bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Permian basalts in the northwestern Sichuan Basin, SW China: Implications for the geodynamics and thermal effect of the Emeishan mantle plume
Authors: Liu Xiaoyu , Qiu Nansheng
Published: March 2020

The Middle-Late Permian Emeishan large igneous province (ELIP), located in the western margin of Yangtze craton, SW China, is regarded as the result of the impingement of a mantle plume onto the lithosphere. However, little is known about the petrogenesis of Late Permian basalts in Sichuan Basin, which were previously considered to be located outside the ELIP. Here we report new petrographic, major elements, trace elements and isotopic data (Sr-Nd-Pb) for Late Permian basalts in the boreholes from the northwestern Sichuan Basin. These basaltic rocks are characterized by low SiO2 contents (47.17-49.40 wt.%), high TiO2 contents (3.38-4.11 wt.%) and Ti/Y ratio (539-639), moderate total alkalis contents (Na2O+K2O, 3.36-6.01 wt.%) and Mg# values (40.93-46.04), which geochemically resemble the Emeishan high-Ti basalts. These rocks are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREE), and have (La/Yb)N ranging from 9.95 to 11.78, showing that typical oceanic island basalt (OIB)-like normalized patterns. The fractionation of MREE to HREE suggests that the basalts were generated by low degree of partial melting within the garnet stability field. Low initial 87Sr/86Sr ratios (0.70572-0.70676; t=260 Ma), Pb isotopic ratios [206Pb/204Pb(t) (18.062-18.637), 207Pb/204Pb(t) (15.574-15.641), 208Pb/204Pb(t) (38.33-38.98)], and slightly high εNd(t) values (-0.03 to +1.34) indicate that the magma formed from a deep mantle source that may possibly be a mantle plume and have negligibly been affected by crustal contamination. This inference is further supported by high Nb/U ratios (20.56-25.70), low Th/Nb (0.17-0.19) and Th/Ta ratios (2.77-3.14), and no visible Nb and Ta anomalie. In addition, thermal history reconstruction using paleogeothermal indicators in the study area shows that the Lower Paleozoic to Middle Permian formations experienced an intensive thermal event and abnormal high heat flow value reached 118.0 mW/m2 at the Late Permian, which may be due to the mantle plume magma upwelling. The geochemical and geothermal characteristics all demonstrate that these basalts were probably generated in response to the Emeishan mantle plume. Thus, we conclude that the ELIP may have larger areal extent and has been played an important role on the thermal evolution of source rocks in the Sichuan basin.
Rift linkage processes in areas of incipient oceanic spreading: examples from Afar
Authors: Pagli Carolina , La Rosa Alessandro , Illsley-Kemp Finnigan
Published: March 2020

Mid-ocean ridges are segmented and offset along their length. However, the kinematics of rift linkage and the initiation of oceanic transform faults in magmatic rifts remain debated. Crustal deformation patterns from the Afar continental rift provide evidences of how rifts grow to link in an area of incipient seafloor spreading. Here we present examples of rift linkage processes in Afar integrating seismicity and geodetic (InSAR and GPS) measurements, and explained by numerical and analytical models. We show that in central Afar overlapping spreading rifts link through zones of rift-perpendicular strike-slip faulting at the tips of the spreading rifts, demonstrating that distributed extension drives rift-perpendicular shearing. Conversely, in northern Afar we identify a linkage zone between the Erta Ale and Tat Ali segments where shear is accommodated by a conjugate set of oblique slip faults. There, InSAR modelling of a ML 5.1 earthquake in 2007 show that overall right-lateral shear is accommodated primarily by oblique left-lateral slip along faults subparallel to the rift segments but an active conjugate fault system with right-lateral slip is also highlighted by low-to-moderate seismicity during 2011-2013. Thermomechanical models of transform fault formation are consistent with the presence of a proto-transform fault that may develop into a throughgoing transform in the future. Our results provide evidences that offset rift segments during continental breakup can be linked by a wide variety of strain types and proto-transform zones can form before the onset of seafloor spreading.
German Bight Storminess over the Last Century
Authors: Krieger Daniel , Krueger Oliver , Feser Frauke , Weisse Ralf , Tinz Birger , von Storch Hans
Published: March 2020

Assessing past storm activity provides valuable knowledge for economic and ecological sectors, such as the renewable energy sector, insurances, or health and safety. However, long time series of wind speed measurements are often not available as they are usually hampered by inhomogeneities due to changes in the surroundings of a measurement site, station relocations, and changes in the instrumentation. On the contrary, air pressure measurements provide mostly homogeneous time series as the air pressure is usually unaffected by such factors.

Therefore, we perform statistical analyses on historical pressure data measured at several locations within the German Bight (southeastern North Sea) between 1897 and 2018. We calculate geostrophic wind speeds from triplets of mean sea level pressure observations that form triangles over the German Bight. We then investigate the evolution of German Bight storminess from 1897 to 2018 through analyzing upper quantiles of geostrophic wind speeds, which act as a proxy for past storm activity. The derivation of storm activity is achieved by enhancing the established triangle proxy method via combining and merging storminess time series from numerous partially overlapping triangles in an ensemble-like manner. The utilized approach allows for the construction of robust, long-term and subdaily German Bight storminess time series. Further, the method provides insights into the underlying uncertainty of the time series.

The results show that storm activity over the German Bight is subject to multidecadal variability. The latest decades are characterized by an increase in activity from the 1960s to the 1990s, followed by a decline lasting into the 2000s and below-average activity up until present. The results are backed through a comparison with reanalysis products from four datasets, which provide high-resolution wind and pressure data starting in 1979 and offshore wind speed measurements taken from the FINO-WIND project. This study also finds that German Bight storminess positively correlates with storminess in the North-East Atlantic in general. In certain years, however, notably different levels of storm activity in the two regions can be found, which likely result from shifted large-scale circulation patterns.
Neural Network Applications in Earthquake Prediction (1994-2019): Meta-Analytic & Statistical Insights on their Limitations
Authors: Mignan Arnaud , Broccardo Marco
Published: March 2020

In the last few years, deep learning has solved seemingly intractable problems, boosting the hope to find approximate solutions to problems that now are considered unsolvable. Earthquake prediction, the Grail of Seismology, is, in this context of continuous exciting discoveries, an obvious choice for deep learning exploration. We reviewed the literature of artificial neural network (ANN) applications for earthquake prediction (77 articles, 1994-2019 period) and found two emerging trends: an increasing interest in this domain over time, and a complexification of ANN models towards deep learning. Despite the relatively positive results claimed in those studies, we verified that far simpler (and traditional) models seem to offer similar predictive powers, if not better ones. Those include an exponential law for magnitude prediction, and a power law (approximated by a logistic regression or one artificial neuron) for aftershock prediction in space. Due to the structured, tabulated nature of earthquake catalogues, and the limited number of features so far considered, simpler and more transparent machine learning models than ANNs seem preferable at the present stage of research. Those baseline models follow first physical principles and are consistent with the known empirical laws of Statistical Seismology (e.g. the Gutenberg-Richter law), which are already known to have minimal abilities to predict large earthquakes.
The summers of 1531–1540 in Central Europe: The driest decade of the past five centuries?
Authors: Brázdil Rudolf , Dobrovolný Petr , Kiss Andrea , Oliński Piotr , Řezníčková Ladislava
Published: March 2020

The summers of 1531–1540 in the Czech Lands were, according to three drought indices (SPI, SPEI, Z-index) reconstructed from the Czech documentary evidence and instrumental records (Brázdil et al., Clim. Res., 2016), the driest decade during the past five centuries. Based on documentary data, dry patterns of different intensity (represented e.g. by dry spells, low number of precipitation days, drying rivers and lack of water sources, frequent fires) for central Europe (Germany, Switzerland, Austria, Czech Republic, Poland, Slovakia and Hungary) were well expressed for summers in 1532, 1534–1536, 1538 and particularly in 1540. Summer droughts derived from documentary data in central Europe were confronted with gridded summer precipitation totals reconstructed from instrumental, documentary and selected natural proxies (Pauling et al., Clim. Dyn., 2006) and further with summer scPDSI reconstructed from tree-ring widths in the Old World Drought Atlas – OWDA (Cook et al., Sci. Adv., 2015). While in precipitation reconstruction summers of 1531–1540 represented the driest decade of the past 500 years in central Europe, according to scPDSI from OWDA it was the ninth driest decade, despite quite important spatial differences in the occurrence of drier and wetter areas between both reconstructions. From the analysis it follows that particularly the summers of 1534, 1536, 1538 and 1540 were dry not only in central Europe, but also over greater parts of western Europe.
Can SDG Acceleration Actions promote the key SDGs?
Authors: Hua Ting , Zhao Wenwu
Published: March 2020

Through the promotion of the past five years, some positive signs have emerged in the progress of some SDGs. However, there is still a large gap between the speed and scale of sustainable transition compared to the extent needed to achieve the SDGs in 2030. United Nations has called on governments and international organizations to propose appropriate SDGs Acceleration Actions to reverse the current unfavorable situation. But before moving forward to more actions, it is important to know which SDGs are urgently needed to be addressed and the matching between the existing actions and priority needs. In this study, we attempt to reveal the SDGs that need to be focused on in promoting SDG Acceleration Actions in terms of expert inquiries, the current sustainable development level, the relationship among 17 SDGs, and the comparison between planetary boundaries and SDGs. We found that there is an obvious conflict between the boost of the SDGs and the control of the biophysical boundaries. And if considering achieving sustainability within the planetary boundaries, we should focus on SDG2, SDG9, SDG14, SDG15, the conflict between these SDGs and multiple biophysical indicators such as CO2 emissions needs to be reconciled, and the gap between average and highest efficiency utilization efficiency needs to be narrowed. Compared to our results, existing actions are not enough for the key SDGs we screened. This study could be a step forward to optimizing the overall arrangement of SDG Acceleration Actions and implementing SDG policy effectively.

Keywords: Sustainable Development Goals (SDGs); SDGs Acceleration Actions; Planetary Boundaries; Sustainability
3D basin and petroleum system modelling in the North Sea Central Graben - a Dutch, German, Danish cross-border study
Authors: Lutz Rüdiger , Arfai Jashar , Nelskamp Susanne , Mathiesen Anders , Schovsbo Niels Hemmingsen , Ladage Stefan , Britze Peter , Stewart Margaret
Published: March 2020

A Geological Analysis and Resource Assessment of selected Hydrocarbon Systems (GARAH) is carried out as part of the overarching GeoERA project. Here, we report first results of a 3D basin and petroleum system model developed in a cross-border area of the Dutch, Danish and German North Sea Central Graben area. This pilot study reconstructs the thermal history, maturity and petroleum generation of potential Lower, Middle and Upper Jurassic source rocks. The 3D pilot study incorporates new aggregated and combined layers from the three countries. Results of the study feed back into the 3DGEO-EU project of GeoERA.

Eight key horizons covering the whole German Central Graben and parts of the Dutch and Danish North Sea Central Graben were selected for building the stratigraphic and geological framework of the 3D basin and petroleum system model. The model includes depth and thickness maps of important stratigraphic units as well as the main salt structures. Petrophysical parameters, generalized facies information and organic geochemical data from well reports are assigned to the different key geological layers. The model is further calibrated with temperature and maturity data from wells of the three countries and from publications. The time span from the Late Permian to the Present is represented by the model including the most important erosional phases related to large-scale tectonic events during the Late Jurassic to Late Cretaceous. Additionally, salt movement through time expressed as diapirs and pillows is considered within the 3D basin and petroleum system model.

This is a part of an ongoing EU Horizon 2020 GeoERA project (The GARAH, H2020 grant #731166 lead by GEUS).
Fast Magnetic Reconnection by Turbulence with High Landquist Number
Authors: Yang Liping , Li Hui , Guo Fan , Li Xiancan , Li Shengtai , Zhang Lei , He Jiansen , Feng Xueshang
Published: March 2020

We report detailed numerical studies of magnetic reconnection in high-Lundquist-number, turbulent plasma by means of a three-dimensional (3D) resistive magnetohydrodynamics model. It is found that although turbulence is pre-existing, magnetic ﬁelds still restructure themselves to shape many X-points with evident mean inﬂow/outﬂow as well as the hierarchically generated magnetic ﬂux ropes (plasmoids in 2D) with twist ﬁeld lines. Moreover, the turbulence facilitates magnetic reconnections, and makes the normalized global reconnection rate reach ∼ 0.02 − 0.1, corresponding to turbulence level from very low to high and magnetic energy release from feeble to violent. The rate is nearly independent on the Lundquist number, and thus the fast turbulent reconnection occurs. A stochastic separation of the reconnected magnetic ﬁeld lines with large opening angles follows a super-diﬀusion, indicating the broadening of outﬂow regions owing to the turbulence. These ﬁndings manifest that with the high Lundquist numbers (S ≥ 10^4), the 3D reconnection is turbulent and fast.
Carbon-rich composition of the icy moons of Jupiter and Saturn, and asteroid 1-Ceres
Authors: Reynard Bruno , Neri Adrien , Guyot François , Sotin Christophe
Published: March 2020

The inner structure of icy moons comprises ices, liquid water, a silicate rocky core and sometimes an inner metallic core depending on thermal evolution and differentiation. Mineralogy and density models for the silicate part of the icy satellites cores were assessed assuming a carbonaceous chondritic (CI) bulk composition and using a free-energy minimization code and experiments [1]. Densities of other components, solid and liquid sulfides, carbonaceous matter, were evaluated from available equations of state. Model densities for silicates are larger than assessed from magnesian terrestrial minerals, by 200 to 600 kg/m3 for the hydrated silicates, and 300 to 500 kg/m3 for the dry silicates, due to the lower iron bulk concentration in terrestrial silicates as a lot of iron is segregated in the core.

We find that CI density models of icy satellite cores taking into account only the silicate and metal/sulfide fraction cannot account for the observed densities and reduced moment of inertia of Titan and Ganymede without adding a lower density component. We propose that this low-density component is carbonaceous matter derived from insoluble organic matter, in proportion of ~30-40% in volume and 15-20% in mass. This proportion is compatible with contributions from CI and comets, making these primitive bodies including their carbonaceous matter component likely precursors of icy moons, and potentially of most of the objects formed behind the snow line of the solar system. Similar conclusions are reached for 1-Ceres when applying this compositional model, with even higher carbon content of the order of 25±5wt% in line with independent estimates [2]. It suggests that the building materials are similar for asteroid 1-Ceres and the icy moons of giant planets.

 

[1]Neri et al., Earth Planet Sci Letters, 530 (2020) 115920

[2]Zolotov, Icarus, 335 (2020) 113404
First Ocean Bottom Seismometer network underneath the ice-covered Arctic Ocean: Operational challenges and chances for monitoring the state of the sea ice cover
Authors: Vera Schlindwein , Henning Kirk , Marc Hiller , John-Robert Scholz , Mechita Schmidt-Aursch
Published: March 2020

Active and passive seismic monitoring of the cryosphere is mostly done with land seismometers on the surface of ice masses. Seismic monitoring beneath sea ice at the bottom of ice covered oceans has hardly been attempted, because ocean bottom seismometers (OBS) are difficult to recover in perennial sea ice. As a result, for example the tectonic activity of the Arctic mid-ocean ridge system is poorly known. Recently, the ambient seismic noise in long-term seismic records proved a useful tool to monitor the state of the sea ice cover. Since sea ice effectively dampens the formation of wave action, the power in the microseismic noise band, that is mostly generated by ocean wave action, shows seasonal variations which can be explored to study ocean wave climate in relation to the sea ice cover.

From September 2018 - September 2019, we deployed for the first time a network of 4 broadband ocean bottom seismometers at distances of about 10 km at a water depth of roughly 4 km near Gakkel Deep on eastern Gakkel Ridge, Arctic Ocean, from board RV Polarstern. We modified the Lobster-type OBS to include a Posidonia transponder that allowed to accurately track the OBS during descent and ascent and when surfacing underneath an ice floe. We then carefully broke the ice floes until the OBSs appeared in open water and could be recovered.

The network was designed to record local earthquakes along Gakkel Ridge, but it also yields valuable year-round data on the microseismic noise signal at the bottom of the Arctic Ocean in a marginal ice zone.

A first inspection of the data shows a clearly reduced power in the microseismic noise band compared to the Norwegian-Greenland Sea and strongly time dependent noise levels, that may potentially be related to temporary wave action when sea ice retreats during summer. However, the modified OBS structure with a large head buoy fixed to the OBS structure may also be prone to vibrations caused by ocean bottom currents. We will present an initial analysis of the seasonal evolution of the ambient seismic noise that will help to discriminate noise sources and evaluate the potential of such records to monitor the state of the sea ice cover.
Catchment-scale connection between vegetation accessible storage and satellite-derived Soil Water Index
Authors: Bouaziz Laurène , Steele-Dunne Susan , Schellekens Jaap , Weerts Albrecht , Stam Jasper , Sprokkereef Eric , Winsemius Hessel , Savenije Hubert , Hrachowitz Markus
Published: March 2020

Estimates of water volumes stored in the root-zone of vegetation are a key element controlling the hydrological response of a catchment. Remotely-sensed soil moisture products are available globally. However, they are representative of the upper-most few centimeters of the soil. For reliable runoff predictions, we are interested in root-zone soil moisture estimates as they regulate the partitioning of precipitation to drainage and evaporation. The Soil Water Index approximates root-zone soil moisture from near-surface soil moisture and requires a single parameter representing the characteristic time length T of temporal soil moisture variability. Climate and soil properties are typically assumed to influence estimates of T, however, no clear quantitative link has yet been established and often a standard value of 20 days is assumed. In this study, we hypothesize that optimal T values are linked to the accumulated difference between precipitation (water supply) and evaporation (atmospheric water demand) during dry periods with return periods of 20 years, and, thus, to catchment-scale vegetation-accessible water storage capacities. We identify the optimal values of T that provide an adequate match between estimated SWI from several satellite-based near-surface soil moisture products (derived from AMSR2, SMAP and Sentinel-1) and modeled time series of root-zone soil moisture from a calibrated process-based model in 16 contrasting catchments of the Meuse river basin. We found that optimal values of T vary between 1 and 98 days with a median of 17 days across the studied catchments and soil moisture products. We furthermore show that T, which was previously known to increase with increasing depth of the soil layer, is positively and strongly related with catchment-scale root-zone water storage capacity, estimated based on long-term water balance data.  This is useful to generate estimates of root-zone soil moisture from satellite-based surface soil moisture, as they are a key control of the response of hydrological systems.
GLORIA observations of pollution tracers C2H6, C2H2, HCOOH, and PAN in the North Atlantic UTLS region
Authors: Wetzel Gerald , Friedl-Vallon Felix , Glatthor Norbert , Grooß Jens-Uwe , Gulde Thomas , Höpfner Michael , Johansson Sören , Khosrawi Farahnaz , Kirner Oliver , Kleinert Anne , Kretschmer Erik , Maucher Guido , Nordmeyer Hans , Oelhaf Hermann , Orphal Johannes , Piesch Christof , Sinnhuber Björn-Martin , Ungermann Jörn , Vogel Bärbel
Published: March 2020

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an imaging Fourier transform spectrometer (iFTS) using a 2-dimensional detector array to record emission spectra in the mid-infrared region with high spatial resolution. GLORIA is operated on high altitude research aircraft, mainly in the limb observational geometry to measure vertical profiles of temperature and atmospheric trace species with high vertical resolution.

In autumn 2017, the Wave-driven ISentropic Exchange (WISE) aircraft campaign took place from Shannon (Ireland). Sixteen flights with the High Altitude and Long Range Research Aircraft (HALO) were performed between 31 August and 21 October 2017 over the eastern North Atlantic region.

GLORIA observations were analysed with regard to pollutant species like C2H6, C2H2, HCOOH, and PAN, which are produced at distinct source regions near the ground and transported to remote regions due to their atmospheric lifetime of several weeks. Enhanced volume mixing ratios of these molecules were detected along some parts of the flight track in the upper troposphere and lowermost stratosphere (UTLS).

Measured profiles of these species are compared to simulations from the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and reanalysis data from the Copernicus Atmosphere Monitoring Service (CAMS). Furthermore, emission tracers and back-trajectories from the Chemical Lagrangian Model of the Stratosphere (CLaMS) are used to analyse the source regions of these pollution events.
Representative meat consumption pathways for sub-Saharan Africa and their local and global energy and environmental implications
Authors: Falchetta Giacomo , Golinucci Nicolò , Noussan Michel
Published: March 2020

In sub-Saharan Africa (SSA) most people live on plant-dominated diets, with significantly lower levels of per-capita meat consumption than in any other region. Yet, economic development has nearly everywhere spurred a shift to dietary regimes with a greater consumption of meat, albeit with regional heterogeneity for meat-type and magnitude. A growing regional economy, changing cultural attitudes, and a steeply increasing population could thus push the regional demand upward in the coming decades, with significant depletion of regional and global natural resources and environmental repercussions. We study the historical association of the four main meat types with demand drivers in recently developed countries via seemingly unrelated regression (SUR) equation systems. Using the calibrated coefficients, trajectories of meat consumption in SSA to 2050 are projected relying on the SSP scenarios over GDP and population growth. Then, using a Leontiefian environmentally extended input-output (EEIO) framework exploiting the EXIOBASE3 database, we estimate the related energy, land, and water requirements, and the implied greenhouse gas (CO2, CH4, N2O) emissions. We calculate that if production to meet those consumption levels takes place in the continent – compared to the current situation – global greenhouse gas (GHG) emissions would grow by 230 Mt CO2e (4.4% of today’s global agriculture-related emissions), the land required for cropping and grazing would require additional 4.2 · 106 km2 (more than half of the total arable land in SSA), total blue water consumption would rise by 10,300 Mm3 (0.89% of the global total), and additional 1.2 EJ of energy (6% of today’s total primary energy demand in the region) would be required. Alternative scenarios where SSA is a net importer of final meat products are reported for comparison. The local policy and attitudes towards farming practices and dietary choices will have significant impact on both the regional environment and global GHG emissions.
Evidence of uplift at Argentière glacier (Mont Blanc area, France)
Authors: Vincent Christian , Walpersdorf Andrea , Gilbert Adrien , Gagliardini Olivier , Gimbert Florent , Gillet-Chaulet Fabien , Piard Luc , Jourdain Bruno , Cusicanqui Diego , Moreau Luc , Laarman Olivier , Six Delphine
Published: March 2020

Understanding basal processes is a prerequisite for predicting the overall motion of glaciers and its response to climate change. Although a number of studies have shown that subglacial hydrology affects glacier’s basal sliding motion, the involved mechanisms remain poorly known. Several studies suggested that glacier velocity increases with englacial and subglacial water storage, but observational quantification of subglacial water storage and associated velocity changes are challenging to make due to uncertainties on velocity measurements and on vertical straining.

Here we tackle this observational challenge through analyzing numerous field measurements from the surface and from the subglacial observatory on the Argentière Glacier (French Alps). We analyze specifically the relationships between daily sliding velocities (measured continuously at the glacier base), surface horizontal and vertical velocities from DGPS observations and ice thickness changes over years 2018 and 2019. We find strong upward surface movements of about 0.5 m during the winter until the beginning of May that cannot be explained by longitudinal strain rate changes. We support that it is caused by water volume increase in subglacial cavities.

Further analyzing the relationships between cavity growth, sliding and surface velocities, we find that unlike in previous studies bed separation variations are not synchronous with sliding speed variations. Surface uplift starts in winter, which is long before the spring sliding acceleration, and surface drop occurs mid-summer, which is long before the end of summer sliding deceleration. These findings support that the link between subglacial water storage and sliding speed may not be as direct as previously thought.
Linking glacier surface changes to subglacial conduit locations for a temperate Alpine glacier
Authors: Egli Pascal , Belotti Bruno , Sala Martino , Lane Stuart , Irving James
Published: March 2020

It is well understood that topography near the snout of an alpine glacier may evolve quickly due to differential melting depending on exposure to solar radiation and on debris cover thickness. However, the positioning and shape of subglacial conduits underneath shallow ice may also have an important influence on ice creep and thereby on the topography of this region. This relationship could potentially be used to determine locations of subglacial conduits via the detailed observation of glacier surface changes.

We monitored the ice-marginal zone of the Otemma Glacier in the south-western Swiss Alps with daily UAV surveys at high spatial resolution and with a network of ablation stakes over a period of three weeks. After subtraction of melt measured with ablation stakes, we produced maps of changes in ice surface topography that are due to processes other than melt. In two consecutive summers we conducted three-dimensional GPR surveys in the same area of interest. By looking at these spatially dense grids of GPR measurements, we are able to identify the locations and shape of sub-glacial conduits underneath the ice marginal glacier tongue, for ice thicknesses between 20 m and 50 m. Superposition of the GPR-derived channel maps with those showing the topographic changes suggest a correlation between ice surface changes and processes operating at the glacier bed.
IWV retrieval from ground and shipborne GPS receivers during NAWDEX
Authors: Bosser Pierre , Olivier Bock , Nicolas Laurain
Published: March 2020

For the documentation of time and space variations of water vapor in atmosphere during the Nawdex campaign (North Atlantic, Autumn 2016), a ground network of more than 1200 coastal continuously operation reference GNSS stations has been analyzed. This network spreads from Caribbeans to Morocco through Greenland. Retrieved IWV have been used to evaluate ERAI and ERA5 reanalysis and highlight improvements made by ERA5 (-0.2 +/- 1.6 kg/m2 vs -0.3 +/- 2.1 kg/m2 overall). They are also used to describe high impact weather events that took place during the experiment.

The analysis of this ground GNSS network has been completed with the IWV retrieved from GPS data acquired by the French RV Atalante which cruises in the area during the experiment. IWV from shipborne receiver are consistent with both ERAI and ERA5 reanalysis (1.0 +/- 3.2 kg/m2 and 1.3 +/- 2.0 kg/m2 respectively) ; shipborne IWV also agree with IWV from nearby ground GNSS stations (-0.4 +/- 0.9 kg/m2). These results confirm the quality of shipborne IWV retrievals and opens up prospects for use in climatology and meteorology.
The CRPS – used as a robust objective function for groundwater model calibration in light of observation and model structural uncertainty
Authors: Schneider Raphael , Henriksen Hans Jørgen , Stisen Simon
Published: March 2020

The Continuous Ranked Probability Score (CRPS) is a popular evaluation tool for probabilistic forecasts. We suggest using it, outside its original scope, as an objective function in the calibration of large-scale groundwater models, due to its robustness to large residuals in the calibration data.

Groundwater models commonly require their parameters to be estimated in an optimization where some objective function measuring the model’s performance is to be minimized. Many performance metrics are squared error-based, which are known to be sensitive to large values or outliers. Consequently, an optimization algorithm using squared error-based metrics will focus on reducing the very largest residuals of the model. In many cases, for example when working with large-scale groundwater models in combination with calibration data from large datasets of groundwater heads with varying and unknown quality, there are two issues with that focus on the largest residuals: Such outliers are often i) related to observational uncertainty or ii) model structural uncertainty and model scale. Hence, fitting groundwater models to such deficiencies can be undesired, and calibration often results in parameter compensation for such deficiencies.

Therefore, we suggest the use of a CRPS-based objective function that is less sensitive to (the few) large residuals, and instead is more sensitive to fitting the majority of observations with least bias. We apply the novel CRPS-based objective function to the calibration of large-scale coupled surface-groundwater models and compare to conventional squared error-based objective functions. These calibration tests show that the CRPS-based objective function successfully limits the influence of the largest residuals and reduces overall bias. Moreover, it allows for better identification of areas where the model fails to simulate groundwater heads appropriately (e.g. due to model structural errors), that is, where model structure should be investigated.

Many real-world large-scale hydrological models face similar optimizations problems related to uncertain model structures and large, uncertain calibration datasets where observation uncertainty is hard to quantify. The CRPS-based objective function is an attempt to practically address the shortcomings of squared error minimization in model optimization, and is expected to also be of relevance outside our context of groundwater models.
Uranium isotope systematics in the Melchsee-Frutt cave region (Central Swiss Alps)
Authors: Schröder-Ritzrau Andrea , Fohlmeister Jens , Trüssel Martin , Förstel Julius , Frank Norbert , Spötl Christoph , Luetscher Marc
Published: March 2020

We investigated the uranium isotope systematics in an alpine cave environment (central Switzerland). We measured the U concentration and the 234U/238U activity ratio of the two main host rock formations in which the cave developed and the 234U/238U activity ratio of drip water. We further investigated the U characteristics of young carbonate precipitates (< 500 a old) at these drip sites. In addition, we analysed several speleothems between 1 and ~200 ka old. We observe variable U concentrations (between 0.1 – 5 ppm) and a significant spread in the initial activity ratio of 234U/238U (between ~1 and 5) between individual drips and individual stalagmites. In general, high U concentrations are accompanied by low initial 234U/238U ratios and vice versa. However, these data do not follow a binary mixing line between the two host rock endmembers (both show low U concentrations of about 1 ppm). Instead, we argue that redox processes within the karst might govern the U systematics of cave drip water and speleothems, as high and variable SO42- concentrations in drip water are observed, which point to at least locally constrained anoxic conditions in the host rock. The dependence of the initial 234U/238U activity ratio and U concentration of the stalagmites from this cave in concert with the partly large absolute value in their initial activity ratio open the perspective for dating speleothems from this karst region back to ~1 Ma.
TRACMASS - A mass conserving trajectory code for ocean and atmosphere general circulation models
Authors: Aldama Campino Aitor , Döös Kristofer , Berglund Sara , Dey Dipanjan , Kjellsson Joakim , Jonsson Bror
Published: March 2020

We present the latest version of the TRACMASS trajectory code, version 7.0. The new version includes new features such as water tracing in the atmosphere, parameterisation scheme for sub-grid scale turbulence, generalisation of the tracer handling, etc. The code has also become more user friendly and easier to get started with. Previous versions of TRACMASS only allowed temperature, salinity and potential density to be calculated along the trajectories, but the new version allows any tracer to be followed e.g. biogeochemical tracers or chemical compounds in the atmosphere. The new parameterisation of sub-grid turbulence will enhance the kinetic energy and dispersion of trajectories in the ocean so that results from eddy-permitting ocean models (dx ∼25km) resemble those from “eddy-resolving” models (dx ∼8km). We will demonstrate some use cases of these new capabilities for atmosphere and ocean sciences. 

TRACMASS calculates Lagrangian trajectories offline for both the ocean and atmosphere by using already stored velocity fields, and optionally tracer fields. The velocity fields may be taken from ocean or atmosphere circulation models (e.g. NEMO, OpenIFS), reanalysis products (e.g. ERA-5) or observations (e.g. geostrophic currents from satellite altimetry). The fact that the numerical scheme in TRACMASS is mass conserving allows us to associate each trajectory with a mass transport and calculate the Lagrangian mass transport between different regions as well as construct Lagrangian stream functions. 

A live demonstration on how to set up, configure and run the TRACMASS code will be given.
Porosity of metamorphic rocks and fluid migration within subduction interfaces
Authors: Reynard Bruno , Ganzhorn Anne-Céline , Pilorgé Hélène
Published: March 2020

            Large earthquakes break the subduction interface to depths of 60 to 80 km. Current models hold that seismic rupture occurs when fluid overpressure builds in link with porosity cycles, an assumption still to be experimentally validated at high pressures. Porosities of subduction zone rocks are experimentally determined under pressures equivalent to depths of up to 90 km with a novel experimental approach that uses Raman deuterium-hydrogen mapping. Natural rocks (blueschists, antigorite serpentinites, and chlorite-schists) representing a typical cross-section of the subduction interface corresponding to the deep seismogenic zone are investigated. In serpentinite, and to a smaller extent blueschist, porosity increases with deformation, whereas chlorite-rich schists remain impermeable regardless of their deformation history[ 1]. Such a contrasting behavior explains the observation of over-pressurized oceanic crust and the limited hydration of the forearc mantle wedge. These results provide quantitative evidence that serpentinite, and likely blueschist, may undergo porosity cycles making possible the downdip propagation of large seismic rupture to great depths. 

[1] Ganzhorn, A.C., Pilorgé, H., Reynard, B., 2019, Earth and Planetary Science Letters, 522: 107-117.
Examining the extremal dependence structure of precipitation in Norway
Authors: Vandeskog Silius Mortensønn , Martino Sara
Published: March 2020

Extreme precipitation can lead to great floods and landslides and cause severe damage and economical losses. It is therefore of great importance that we manage to assess the risk of future extremes. Furthermore, natural hazards are spatiotemporal phenomena that require extensive modelling in both space and time. Extreme value theory (EVT) can be used for statistical modelling of spatial extremes, such as extreme precipitation over a catchment. An important concept when modelling a natural hazard is the degree of extremal dependence for the given phenomenon. Extremal dependence describes the possibility of multiple extremes occurring at the same time. For the stochastic variables X and Y, with distribution functions FX and FY, the measure

χ = limu→1 P(FX(X) > u Ι FY(Y) > u)

describes the pairwise extremal dependence between X and Y. If χ = 0, then the variables are asymptotically independent. If χ > 0, they are
asymptotically dependent. Thus, extremes tend to occur simultaneously in space for processes that are asymptotically dependent, while this seldom occurs for asymptotically independent processes. It is a general belief that extreme precipitation tends to be asymptotically independent. However, to our knowledge, not much work has been put into analysing the extremal dependence structure of precipitation. Different statistical models have been developed, which can be applied for modelling spatial extremes. The most popular model is the max-stable process. Unfortunately, this model does not provide a good fit to asymptotically independent processes. Other models have been developed for better incorporating asymptotic independence, but most have not been extensively applied yet. We aim to examine the extremal dependence structure of precipitation in Norway, with the ultimate goal of modelling and simulating extreme precipitation. This is achieved by examining multiple popular statistics for extremal dependence, as well as comparing different spatial EVT models. This analysis is performed on hourly, gridded precipitation data from the MetCoOp Ensemble Prediction System (MEPS), which is publicly available from the internet: http://thredds.met.no/thredds/catalog/meps25epsarchive/catalog.html.
Simulation of brine migration along geological fault zones using a consistent mesh approach
Authors: Vehling Falko , Gasanzade Firdovsi , Delfs Jens-Olaf , Bauer Sebastian
Published: March 2020

Upward brine migration through permeable fault damage zones could endanger near-surface drinking water resources. Deep porous rock formations offer a large potential for gas storage, like e.g. methane or CO2. But gas injection induces formation pressure build up, that can potentially lead to vertical or horizontal brine displacement. Here fault zones play an important role as they can act either as lateral no-flow boundaries or as permeable pathways, that allow for fluid flow and pressure dissipation. Numerical reservoir simulations, which have become an important tool for investigating these effects quantitatively, have to be performed on a regional scale, in order to include the large-scale geological faults zones. Fault zones have to be implemented into the model in a geometrically and hydraulically flexible way, to account for the variety of natural conditions encountered, as e.g. open or closed fault zone.

In order to model that complexity, the corner point grid approach has been applied by geologists for decades. The corner point grid utilizes a set of hexahedral blocks to represent geological formations. At the fault plane, where geological layers are vertically shifted, hanging nodes appear and the corner point grid cannot be used directly, if permeable fault zones have to be represented in the model. In this study we present an extension of a mesh converter, which removes hanging nodes at the fault plane by point combination, thus providing a consistent finite element mesh. Our numerical model can account for heterogeneous hydraulic properties of the fault damage zone and the enclosed fault core. The fault core is represented by one layer of 3D finite elements on each side of the fault plane. The fault damage zone consists of a continuous layer of quadrangular 2D finite elements, which are attached at the outer face of the 3D fault core elements. This model allows for fluid flow along the fault plane while fluid flow through the fault core could be adjusted by element permeability. This concept was implemented into a workflow using the FEM-simulator OpenGeoSys in combination with a mesh converter.

The concept and workflow are shown to run stable using dedicated test cases for method validation, accounting for the coupled transport of water, heat and salt mass for different fault zone setups in a synthetic multi-layered subsurface. Here we focused on brine displacement and uprising due to formation pressure increase after gas injection, which is numerically realized by Dirichlet pressure boundary conditions. Further, we will investigate the relation between computational efficiency and flow solution differences by comparing this concept with the approach of fully discretized faults. Additionally, we will apply our workflow on a real geological case in the Northern German Basin, where a fault system is close to a potential gas storage side.  
The Method of Curvature Attribute applied in the Depth Inversion of the Geological Bodies Edge by Potential Field Data
Authors: Liu Jinlan , Wang Wanyin , Xiong Shengqing
Published: March 2020

It is vital to quickly and effectively determine the extent and depth of geological body by using potential field data in gravity and magnetic survey. In this study, three key techniques studying the extent and depth of geological sources based on curvature attribute are studied: the optimal solutions to the objective function, the edge of geological bodies and picking out solutions. Firstly, the optimal solution to the objective function is studied, that is, the key extraction algorithm about the curvature attribute. The Huber norm is introduced into the extraction algorithm of curvature attribute, which more accurately detect the depth of edge of the geological bodies. Secondly, the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique is introduced into curvature attribute, which shows more continuous results about the edge position of the geological bodies and more sensitive to the small-scale tectonic structure. Finally, we study the way to pick out the inversion solution, that is, to solve the multi-solution equations in the inversion. The upward continuation of a certain height with strict physical significance was introduced into the inversion method, which was used to suppress the noise, and the final and actual inversion depth was equal to the inversion depth minus the height of upward continuation. And the average value of threshold limitation technology of the potential fields data was also introduced into this method. Using the two technologies, solutions of non-field source edge positions were eliminated, and make the inversion solutions closer to the actual situation. Through the above three key techniques, the accuracy, continuity and recognition to the small-scale structure of the inversion result are optimized. The theoretical models are used to verify the effectiveness of the above key technologies, the results show that the three key technologies have achieved good results, and the combined models are used to verify the effectiveness of the optimized inversion method. The measured aeromagnetic data were used to inversing the edge depth of the intrusive rock in a mining area, and the inversion results are in good agreement with the rock depth revealed by borehole.