bluuebunny/crossref_metadata_2025 huggingface dataset:
Microplastics: Are they really a threat to groundwater systems?
Authors: Ameen Ahmad , Stevenson Margaret , Blaschke Alfred Paul
Published: March 2020

Recently, global annual plastics production has reached a record of 359 million tonnes and in Europe nearly 62 million tonnes, with only a small portion (6-26%) being recycled. Plastic debris released into the environment are categorized, according to size, as macroplastics (> 5mm), microplastics (0.1μm - 5mm) and nanoplastics (< 0.1μm). Microplastics are now recognized as an emerging pollutant due to their abundance in natural environments, and because of growing concerns, the United Nations Environment Programme (UNEP) has included it in the list of top 10 environmental problems.

Additionally, microplastics have a tendency to act as a vector for other contaminants such as pathogens, organic pollutants and heavy metals due to strong dispersion and diffusion mechanisms. The majority of ongoing research on microplastics has primarily focussed on marine systems, but land surface contamination may also be important due to observed release rates that are approximately 20 times higher, in comparison to oceans. Nevertheless, only a few studies have addressed the presence of microplastics in soil and groundwater.

A research gap exists regarding the physical and chemical mechanisms that govern microplastic transport and retention in groundwater. Therefore, a study is being conducted to investigate the distribution, fate and transport of microplastics through groundwater. The overall aim is to improve the understanding of the transport mechanisms of these emerging pollutants and if they enhance the mobility of microbial communities. This research has two main objectives: firstly, to simulate the transport behaviour of various kinds of microplastics (different types, shapes, sizes, and surface morphology), secondly, to analyse the microplastics as potential vectors for microorganisms.

The key factors that are affecting the transport of different sized microplastics will be addressed. Additionally, the co-transport of microorganisms with microplastics during their movement within soil and groundwater will also be considered.
Graphitic material in fault zones: Implication for strain localization and rheological weakening
Authors: Cao Shuyun , Neubauer Franz , Lv Meixia
Published: March 2020

Graphitic carbon exhibits a large range of structures and chemical compositions, from amorphous-like compounds to crystalline graphite. The graphitic carbon-bearing rocks are widely occurred in low- to high- grade metamorphic massif and fault zone. The carbonaceous material in the rock will gradually transform from an amorphous into an ordered crystalline structure by thermal metamorphism, which is called graphitization. The degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock. In many low-grade metamorphic rocks, graphitic carbon (e.g., soot, low-grade coal) is often associated with brittle fault gouge whereas in high-grade metamorphic rocks, graphitic carbon (crystalline granite) are most commonly seen in marble, schist or gneiss. In recent years, graphitic carbon-bearing rocks have been reported from natural fault zones (reviwers paper see Cao and Neubauer 2019 and references therein). The graphitic carbon grains in our samples tend to enrich in slip-surface or micro-shear zone with strain localization in fault, performed as dislocation glide of deformation. The graphite LPO shows slip system in the direction of basil  combined basil  slip and weak prism  slip systems, suggesting a low-temperature to a medium to high temperature deformation conditions, which is in consistent with the results of Raman Spectra of Carbonaceous material (RSCM) thermometry. We also proposed that the graphitic carbon formed in the rocks can significantly affect the mechanical properties of the fault during the process of faulting. This process can effectively cause reaction weakening and strain localization, which is thought to play an important role as solid lubrication in fault weakening.
Future wind energy resources in the North Sea as predicted by CMIP6 models
Authors: Hahmann Andrea N. , Peña Alfredo , Pryor Sara C. , Luzia Graziela
Published: March 2020

Net carbon dioxide emissions have to be brought down to zero in the coming decades to hold the rise in global temperature in this century below the 2°C from pre-industrial levels. This target implies a fundamental transformation of the global energy system that will have to rely heavily on renewable energy sources. Among these, the harvesting of electricity from the wind plays an important role. Yet, climate change itself can impact the supply of renewable energy. Therefore, national climate mitigation plans need to make informed decisions regarding any changes to future extractable wind resources to consider the possible risks.

In this work, we explore the changes in wind climatology over the North Sea in the different shared socioeconomic pathways (SSP) emission scenarios as identified by the output of a selection of CMIP6 simulations. Many northern European countries rely on the wind resources of the North Sea for climate mitigation. As a first step, however, we validate various aspects of the wind speed and direction and their variability in the historical CMIP6 simulations as compared to multiple long-term reanalyses. The work also includes calculations of annual energy production for existing and planned wind farms in the North Sea and how these could change in the coming decades.
First quantitative evidences of ghost-rock karstification controlling regional karst geometry
Authors: Vernant Philippe , Malcles Oswald , Ritz Jean-François , Fink David , Cazes Gaël , Fujioka Toshiyuki , Chéry Jean
Published: March 2020

Although more and more processes are discussed and discovered on the genesis and evolution of cave systems, the tiered karsts are often explained by a control of the base level evolution. In this classical model, the horizontal galleries are explained by a stability of the base level elevation. To the contrary, the shafts and network segments with steep slopes are related to incision periods with a base level lowering.

We use Terrestrial Cosmogenic Nuclide Geochronology to estimate burial ages of alluvium trapped in several caves of the Larzac plateau in Southern France. All the samples are collected in horizontal cave levels, sometimes located between steeper segments. Some caves are opened in river gorge walls, while others are located below the Larzac plateau not farther than 5km away from the river gorges.

The burial ages for the caves opening in the gorges are consistent with the incision rates given for the area and could be interpreted using the classical model. However, the cave within the plateau show a horizontal level with alluvium deposited 200m above the caves in the gorge with the same burial ages (~1 Myr). Since then, new shafts have been opened without alluvium and are hydrologically connected to the river by deeper[jfr1]  hypogenic galleries. The cave morphologies and the geochronological data suggest that the classical model fails to explain the horizontal levels in cave below the plateau. We postulate that the geometry of the caves in these limestone and dolomite plateaus are related to a previous period of ghost-rock and alteration roots formations. Without the opening of an efficient connection between this primokarst and the valley, no alluvium can flow through the cave. Therefore, we think that our burial ages constrain the emptying of the ghost-rocks leading to the genesis of the cave where water and possibly alluvium can flow through. Furthermore, these new finding explain why the horizontal levels in the caves are not clearly related to horizontal markers in the surface geomorphology and why large shafts (>100m) exist in the area without evidences of long periods of base level stability followed by large drop of the regional base level.

 
Numerical modeling of attenuation and non linear effects in computational seismology
Authors: Asfour Kassem , Martin Roland , El Baz Didier
Published: March 2020

We solve elastic waves equations in 2D/3D using a fourth order in time and space finite volume method based on exact Riemann solver and wave limiters and designed particularly to capture shock waves.  We validate our code by comparing our results with spectral elements solutions (SPECFEM). 

 

The goal is to detect the levels of fluid saturations in complex rheological media at different scales (near surface or crustal scale) by homogenizing the rheological laws for different frequency contents of the signal sources. For this purpose, at high frequencies, attenuation and/or non linear effects must be added to the stress-strain relations that affect the apparent/effective seismic wave velocities due to unconsolidated, granular or damaged and fractured nature of solid media.

 

In our present studies, we show first how we include the viscoelastic models using auxiliary differential equation approach as in Martin et al. 2019. Then, we show at two different scales (laboratory and natural near surface) how we are able to reproduce real seismic data for granular and porous media in the range of 300-4000 Hz for a 1m configuration experimental setup and how the attenuation and homogeneized seismic velocities of the porous matrix correlate to gravity laws and can explain the recorded signals. Recorded signals are compared to the numerical solutions for three different vertical pore pressure gradients due to the injection of gas.  

 

After validating the code on this controlled experiment we extend our methods at the scale of a 100m natural site in the Orgeval basin in the Parisian region/ France where we want to model the variations of the seismic velocities in the first tens of meters close to the near surface due to the presence of water contents. The idea is to be able to monitor the fluid contents of the ground in the neighborhood of the rivers and the fluid exchanges between nappes, rivers and the underground at the different periods of time (weekly, monthly and annualy). The Vp/Vs ratios reaching high values around 2 due to the water presence, and the Vp and Vs models being obtained by ray-tracing based first arrival time inversions.

The data are provided by the PIREN-Seine program in the last three years.

 

Complex non-linearity responses of the medium  can be modelled with our codes and also be extended to  damaged faults that can be activated and trigger earthquakes due to bulk and shear moduli decrease.

 
Heavy metals removal by flax fibers to a further use in urban runoff management systems
Authors: Kajeiou Meriem , Alem Abdellah , Pantet Anne , Mezghich Soumaya , Ahfir Nasre-Dine
Published: March 2020

Abstract

Water pollution has long been considered a major problem causing environmental and public health issues. A range of contaminants are encountered in wastewater, industrial effluents and also road runoff, they include total suspended solids, nutrients, hydrocarbons and heavy metals. These latter have been found very toxic and hazardous, either for human health, or fauna and flora. In recent decades, studies have demonstrated a good removal efficiency of heavy metals by adsorption technique, and especially biosorption. Numerous biosorbents have been investigated, mainly lignocellulosic materials which have shown high adsorption capacity. Within this context, this study aims to investigate flax fibers capacity of zinc, copper and lead ions removal from aqueous solutions, in order to examine the best conditions to test a full-scale device designed to treat stormwater runoff. The choice of flax is related to its high availability, low cost and local economy reasons. The device consists of sand and layers of flax fibers geotextiles. It will be placed on a parking at the entrance of a retention basin in Le Havre. For this purpose, batch experiments were carried out with ternary and mono-metal solutions of zinc, copper and lead ions at room temperature with molar concentrations of 0.04 mmol.l-1, at pH around 6.4. Biosorption kinetics and biosorption equilibrium were performed and analyzed. The results showed a favorable adsorption for the three metals in the order Pb > Cu > Zn for both types of solutions, with adsorption rates of 94%, 75% and 62% respectively in the ternary metal solution and 94%, 81% and 82% in the mono-metal solutions. The effect of competition was important for zinc, barely visible for copper, and non-existent for lead.

Keywords: Biosorption, heavy metals, pollutants, stormwater management systems.

 
Simulation of subtropical marine stratocumulus clouds in convection-resolving models
Authors: Heim Christoph , Hentgen Laureline , Ban Nikolina , Schär Christoph
Published: March 2020

Even though the complexity and resolution of global climate models (GCMs) has increased over the last decades, the inter-model spread of equilibrium climate sensitivity has not narrowed. The representation of subtropical low-level clouds and their associated radiative feedbacks in climate models still poses a major challenge. A fundamental problem underlying the simulation of such clouds is their multiscale nature. On the one hand, current GCMs allow to capture the large-scale processes but are too coarse to represent the mesoscale and microscale dynamical processes governing their formation and dissipation. On the other hand, large eddy simulations (LES) resolving the micro scale are bound to small domains and thus lack a robust representation of the large-scale flow and the mesoscale organisation of the clouds. Convection-resolving models (CRMs) are an attractive compromise between the former two since they allow for simulations at much higher resolution than in conventional GCMs and on larger domains than in LES.

Here we analyse how CRMs simulate stratocumulus decks and investigate causes for inter-model differences. We consider a set of ten CRMs (nine GCMs that are run at convection-resolving resolution during a short time period as part of the pioneering DYAMOND initiative, and the limited area model COSMO run by ourselves) used to simulate stratocumulus clouds over the South-East Atlantic during a 40 day period. The simulations cover a range of horizontal grid spacings between 5 and 1 km.

We find pronounced differences in the mean cloud cover among the analysed CRMs. In comparison to observed radiation (CERES), most of them underestimate cloud cover, in particular the low-lying stratus decks close to the African coast. Nevertheless, the simulated mesoscale cloud organisation is realistic and similar in the set of CRMs, with few exceptions showing organisation on larger scales than in the other models. In general, the simulated cloud field appears to be more sensitive to the model choice than to the horizontal resolution.

Despite the differences in the cloud cover, most models capture the subtropical inversion and its spatial structure relatively well. Therefore, differences in the inversion strengths do not suffice to explain variability in the simulated cloud cover fraction between models. However, we find a relation between the mean height of the stratocumulus layer (or inversion layer) and its cloud cover fraction: Models with higher inversions tend to simulate a higher cloud cover fraction, bringing them closer to observations. Similarly, stronger vertical mixing within the boundary layer and enhanced surface latent heat fluxes appear to be related to higher cloud cover. Such relations may help to determine the physical processes responsible for the differences among CRMs in the simulated stratocumulus field.
Precipitation diurnal cycle and associated valley wind circulations over an Andean glacier region (Antizana, Ecuador)
Authors: Junquas Clementine , Heredia Maria Belen , Condom Thomas , Espinoza Jhan Carlo , Ruiz Jean Carlos , Rabatel Antoine
Published: March 2020

In the tropical Andes, the evolution of the mass balance of glaciers is strongly controlled by the variability of precipitation and humidity transport. It is therefore crucial to better understand the main patterns of precipitation in terms of spatio-temporal distribution at the local scale. In this study, we focus on the region of the Antizana ice cap, located in the Equatorial Andes about 50 km east of the city of Quito (Ecuador). In addition, the Antizana region is located in a very complex zonal climate gradient, with the Pacific Ocean to the west and the humid Amazonian plains to the east, including an area of ​​maximum precipitation on the Amazonian slope, also called "Precipitation hotspot".

In this study, we perform dynamical downscaling using a Regional Climate Model (RCM) to improve the understanding of the atmospheric processes controlling the spatio-temporal variability of precipitation. The WRF (Weather Research and Forecasting) model is used to perform a set of ten experiments with four one-way nesting domains (27km, 9km, 3km, 1km), with the highest resolution domain centered on the Antizana mountain, for the year 2005. For the model validation, we use the 3B42 satellite product of the Tropical Rainfall Measuring Mission (TRMM) at 3-hourly time step, the ORE Antizana meteorological station (SNO GLACIOCLIM, LMI GREATICE) at hourly time step, and 2 meteorological in-situ stations, installed by the Instituto Nacional de Metereología e Hidrologia (INAMHI) in the Antizana region, with a complete chronology of daily precipitation (mm/day) during the 2005 year.

We test different forcings of DEM (Digital Elevation Model), microphysic schemes, Cumulus schemes and convection-permitting simulation, and radiation/slope dependent options. The analysis focuses in particular on how the different representation of thermally driven valley wind circulation can affect the diurnal cycle of precipitation at the ORE Antizana in-situ station. The influence of the diurnal cycle of the regional humidity flux on the mountain precipitation is also analyzed.
Uncertainty Analysis of Sub-daily Precipitation Extremes estimated from Satellite Datasets on a Global Scale
Authors: Hu Lanxin
Published: March 2020

Precipitation extremes and associated hazards pose a significant risk to society and the economy on a global scale. Effective mitigation strategies require accurate estimates of the intensity and frequency of those extremes. Traditional approaches for precipitation frequency analysis rely on long-record from in-situ observations, which however are not available on a global scale. Satellite and reanalysis-based products provide global precipitation estimates suitable for frequency analysis due to their extensive spatial coverage. However, errors in global precipitation products lead to significant bias in the quantification of extremes and potential changes. To examine this issue, five regions(Austria, north Italy, Florida, Texas, Arizona) that include a high-density gauge network (>3 gauges/satellite pixel) are selected as references to evaluate the uncertainty in retrieving extreme value statistics based on four global precipitation products (MSWEP, IMERG, GSMaP, CMORPH). The statistical properties of extremes are based on the application of the Metastatistical Extreme Value (MEV) framework. MEV has been validated in previous studies that have demonstrated that the method is able to provide robust estimates of high quantiles from short data records. In this work we evaluate the uncertainty on the estimation of extremes focusing primarily on the dependence to a) data characteristics and b) hydroclimatic region. Additionally, we evaluate the sub-grid variability of extreme precipitation and we demonstrate the impact of spatial scale mismatch (i.e. point vs satellite pixel) on the frequency analysis of extremes. This work provides a relatively comprehensive assessment of the use of MEV for estimating precipitation extremes from globally available datasets and an understanding of the variability of sub-daily precipitation extremes at different hydroclimatic regions of the world.
Determining P- and S-wave velocities and Q-values from single ultrasound transmission measurements performed on cylindrical rock samples: it’s possible, when…
Authors: Boxberg Marc S. , Duda Mandy , Löer Katrin , Friederich Wolfgang , Renner Jörg
Published: March 2020

Determining elastic wave velocities and intrinsic attenuation of cylindrical rock samples by transmission of ultrasound signals appears to be a simple experimental task, which is performed routinely in a range of geoscientific and engineering applications requiring characterization of rocks in field and laboratory. P- and S-wave velocities are generally determined from first arrivals of signals excited by specifically designed transducers. A couple of methods exist for determining the intrinsic attenuation, most of them relying either on a comparison between the sample under investigation and a standard material or on investigating the same material for various geometries.

Of the three properties of interest, P-wave velocity is certainly the least challenging one to determine, but dispersion phenomena lead to complications with the consistent identification of frequency-dependent first breaks. The determination of S-wave velocities is even more hampered by converted waves interfering with the S-wave arrival. Attenuation estimates are generally subject to higher uncertainties than velocity measurements due to the high sensitivity of amplitudes to experimental procedures. The achievable accuracy of determining S-wave velocity and intrinsic attenuation using standard procedures thus appears to be limited.

We pursue the determination of velocity and attenuation of rock samples based on full waveform modeling and inversion. Assuming the rock sample to be homogeneous - an assumption also underlying standard analyses - we quantify P-wave velocity, S-wave velocity and intrinsic P- and S-wave attenuation from matching a single ultrasound trace with a synthetic one numerically modelled using the spectral finite-element software packages SPECFEM2D and SPECFEM3D. We find that enough information on both velocities is contained in the recognizable reflected and converted phases even when nominal P-wave sensors are used. Attenuation characteristics are also inherently contained in the relative amplitudes of these phases due to their different travel paths. We present recommendations for and results from laboratory measurements on cylindrical samples of aluminum and rocks with different geometries that we also compare with various standard analysis methods. The effort put into processing for our approach is particularly justified when accurate values and/or small variations, for example in response to changing P-T-conditions, are of interest or when the amount of sample material is limited.
Neogene-to-Quaternary post-orogenic tectonic evolution and CaCO3-rich fluids from the Tabernas basin (eastern Betics, Spain) reveal control by deep-seated processes in the mantle
Authors: Larrey Marine , Mouthereau Frédéric , Masini Emmanuel , Calassou Sylvain , Virgone Aurélien , Gaucher Eric , Huyghe Damien , Beaudoin Nicolas
Published: March 2020

Since Miocene times, the crustal thinning in eastern Betics and the Alboran region associated with westward slab retreat led to the formation and exhumation of metamorphic domes and EW-directed narrow basins.

The Tabernas basin preserves a sedimentary records of the last stages of metamorphic domes exhumation (14 to 8 Ma). Structural constraints from fault patterns and sedimentary archives show evidence in the field for E-W strike-slip faults that developed close to dome-basin contacts. The evolution of strike-slip faulting and extensional basins reveals strain partitioning during the late Miocene that is consistent with the present-day regional NNW-directed compression and WSW-directed/orogen-parallel extension that result from the NW-SE Africa-Europe plate convergence. A regional cross-section further emphasizes the role of crustal-scale strike-slip faulting and slab detachment and delamination under the Alboran domain.

Calcite veins that developed during the orogen-parallel extension in the metamorphic basement and the Tortonian sedimentary rocks show a wide variety of stable isotopes ratios. Calcite cements have δ18O values ranging from -17.23‰ to -5.30‰ for, and from -15.77‰ to -1.6‰ for δ13C isotopic ratios. This patterns is interpreted to reflect the increase of freshwater input buffered by the composition of host carbonate rocks.

Continental carbonates of Quaternary ages are widespread in the Tabernas basin. Travertines show a close structural relationship with N170 and N50 normal faults, implying tectonically-controlled Ca/CO2 leakages. Their δ13C values are compatible with a hydrothermal origin from a deep-seated carbon source (δ18O median of -7.5‰, δ13C median of 2.1‰). Degassing associated with regional volcanism from the Serravallian until the Tortonian-Messinian ages is likely to be also the main vector of recent CO2 storages in rocks. The U-Th ages of travertines, ranging from 8ka ± 0.2 to 354ka ±76, further outline interactions with captive aquifer from 350ka and subsequent Ca/CO2 leakages due to geodynamic changes.
The Basque-Cantabrian Basin: a natural laboratory to study the reactivation of a hyperextended system
Authors: Miro Padrisa Jordi , Cadenas Patricia , Lescoutre Rodolphe , Muñoz Josep Anton , Manatschal Gianreto
Published: March 2020

The Basque – Cantabrian Basin (BCB) corresponds to a Mesozoic hyperextended rift basin that was subsequently reactivated from Late Cretaceous to Cenozoic and is at present part of the Pyrenean orogen. Numerous studies have addressed the role of rift inheritance on the formation of orogens, but little consideration has been given to the rift segmentation and the along strike variability. In the BCB, most studies focused on a section at the central part of the basin, despite the amount of geological and geophysical data available on the entire area, which make it a perfect natural laboratory to study the reactivation of a hyperextended basin.

The aim of this study is threefold: (I) reveal the 3D geometry and the along strike variability of the BCB by doing three N-S transversal cross sections from east to west; (II) define the rift domains and their limits; and (III) study the impact of rift inheritance during the compressional reactivation mainly focusing on the former distal rift domains.

Our preliminary results show that the BCB is affected by a multistage and polyphase rift evolution including a first, widespread Permo – Triassic rift phase including Late Triassic salt, a Late Jurassic to Barremian extensional phase and a more prominent Aptian to Middle Cenomanian hyperextension phase.  This complex rift template had a major impact on the subsequent reactivation and can explain some of the along strike variabilities observed within the three regional cross sections. To the east, the BCB was completely reactivated and transported to the south over the Late Triassic salt, which acted as a decoupling level. On the contrary, the westernmost section preserves the rift-related structures only weakly reactivated, providing direct insights on the early stages of reactivation. Our observations show that underthrusting/subduction initiates within the exhumed mantle domain, while during initial collision, the necking domains acted as a buttress. Decollement levels during early stages are located in the former rift distal domains and use serpentinized mantle rocks, while during collision they migrate to more external parts and use intra-basement decoupling levels such as the ductile middle crust and/or salt horizons.

Key words: Rift inheritance, Pyrenees, Basque – Cantabrian Basin, hyperextension.
Using deep learning to transfer knowledge between satellite datasets for automated agricultural land discrimination in Afghanistan
Authors: Hamer Alex , Simms Daniel , Waine Toby
Published: March 2020

Accurate mapping of agricultural area is essential for Afghanistan’s annual opium poppy monitoring programme. Access to labelled data remains the main barrier for utilising deep learning from satellite imagery to automate the process of land cover classification. In this study, we aim to transfer knowledge from historical labelled data of agricultural land, from work on poppy cultivation estimates undertaken between 2007 and 2010, to classify imagery from a range of sensors using deep learning. Fully Convolutional Networks (FCNs) have been used to learn the complex features of agriculture in southern Afghanistan using their inherent spatial and spectral characteristics from satellite imagery. FCNs are trained and validated using labelled Disaster Monitoring Constellation (DMC) data (32 m) to transfer knowledge of agricultural land to classify other imagery, such as Landsat (30 m). The dependency on spatial and spectral characteristics are explored using intensity, Normalised Difference Vegetation Index (NDVI), top of atmosphere reflectance and tasselled cap transformation. The underlying spatial features associated with agriculture are found to play a significant role in agriculture discrimination. High classification performance has been achieved with over 92% overall accuracy and 0.58 intersection over union. The ability to transfer knowledge from historical datasets to new satellite sensors is an exciting prospect for future automated agricultural land discrimination in the United Nations Office on Drugs and Crime annual opium survey.
Anthropogenically-induced recharge in a semiarid mountain front context
Authors: Bouimouass Houssne , Fakir Younes , Tweed Sarah , Leblanc Marc
Published: March 2020

Mountain-fronts constitute important groundwater recharge areas in arid and semiarid regions. Mountain-front recharge processes are generally identified, in natural systems, as streamflow losses and subsurface inflow from the mountain block. However, another key recharge process is from irrigation practices; where mountain streamflow is distributed across the irrigated piedmont. In this study, coupled groundwater fluctuation measurements and stable isotopes (18O and 2H) were used to identify and compare the natural mountain-front recharge to the anthropogenically-induced irrigation recharge. Within the High-Atlas mountain front of the Ourika basin, Tensift, Central Morocco, the groundwater fluctuation mapping from the dry to wet season showed that recharge from irrigation waters was higher than the recharge along the streambed. Irrigation practices in the region divert more than 65% of the stream water, thereby reducing the potential for stream recharge. Due to the traditional irrigation practices, upstream crops are preferentially irrigated with stream water over downstream areas. In downstream areas irrigation is only via stream water during large flood events and is otherwise supplemented by groundwater resources. These changes in water resources used for irrigation practices between upstream and downstream areas are reflected in the spatio-temporal evolution of the stable isotopes of groundwater. In the upstream irrigation area, the groundwater stable isotope values (d18O: -8.4 ‰ to -7.4 ‰) reflect recharge by the diverted stream water. In the downstream irrigation area, the groundwater isotope values are lower (d18O: -8.1 ‰ to -8.4 ‰) due to recharge with floods.

The results from this study particularly highlight that irrigation can deeply modify both the recharge processes and the water balance in the mountain front areas. Groundwater resources in such areas become reliant on the irrigation practices as an important source of recharge, and this anthropogenic modification of the hydrological cycle should be assessed and taken into consideration within climate change impacts and integrated water management strategies.
Modelling large-scale fractured reservoirs efficiently for geothermal energy and groundwater flow
Authors: Oldfield Simon , Lüthje Mikael , Welch Michael , Smit Florian
Published: March 2020

Large scale modelling of fractured reservoirs is a persistent problem in representing fluid flow in the subsurface. Considering a geothermal energy prospect beneath the Drenthe Aa area, we demonstrate application of a recently developed approach to efficiently predict fracture network geometry across an area of several square kilometres.

Using a strain based method to mechanically model fracture nucleation and propagation, we generate a discretely modelled fracture network consisting of individual failure planes, opening parallel and perpendicular to the orientation of maximum and minimum strain. Fracture orientation, length and interactions vary following expected trends, forming a connected fracture network featuring population statistics and size distributions comparable to outcrop examples.

Modelled fracture networks appear visually similar to natural fracture networks with spatial variation in fracture clustering and the dominance of major and minor fracture trends.

Using a network topology approach, we demonstrate that the predicted fracture network shares greater geometric similarity with natural networks. Considering fluid flow through the model, we demonstrate that hydraulic conductivity and flow anisotropy are strongly dependent on the geometric connection of fracture sets.

Modelling fracture evolution mechanically allows improved representation of geometric aspects of fracture networks to which fluid flow is particularly sensitive. This method enables rapid generation of discretely modelled fractures over large areas and extraction of suitable summary statistics for reservoir simulation. Visual similarity of the output models improves our ability to compare between our model and natural analogues to consider model validation.
Ice supersaturated regions: properties and validation of ERA-Interim reanalysis with IAGOS in situ water vapor measurements
Authors: Reutter Philipp , Neis Patrick , Rohs Susanne , Sauvage Bastien , Spichtinger Peter , Petzold Andreas
Published: March 2020

Cirrus clouds and their potential formation regions, so-called ice-supersaturated regions (ISSRs) occur frequently in the tropopause region. It is assumed that ISSRs and cirrus clouds can change the tropopause structure by diabatic processes, driven by latent heating due to phase transitions and interaction with radiation. These effects may also alter the distribution of potential vorticity (PV) in the upper troposphere, thus leading to changes in large scale dynamics and stratosphere-to-troposphere exchange.  

The measurement of water vapour at the tropopause level is not trivial. Beside radiosonde data the most important in-situ dataset is provided by in-service passenger airplanes. The European Research Infrastructure ’In-service Aircraft for a Global Observing System’ (IAGOS) (Petzold et al., 2015) provides long-term in-situ measurements on board commercial passenger aircraft. Along its flight track every aircraft is monitoring the chemical composition of the surrounding air and atmospheric state parameters by compact instruments. Especially in the upper troposphere/lowermost stratosphere (UTLS) these measurements are very valuable as most flight tracks are situated in heights between 9 to 13 km, depending on the actual weather conditions, seasons and geographic region. 

However, for many research questions a three-dimensional picture including a sufficient temporal resolution of the water vapour fields in the UTLS region is required. Hence, in our study we use the in-situ data from IAGOS to quantify the quality of the established and often used ERA-Interim data set. The underlying IFS-model of this reanalysis data allows explicitly ice-supersaturation in cloud free conditions and is therefore suitable for comparison. For instance, we compare properties such as the seasonal cycle of the vertical distribution of water vapour mixing ratio, relative humidity and the fraction of ice-supersaturated regions. 
An Analysis of Regional H2O and CH3OH Production rates of Comet 67P from the MIRO Measurements
Authors: Lai Hsuan-Ting , Ip Wing-Huen , Tseng Wei-Ling , Lai Ian-Lin , Marshall David
Published: March 2020

The coma structure and gas production rates of H2O, CO, CH3OH, and NH3 of comet 67P/Churyumov-Gerasimenko were investigated in detail by different instruments onboard the Rosetta spacecraft between August 2014 and September 2016. We analyzed the nadir-pointing microwave spectroscopic data from the MIRO experiment before and during the perihelion passage in June, July, and August 2015 in order to examine the solar zenith angle dependence of the gas production rates (Q) of H2O and CH3OH, respectively. From a detailed analysis of the spectral shapes of H218O at a frequency of 547.676 GHz and those of CH3OH at 553.146 GHz, the surface distributions of H2O and CH3OH can be mapped. We found that the Q-values generally increased with solar insolation. However, there also existed large variations that might be related to chemical heterogeneity of the cometary nucleus surface (or subsurface in individual geomorphological areas and at different spatial scales). A comparison of the CH3OH/H2O mixing ratio in the two lobes will also be attempted.
Variation behavior of tidal dynamics in the Yangtze Estuary: implying the amplification of hydrodynamics and sediment dynamics by the human intervention
Authors: Cheng Heqin , Chen Wei , Teng Lizhi , Yuan Xiaoting
Published: March 2020

During the last decades, many estuarine systems in Europe (e.g. the Elbe, Ems, Loire) have shown increases in tidal range and in turbidity, which are linked to local human activity (i.e., deepening). Compared to these European estuaries, the Yangtze Estuary is much larger in scales, experiences much stronger river discharge, and it is subject to a strong seasonal variation in freshwater and sediment supply from the drainage area. Moreover, the Yangtze estuary is a complex network with several branches, connecting channels. The changes in the flow and sediment dynamics in the estuary may result from both local and nonlocal human activities. Despite the intense research efforts over the past two decades, it is still unclear which impact (local or nonlocal) is responsible for the changing flow and sediment characteristics in the estuary. Deep investigation of tidal characteristic quantities such as extreme tidal level, tidal range, amplitude of tidal constituents, tidal characteristic coefficient and suspended sediment concentration is performed in a systematic manner. It is accomplished using the extreme value analysis, the wavelet analysis and harmonic analysis of water level at 11 hydrography stations along the tidal river channel (Datong-Nanjing reach) and estuarine section (downstream the Xuliujing) during 2008-2016. Similar data analysis is also performed for the last four decades of 20th century and results are compared with the analysis of the recent measurements. The driving forces of the significant changes in tidal characteristic quantities and suspended sediment concentration are discussed. Results show that the tidal dynamics in the Yangtze estuary has been enhanced. Its seasonal variation is attributed to the adjustment of runoff distribution, which is mainly caused by the operation of Three Gorges Dam. In short-term, local changes of flow/sediment dynamics, terrain changes play a major role. In the long term (on the 40-year time scale), the effect of sea level rise on the increasing M2 constituent is obvious. This has mainly resulted from the enhancing anti-clockwise rotation of the synchronous tidal phase.

 
The state of Kersten Glacier and the Northern Icefield on Mt. Kilimanjaro
Authors: Stadelmann Catrin , Fürst Johannes , Seehaus Thorsten , Mölg Thomas , Braun Matthias
Published: March 2020

The glaciers on Kilimanjaro are unique indicators for climatic changes in the tropical mid-troposphere of Africa. Glaciers in the tropics have shown a severe retreat since the Last Glacial Maximum and the glaciers on Mt. Kilimanjaro are no exception, with an 85% reduction in glacier area from 1912 to 2013. This history of severe glacier area loss raises concerns about an imminent future disappearance. Yet, the remaining ice volume is not well known.

By combining state-of-the-art techniques from satellite remote sensing and glacier mass balance modelling with data assimilation, we inferred the  glacier ice thickness of two selected glaciers on Mt. Kilimanjaro. We reconstruct thickness maps for 2000 and 2011 for the Northern Icefield and Kersten Glacier and find mean thickness values of 26.6 and 9.3 m for 2011, respectively. Model validation was difficult for Kersten Glacier, as no ice thickness  measurements were available. Thus, the first attempt to use decadal retreat information, to infer past glacier ice thickness, which are used to do a glacier-specific calibration of the ice thickness reconstruction, was conducted by creating a generic margin thickness from glacier outlines and DEM differencing. This approach proved to be reasonable for Kersten Glacier, where a more common glacier type was assumed, but seemed to underestimate ice thickness at the Northern Icefield, because of the complex topography.

The poster summarizes the results obtained from the thickness reconstructions and compares them to thickness maps from an existing global consensus estimate. In comparison to our results the consensus estimate shows unrealistically thick values for KG in areas that are meanwhile ice-free. A rough projection on glacier recession based on the generated thickness data agrees with other estimates pointing towards the disappearance of the glaciers between 2040 and 2060.
Synthetic seismograms for assessing areas of potential damage after induced events for legal regulations in Germany
Authors: Gestermann Nicolai , Plenefisch Thomas
Published: March 2020

Induced and triggered seismicity in Germany is related to various mining operations such as hydrocarbon extraction, geothermal exploitation and classical mining techniques, i.e. coal and potash mining.

After some larger events small damages to buildings were observed that might have been caused by the ground shakings. This led to public discussions on compensation and to political discussions on improving legal regulations. The possibility of damages caused by mining induced seismic events and difficulties in financial compensation reduced the acceptance of mining projects in the past, e.g. geothermal projects are inhibited.

In case of verified damage due to an induced event, the causative mining company has to pay compensations. In 2016 new legal regulations entered into force. The Federal Mining Act was revised with an improved legal situation for the population by expanding the prima facie evidence on mining activities using boreholes. The new legal regulations define, that damages at buildings are assumed to be caused by the seismic event in the responsibility of the operator of the mining activities, if they occur within a certain area defined by the mining authority (impact area, German: “Einwirkungsbereich”).

From the seismological perspective, local measurements of PGV are often rare. Thus, it is difficult to assess the damage potential of the seismic events in detail, especially if intensities are around V (EMS-98). In many cases, a relation between individual damages at buildings and the seismic event is only hardly verifiable. Actually, detailed survey reports could neither prove nor disprove the relation between damages and seismic events in some cases. In conclusion, some of the widely discussed events might have led to small damages.

A brief introduction about the existing legal regulations will be presented. We used synthetic seismogram to model the wave propagation and amplitude effects for induced seismic events in the magnitude range between ML 2.9 and 3.6, for which it was necessary to define the impact area for legal regulations. Results from amplitude measurements at existing seismic stations were taken to calibrate the absolute amplitudes of the modeling. The synthetic seismograms could help to quantify the effects from the radiation pattern of the source and the impact of sediment coverage between source and receivers. They could improve the definition of the area of impact.
HMCtomo: A framework for Hamiltonian Monte Carlo sampling of Bayesian geophysical inverse problems
Authors: Gebraad Lars , Zunino Andrea , Fichtner Andreas , Mosegaard Klaus
Published: March 2020

We present a framework to solve geophysical inverse problems using the Hamiltonian Monte Carlo (HMC) method, with a focus on Bayesian tomography. Recent work in the geophysical community has shown the potential for gradient-based Monte Carlo sampling for a wide range of inverse problems across several fields.

 

Many high-dimensional (non-linear) problems in geophysics have readily accessible gradient information which is unused in classical probabilistic inversions. Using HMC is a way to help improve traditional Monte Carlo sampling while increasing the scalability of inference problems, allowing access to uncertainty quantification for problems with many free parameters (>10'000). The result of HMC sampling is a collection of models representing the posterior probability density function, from which not only "best" models can be inferred, but also uncertainties and potentially different plausible scenarios, all compatible with the observed data. However, the amount of tuning parameters required by HMC, as well as the complexity of existing statistical modeling software, has limited the geophysical community in widely adopting a specific tool for performing efficient large-scale Bayesian inference.

 

This work attempts to make a step towards filling that gap by providing an HMC sampler tailored for geophysical inverse problems (by e.g. supplying relevant priors and visualizations) combined with a set of different forward models, ranging from elastic and acoustic wave propagation to magnetic anomaly modeling, traveltimes, etc.. The framework is coded in the didactic but performant languages Julia and Python, with the possibility for the user to combine their own forward models, which are linked to the sampler routines by proper interfaces. In this way, we hope to illustrate the usefulness and potential of HMC in Bayesian inference. Tutorials featuring an array of physical experiments are written with the aim of both showcasing Bayesian inference and successful HMC usage. It additionally includes examples on how to speed up HMC e.g. with automated tuning techniques and GPU computations.
Pre-eruptive magmatic processes and their timescales revealed by crystal zoning
Authors: Albert Helena , Sainz-Maza Sergio , Geyer Adelina , López Carmen
Published: March 2020

Understanding the processes that occur in the magma plumbing systems prior to eruption and how they relate to monitoring data can lead to improved volcanic hazard assessment. Crystal compositions are witnesses of the architecture and dynamics of the plumbing system, and crystal zoning patterns can inform us of the range of magmatic environments, and of the likely processes that lead to eruption. We have studied the petrology and the geochemistry of the monogenetic historical eruptions occurred in Tenerife (Canary Islands) that come out through the rift zones (NW and NE Rifts) as well as the last mafic intra-caldera monogenetic eruption of Montaña Mostaza (15 ka). The deposits from the NE Rift and the intra-caldera contain complexly zoned olivine crystals suggesting open system and magma mixing, while crystals from the NW Rift are mainly normally zoned. By modelling the zonation patterns of the crystals we have calculated the timescales of the magma intrusions and ascent to the surface. We have found that the magmas erupted along the NW rift are more evolved and vary from basanites to phono-tephrites, while the magmas from the NE rift are basanites recording different mixing events between magma pockets occurred around 1-2 years, 3 months and few days before the eruption. The olivine crystals from the intra-caldera eruption display more variety in the zoning patterns than the eruptions from the rift, suggesting a more complex history. Based on the integration of the petrological and modelling results with gravimetric and geophysical data we propose, at least, three main different ascent histories (paths and timescales) for monogenetic eruptions in Tenerife.

This research has been partially funded by the EUROVOLC project (Horizon 2020 Grant Agreement: 731070).