place. The angular dispersion of virtual geomagnetic poles (VGP scatter, Sb) is generally accepted as a measure of the paleosecular variations and uses to assess the duration of volcanic section formation. If the volcanic section was formed for a long time (more than 10 000 years), then the amplitude of the recorded geomagnetic variations will correspond to the expected dispersion for a given latitude. In the case of significantly higher eruption rates, the amplitude of the recorded PSV will be lower than it is predicted by the model for a given latitude.

During the 2019-2020 field seasons paleomagnetic studies were carried out on a number of Late Cretaceous volcanic sections of the Okhotsk-Chukotka Volcanic Belt located in the Bilibinsky District of the Chukotka Region. VGPs and their scatter were calculated for 79 flows of the Kupol object. Preliminary results show that the amplitude of PVS in the Cretaceous for high latitudes of the northern hemisphere was close to that for the last 5 million years (Sb=21.4, [19.0; 23.9]).

The work is supported by the Russian Science Foundation grant N 19-47-04110.
Data Stewardship Practices for Earth Observation Transient and Optimized Analysis Platforms
Authors: Bugbee Kaylin , Ramachandran Rahul , Peng Ge , Kaulfus Aaron
Published: March 2021

Access to valuable scientific research data is becoming increasingly more open, attracting a growing user community of scientists, decision makers and innovators. While these data are more openly available, accessibility continues to remain an issue due to the large volumes of complex, heterogeneous data that are available for analysis. This emerging accessibility issue is driving the development of specialized software stacks to instantiate new analysis platforms that enable users to quickly and efficiently work with large volumes of data. These platforms, typically found on the cloud or in a high performance computing environment, are optimized for large-scale data analysis. These platforms can be transient in nature, with a defined life span and a focus on improved capabilities as opposed to serving as an archive of record. 

 

While these transient, optimized platforms are not held to the same stewardship standards as a traditional archive, data must still be managed in a standardized and uniform manner throughout the platform. Valuable scientific research is conducted in these platforms, making these platforms subject to open science principles such as reproducibility and accessibility. In this presentation, we examine the differences between various data stewardship models and describe where transient optimized platforms fit within those models. We then describe in more detail a data and information governance framework for Earth Observation transient optimized analysis platforms. We will end our presentation by sharing our experiences of developing such a framework for the Multi-Mission Algorithm and Analysis Platform (MAAP).
Impact of fracture sealing on their hydraulic and mechanical properties
Authors: Deng Qinglin , Schmittbuhl Jean , Bloech Guido , Cacace Mauro
Published: March 2021

In deep tight reservoirs like Enhanced Geothermal Systems (EGS), the fracture flow often plays a dominant role. The hydraulic and mechanical behaviors of the fracture are affected by a couple of factors such as the sealing deposits owing to mineral cementation. Here we aimed to investigate the impact of the sealing material on the hydro-mechanical properties of a rough fracture using a well-established self-affine rough fracture model. We developed finite element model based on the MOOSE/GOLEM framework dedicated to modeling coupled Hydraulic-Mechanical (HM) process of the rock-fracture system. We conducted numerical flow through a granite reservoir hosting one single large and partly sealed fracture of size 512x512 m2. Navier-Stokes flow and Darcy flow are solved in the 3-dimensional rough aperture and in the embedding poro-elastic matrix, respectively. In order to mimic the impact of the fracture sealing material on the physical properties of the rock-fracture system, we sequentially increased the amount of the fracture-filling material in the rough fracture by changing the thickness of the sealing deposits.  The evolution of the contact area, fracture permeability, fracture diffusivity and normal fracture stiffness, is monitored up to the percolation threshold of the fluid flow. We show that sealing induces strong permeability anisotropy, significant decrease of hydraulic diffusivity and increase of fracture stiffness. The results have strong implications for optimizing the stimulation strategy like chemical stimulation of fractured reservoirs, as well as understanding the fluid-induced seismicity.