bluuebunny/crossref_metadata_2025 huggingface dataset:
An assessment of Random Forest wrappers for selecting important features of spectroscopy data in the modelling of soil properties
Authors: Canero Francisco M. , Cardenas-Martinez Aaron , Aragones David , Rodriguez-Galiano Victor
Published: March 2022

Soil properties could be assessed with reflectance spectroscopy (soil spectroscopy, SS) in vis-NIR region (400-2500 nm) through absorption features found in soil spectra. A high spectral resolution (up to 1 nm) drives to high dimensional and multicollinear data. This issue is usually addressed prior to modelling with feature extraction methods such as Principal Component Analysis, or embedded methods such as Partial Least Squares Regression (PLSR). Feature Selection (FS) wrapper methods are promising dimensionality reduction approaches barely used in SS. The objective of this study was two-fold: i) evaluate the performance of FS wrapper methods built from Random Forest (RF) algorithm to predict soil organic matter (SOM), clay and carbonates using laboratory spectroscopy, ii) test the performance of FS methods for dimensionality reduction in SS. The reflectance of 100 soil samples from Sierra de las Nieves National Park (Spain), was measured under laboratory conditions using an ASD FieldSpec Pro JR. A spectral preprocessing method, Continumm Removal (CR), was applied to raw spectra. The RF wrapper considered two different feature searching approaches: Sequential Forward Selection (SFS) and Sequential Flotant Forward Selection (SFFS). The performance of RF with FS (RF-FS) was compared to that of Partial Least Squares Regression (PLSR) and RF (without FS). Models were evaluated with R-squared, root mean squared error (RMSE) and ratio of prediction to deviation (RPD).

RF-FS models outperformed PLSR and RF models for the three SAP. RF-FS best models had a RPD of 2.19 for SOM, 1.64 for carbonates and 1.52 for clay, whereas PLSR models had RPD values of 1.59, 1.22 and 1.3, and RF 1.38, 1.23 and 1.23 for SOM, carbonates, and clay, respectively. Therefore, FS was useful in obtaining models with improved accuracy by reducing redundant features and avoiding multicollinearity (Hughes effect). The application of FS wrapper methods reduced the number of features in the RF-FS models to less than 1% of the starting features. Features were selected across all spectra from SOM and clay, and around 900, 1900 and 2350 nm for carbonates. This research, thus, shows an alternative to different feature extraction approaches for modelling soil properties based on FS methods and machine learning.
Rossby wave teleconnections to rainfall anomalies over Vietnam
Authors: Le Hong-Hanh , Hall Nicholas , Ngo-Duc Thanh
Published: March 2022

Remote influences on extreme anomalous rainfall over North and South Vietnam during extended summer (May-October) are explored using a 38-year (1979-2016) ERAi global dataset. Composite WET and DRY events with lags of up to two weeks are assembled for rainfall indices over subregions of Vietnam. The large-scale dynamical precursors to these events are explored through diagnostics of the extratropical flow. 

Rainfall extremes of opposing signs show asymmetrical large scale precursors and different pathways of influence. Both WET and DRY events over North Vietnam are seen to originate from Europe and propagate either at high latitudes or along the Asian Jet. A persistent Siberian High is linked with WET events over North Vietnam. Anomalies also develop along the Asian Jet for both regions, but only for DRY events over South Vietnam. Events over South Vietnam are also much more influenced by tropical precursors. 

The Dynamical Research Empirical Atmospheric Model (DREAM) was used to examine pathways of influence to the circulation over Vietnam sub-regions in the medium range. A set of stationary wave experiments was conducted with artificial heat sources in different locations around the world, using ERAi summer climatology as a basic state. Influence functions with respect to upper-level divergent flow over the target regions of North and South Vietnam indicate two different pathways: extratropical wave-trains and tropical waves. For North Vietnam, heat sources over Europe give the most influence after 15 days. For South Vietnam, the influence is much weaker and significant precursors are more likely to be tropical Kelvin wave sources. 
Dilatation and shearing in tectono-volcanic systems from poro-elasto-plastic models set in the Southern Andes Volcanic Zone context, inferences on geofluid flow
Authors: gerbault muriel , Saez Felipe , Ruz Ginouves Javiera , Cembrano José , Iturrieta Pablo , Hurtado Daniel , Hassani Riad , Browning John
Published: March 2022

Geothermal fields near volcanic complexes and active crustal-scale fault zones require an understanding of the mechanical interactions that control variations in pore fluid pressure at a crustal scale. Crustal faults can trigger and modify fluid flow depending mostly on their geometry and mechanical properties. In turn, fluid flow reduces normal stresses causing either shearing or dilation through the rock mass, concomitant with hydraulic fracturing or seismic fault reactivation. The Southern Andes Volcanic Zone (SAVZ) documents widespread geofluid migration through the crust within a bulk regional transpressive regime. We address here the key role of dilatational domains potentially hosting geothermal fluids, in close relation to shear zones, by using elasto-plastic and poro-elasto-plastic models.

First we define models considering Drucker-Prager elasto-plasticity, that account for either: 1) an inflating magmatic cavity or 2) a dextral slipping fault zone ca. 4 km apart, to assess the rheological conditions leading to brittle failure of the bedrock around the fault zone and the cavity, respectively. This setup is applied to the San-Pedro Tatara volcanic complex in the SAVZ. Parametric tests of Young’s moduli and frictional strength provide not only the conditions for macro-scale shear failure, but also shows the development of diffuse domains of dilatational strain in the intervening bedrock. Both void opening and/or volumetric cracking may lead to an increase in porosity and/or permeability, allowing over-pressurized geofluids to migrate within these domains. Our results (Ruz Ginouves et al., JVGR, 2021) show that generally, shallow magma chambers (~< 4 km) and fault zones must be close enough to trigger bedrock failure of the other counterpart (< 4 km), unless the magma chamber is deeper than 10 km, the magma overpressure is high or the regional strength is very low. We argue that alternating strike-slip faulting and magmatic overpressure promote a variety of stress fields that may explain observations of transient fluid pathways on seemingly independent timescales along the Andean margin.

To gain further insights into these processes, we develop a numerical scheme to quantify stress and fluid flow with a coupled poro-mechanical approach implemented using Python’s Opensource FEM library FeniCS. Benchmarks are first presented to validate our poro-elasto-plastic approach. Then a synthetic setup shows how fluids get channelized around a fault zone several days after an imposed fault slip motion. Preliminary results are discussed in comparison to a high enthalpy geothermal system associated with another volcanic complex in the SAVZ.
Model predictions of overwash extent into the marginal ice zone. 
Authors: Pitt Jordan , Bennetts Luke
Published: March 2022

Overwash is an important aspect of the dynamics in the marginal ice zone where sea ice and ocean waves interact. Overwash dissipates wave energy, and the presence of water on top of sea ice can drive growth or melting, depending on the local thermodynamic conditions. The presence of water on floes is also important for biologic and chemical processes. While overwash has been observed and investigated under experimental conditions, it has not yet been studied in the marginal ice zone. One reason for this lack of in-situ measurements and observations is due to the marginal ice zone being highly dynamic, and the onset of overwash only occurring under specific and sensitive conditions. To facilitate future observations we have produced a model of the extent of overwash into fields of sea ice by combining a new model of the onset of overwash and a standard attenuation model. This model of overwash extent is validated against experimental observations and is used to provide the extent of overwash for realistic ice and wave field conditions observed during the July 2017 voyage of the South African icebreaker S.A. Agulhas II. 

 
Time-dependent earthquake and tsunami hazard scenarios for the Adriatic region
Authors: Peresan Antonella , Hassan Hany M.
Published: March 2022

During the last two decades, an operational procedure for time-dependent seismic hazard scenarios has been developed, which integrates fully formalized and validated earthquake forecasting information from pattern recognition analysis (e.g. by CN algorithm), with the realistic modelling of earthquake ground motion by the neo-deterministic approach (NDSHA). The proposed methodology permits to define, both at regional and local scale, a set of scenarios of ground motion for the time interval for the time interval in which a strong event is likely to occur within the alerted areas. When dealing with offshore large earthquakes occurrence, this integrated approach can be naturally extended to the definition of time-dependent tsunami scenarios, based on physical scenario models of tsunami waves.

CN forecasts for the Italian territory and its surroundings, as well as the corresponding time-dependent ground motion scenarios associated with the alarmed areas, are regularly updated since about two decades (Peresan, 2018, Geophysical Monograph Series, 234, pp. 149–172 and references therein). We review the results obtained so far by rigorous prospective testing of the developed procedure, including analysis of the statistical significance of issued forecasts. Special emphasis is placed on the recent earthquakes that occurred in the Adriatic region, which support validation of the applied methodologies, and evidence the opportunity of developing time-dependent tsunamis scenarios, by integrating forecast information with the modelling of tsunami waves propagation.

In this study, tsunami modelling is performed by the NAMI DANCE software (Yalciner et al., 2006, Middle East Technical University, Ankara, Turkey), which allows us accounting for seismic source properties, variable bathymetry, and non-linear effects in waves propagation. Urban scale hazard scenarios for selected coastal sites are developed considering different potential tsunamigenic sources of tectonic origin, located in the Central and Southern Adriatic Sea. The results from parametric studies accounting for possible sources related to historical events, as well as for yet unobserved extreme events, are considered for this purpose. Their verification against recent earthquakes, allows us assessing the relevance of space-time information and uncertainties on source parameters, and their possible operational contribution towards effective tsunami warning system for the Adriatic Sea and in the whole Mediterranean area. 
The role of intense rainfall events on the land degradation processes in the Slovak and Polish catchments  
Authors: Sabová Zuzana , Tomaščík Matúš , Németová Zuzana , Kohnová Silvia , Krajewski Adam , Banasik Kazimierz
Published: March 2022

Land degradation caused by anthropogenic activities (deforestation, overgrazing, unsuitable land-use and management practices) negatively influence the well-being of people and also accelerates soil erosion processes. The main evidence for a link between soil degradation and water erosion can be seen in the following elements: increasing rainfall intensity, permafrost thawing, biomass production, tillage, cultivation overgrazing, deforestation/ vegetation clearing, vegetation burning, poorly designed roads and paths to a global extent. Therefore, it is significant to investigate degradation processes in order to point out the possible adverse effects of unsuitable management practices of the landscape in the scale of past and future periods. A future prediction of the development of any processes requires long-term investigation and analysis of the phenomenon predetermined to assess future behaviour. On the contrary, analysis of past processes shows us precipitation patterns and reveals their effect on the generation of degradation processes. The study describes the role of rainfall events on a generation of erosion processes, especially soil water erosion in the catchments located in Poland (Zagożdżonka) and Slovakia (Svacenicky Jarok). A common characteristic of these catchments is the susceptibility to degradation processes, the predominance of arable land and the dominant agricultural use of catchments. In the case of Zagożdżonka catchment (Poland) the modelling period covers the years 1963-2020 with the real measured rainfall events. On the contrary, in the case of Svacenický jarok the future development of degradation processes was analyzed based on the future prediction of rainfall events covering the period 2020-2100 and generated by CLM model (Climate Land Model). In both cases, the simulations were performed using the physically-based EROSION-3D model and three scenarios were created in order to model different land cover, land use, soil types and crops on agricultural land. The first scenario reflects current catchment conditions, the second reflects the best conditions (more forests, fewer pastures and unprotected land) and the third involves worst-case conditions (no protective measures or changes of inappropriate management practices). The results provide insight into the development of degradation processes, illustrate how changes in rainfall patterns affect soil degradation processes in the past and future and take into account different scenarios of management practices together with an analysis of the impact of rainfall events on these processes.
Gaussian mixture models for clustering and calibration of ensemble weather forecasts
Authors: Jouan Gabriel , Cuzol Anne , Monbet Valérie , Monnier Goulven
Published: March 2022

Nowadays, most weather forecasting centers produce ensemble forecasts.  Ensemble forecasts provide information about probability distribution of the weather variables. They give a more complete description of the atmosphere than a unique run of the meteorological model. However, they may suffer from bias and under/over dispersion errors that need to be corrected. These distribution errors may depend on weather regimes. In this paper, we propose various extensions of the Gaussian mixture model and its associated inference tools for ensemble data sets.  The proposed models are then used to identify clusters which correspond to different types of distribution errors. Finally, a standard calibration method known as Non homogeneous Gaussian Regression (NGR)  is applied cluster by cluster in order to correct ensemble forecast distributions. It is shown that the proposed methodology is effective, interpretable and easy to use.  The clustering algorithms are illustrated on simulated and real data. The calibration method is applied to real data of temperature and wind medium range forecast for 3 stations in France. 
Technosols derived from bauxite residue tailings for effective revegetation and rehabilitation
Authors: Courtney Ronan
Published: March 2022

Bauxite residue, the by-product produced in the alumina industry, is generated at an estimated global rate of approximately 150 million tonnes per annum. Currently, the reuse of bauxite residue is low (∼2%), and consequently the bulk is stored in land-based impoundments.

If not adequately managed, exposed residue may be prone to dusting, wind and water erosion and can contaminate surrounding areas. Establishing vegetation covers (rehabilitation) is viewed as an effective strategy for mitigating against pollution risk and approaches used can be broadly divided into capping with inert soil material or establishing vegetation in the tailings surface (revegetation). Revegetation provides a strategy where topsoil material is scarce and avoids the sourcing of large volumes from other sites.

While bauxite residue is typically alkaline (pH 10-12), saline and lacking in nutrients the implementation of effective rehabilitation strategies can promote favourable soil conditions for plant growth. Results also show establishment of soil microbial communities and soil faunal activity. These positive rehabilitation effects are maintained for several years and demonstrate that residue can be transformed to a soil-like medium capable of supporting ecosystem function.
Guidelines for studying diverse types of compound weather and climate events
Authors: Bevacqua Emanuele , De Michele Carlo , Manning Colin , Couasnon Anaïs , Ribeiro Andreia F. S. , Ramos Alexandre M. , Vignotto Edoardo , Bastos Ana , Blesić Suzana , Durante Fabrizio , Hillier John , Oliveira Sérgio C. , Pinto Joaquim G. , Ragno Elisa , Rivoire Pauline , Saunders Kate , van der Wiel Karin , Wu Wenyan , Zhang Tianyi , Zscheischler Jakob
Published: March 2022

Compound weather and climate events are combinations of climate drivers and/or hazards that contribute to societal or environmental risk. Studying compound events often requires a multidisciplinary approach combining domain knowledge of the underlying processes with, for example, statistical methods and climate model outputs. Recently, to aid the development of research on compound events, four compound event types were introduced, namely (a) preconditioned, (b) multivariate, (c) temporally compounding, and (d) spatially compounding events. However, guidelines on how to study these types of events are still lacking. Here, we consider four case studies, each associated with a specific event type and a research question, to illustrate how the key elements of compound events (e.g., analytical tools and relevant physical effects) can be identified. These case studies show that (a) impacts on crops from hot and dry summers can be exacerbated by preconditioning effects of dry and bright springs. (b) Assessing compound coastal flooding in Perth (Australia) requires considering the dynamics of a non-stationary multivariate process. For instance, future mean sea-level rise will lead to the emergence of concurrent coastal and fluvial extremes, enhancing compound flooding risk. (c) In Portugal, deep-landslides are often caused by temporal clusters of moderate precipitation events. Finally, (d) crop yield failures in France and Germany are strongly correlated, threatening European food security through spatially compounding effects. These analyses allow for identifying general recommendations for studying compound events. Overall, our insights can serve as a blueprint for compound event analysis across disciplines and sectors.
Snow water equivalents from snow depths: improvements of the DeltaSNOW model
Authors: Winkler Michael , Schellander Harald
Published: March 2022

Snow water equivalent (SWE) is probably the most important snowpack property, but due to various reasons it has been measured by far less frequently and continuously than, e.g., snow depth (HS). Recent modelling efforts led to ΔSNOW, a semi-empirical approach to derive daily SWE exclusively from consecutive HS series.

The ΔSNOW model - freely available as part of the R-package “nixmass” - builds on basic snow physics and needs seven parameters. If available, those should be fitted using SWE measured at the respective HS observation site(s), otherwise a standard set of parameters is provided, which was calibrated with data from the Alps. In the current model version, the parameters are kept unchanged over time. New-snow density and the maximum density model layers can reach are among the parameters. For natural snow, those vary significantly from day to day and during the winter season, also site specifics like, e.g., altitude influence them.

With this contribution the restriction of fixed density parameters in the ΔSNOW model is probed. Improvements might be achieved if new-snow density was made dependent on the amount of freshly fallen snow, rather than on altitude, date or region. The model-intrinsic maximum snow density could probably be improved if it was increased by the age of the respective snow layers as well as the overburden mass of snow. All validation experiments were performed with SWE and HS data from the Alps and from Germany. The latter comprising a huge high quality data set not only from mountainous regions but also from lowlands and maritime regions. The ΔSNOW model`s ability to simulate daily SWE outperforms other models of comparable complexity also in these areas, even more with adjusted density parameters.
Inconsistency in Precise Point Positioning products from GPS, GLONASS and Galileo 
Authors: Zajdel Radosław , Kazmierski Kamil , Sośnica Krzysztof
Published: March 2022

Global Navigation Satellite Systems (GNSSs) are widely used for Earth system monitoring, e.g., solid earth and atmosphere. However, the time series of station coordinates and zenith tropospheric delay derived using GNSS are inherently affected by several technique-specific errors that influence the interpretation of geophysical processes and phenomena. GPS plays a crucial role and is most often used in interdisciplinary studies. However, the multiplicity of navigation systems, including fully operational GLONASS and Galileo, allowed us to assess system-specific high-frequency signals and inconsistencies arising from using different constellations.

This work shows that using different GNSS constellations leads to the appearance of various artificial signals with amplitudes up to several millimeters in the series of station coordinates. The presence of the GNSS system-specific artifacts and inter-system disagreements are demonstrated using the 2-year long series of station coordinates and zenith total delay parameters for 15 stations using Precise Point Positioning algorithms. Finally, we assessed the benefit of using GPS, GLONASS, and Galileo jointly.

We identified the origin of the spurious signals in orbital errors. The most dominant orbital artifacts for Galileo appear with periods of 14.08 h, 17.09 h, 34.20 h, 2.49 d, ~3.4 d. The corresponding signals for GLONASS appear with periods of 5.63 h, 7.36 h, 10.64 h, 21.26 h, 3.99 d, and ~8 d. Moreover, when estimating discrete 24-hour solutions from high-rate GNSS data, high-frequency signatures are under-sampled, resulting in long-term aliased periodic signals. The GPS orbital signals arise at the periods corresponding to the harmonics of the K1 tide, which leads to the inconsistency of the GPS-based products with ocean tidal loading models reaching on average 12 mm for the K2 tidal term in the Up component. The magnitude of the orbital signals varies between different site locations and depends on the GNSS observation geometry and dominant direction of satellites' flybys. For example, because of the high inclination of the GLONASS orbital planes, the stations located in absolute low latitudes observe mostly North-South satellite flybys; thus, the estimated East component of the coordinates is exposed to the orbital artifacts.

Galileo is less vulnerable to the orbital signals than GPS or GLONASS. The difference is visible mainly for the East coordinate component. The Galileo-based daily estimates are up to 55% and 36% better than those delivered from GLONASS and GPS. Finally, using a combination of GPS and Galileo increases the precision of estimates by 10% compared with the best-case Galileo-only solution and remarkably reduces the system-specific errors in station coordinate time series.
3D structural analysis of the cave of Saint Michael at Minervino Murge, Bari (Italy) – a typical case of karst environment in Puglia
Authors: Cardia Stefano , Langella Francesco , Pagano Marco , Palma Biagio , Parise Mario
Published: March 2022

The presence of surface and subterranean landforms (caves, sinkholes, etc.) produced by karst processes in the Apulian territory is among the most typical features of the local landscape. Numerous examples can be counted throughout the region, especially in the Murge plateau, one of the three karst sub-regions of Apulia. Here the rock, being composed mainly of carbonates, has been affected in multiple stages by karst, which more visible results nowadays consist of numerous cavities, some of which show evidence of instability problems. At the present day, especially for those caves which are open to the public, it is necessary to perform stability analysis aimed at evaluating the stability conditions at the sites. In the Murge area, the cave of Saint Michael at Minervino Murge is among the most famous, belonging to the set of caves dedicated to the figure of Saint Michael the Archangel, which also includes the UNESCO protected site at Monte Sant’Angelo, in the Gargano Promontory of northern Apulia, a major Catholic pilgrimage site. At Minervino Murge, the cave consists of a wide room hosting a deep and wide stairway leading to the altar dedicated to Saint Michael, and an innermost, smaller, environment which entirely keeps its naturality. Besides the religious and historical interests, the whole cave needs a detailed analysis of the stability of the rock mass, both for the protection of its architectural and archaeological values and for the safeguard of the pilgrims. At this aim, we performed various digital surveys by means of laser scanners and drones equipped with high-resolution cameras. The results of these scans are going to be processed in order to understand the geometry of the entire cave and to properly determine the main volumes of unstable blocks, as well as the likely kinematics of movement. Given the height of the cave, remote sensing techniques are particularly suitable for such an analysis, allowing to obtain from a distance the relevant data, rather than investigating the site with traditional geomechanical survey methods. Furthermore, the facility of acquisition of the remote sensing data will allow repetitiveness of the surveys, thus permitting monitoring over different time windows, in order to check periodically the most dangerous situations and to properly exploit this site of historical importance and religious worship.
Effects of historic changes in regional drainage characteristics on the drawdown of groundwater abstractions
Authors: van Huijgevoort Marjolein , Cirkel Gijsbert , Bartholomeus Ruud
Published: March 2022

Calculating the drawdown of groundwater abstractions for drinking water is usually done considering the current land use and regional drainage characteristics. However, many drinking water abstractions already exist for several decades and abstracted volumes have increased over time. In the Netherlands, especially in the more elevated parts of the country, the drainage characteristics were also significantly altered to prevent water logging and to optimize the water management for agricultural use, often after establishment of the groundwater abstraction site. These changes were intended to lower the phreatic groundwater levels to prevent waterlogging, but unintendedly also made the regions more vulnerable to drought. The question is whether groundwater abstractions for groundwater would have a similar impact in the former historic hydrological context and whether restoring the system to this state would ameliorate current drought problems.

In this study we investigated whether a drinking water abstraction would have the same drawdown if the regional drainage characteristics would not have been altered and whether restoring the historic situation would decrease drought impacts. First, a literature study was conducted to understand the changes to the drainage system over time. These changes were then implemented in a regional groundwater model (based on Modflow) for a conceptual region, representative for the eastern part of the Netherlands. Results from both the literature study and the groundwater model indicated that changes in the drainage system lowered the groundwater levels by tens of centimetres (differences ranged from 20 to 100 cm). Drawdown from the drinking water abstraction was larger in the historical situation than in the current situation, even though groundwater levels were higher. In the historical situation less reduction in transpiration occurred, leading to a lower recharge of the groundwater and thus a larger drawdown. However, when irrigation was applied, this effect was not found.  This implied that a correct estimate of groundwater recharge is crucial to calculate drawdown from abstractions. Recharge depends on actual evapotranspiration, of which the conceptualization in regional models could be improved. Returning the drainage system to the historical situation leads to higher groundwater levels, thereby reducing the drought impact, but also increasing the risk of oxygen stress in crops. More research with regard to the impact on crop yields is needed on local scale, before measures to mitigate drought impacts can be taken.
Reexamining the temporal and spatial patterns of exhumation and erosion in the Northern Apennines: new insights from low-temperature thermochronometers
Authors: Erlanger Erica , Fellin Maria Giuditta , Willett Sean
Published: March 2022

We present published bedrock apatite fission track (AFT) and apatite (U-Th)/He (AHe) ages from the Northern Apennines to provide new insights into the spatial and temporal pattern of erosion across the mountain range. The spatial pattern of time-averaged erosion rates derived from AFT ages illustrates similar erosion rates on the Ligurian and Adriatic sides of the range. However, erosion rates derived from AHe ages are higher on the Adriatic side of the range, relative to the Ligurian side. The temporal pattern of time-averaged erosion rates illustrates an overall decrease in erosion through time on the Ligurian side, but suggests an increase in erosion through time on the Adriatic side. These results are corroborated by an analysis of paired AFT and AHe thermochronometer samples, which illustrate that erosion rates have generally increased through time on the Adriatic side, but have decreased through time on the Ligurian side. We infer that such regional scale-differences must be controlled by first-order features of the Northern Apennines, so we present an updated kinematic model to understand what could control these differences. Using imposed erosion rates on the Ligurian side that are a factor of two slower relative to the Adriatic side, we demonstrate that cooling ages and maximum burial depths are able to replicate the pattern of measured cooling ages across the orogen and estimates of burial depth from vitrinite reflectance data. These results suggest that horizontal motion is an important component of the overall rock motion in the wedge, and that the asymmetry of the orogen has existed for at least several million years.
The influence of sedimentary heterogeneity on the diffusion of radionuclides in the sandy facies of Opalinus Clay at the geological scale
Authors: Chen Chaofan , Yuan Tao , Lu Renchao , Fischer Cornelius , Montoya Vanessa , Kolditz Olaf , Shao Haibing
Published: March 2022

Radionuclide migration in clay-rich formations is dominated by molecular diffusion due to the low permeability of the claystone. Accurate estimation of radionuclide migration in host rock using numerical tools plays a key role in the safety assessment of disposal concepts for nuclear waste. In the sandy facies of the Opalinus Clay (SF-OPA), the spatial variabilities of the pore network and compositional heterogeneities at the pore scale (nm to µm) cause heterogeneous diffusion at the core scale (cm to dm). Such heterogeneous diffusion patterns affect the migration of radionuclides in the various sedimentary layers even above the core scale (~m). Small-scale heterogeneities of diffusive transport could play an important role in upscaling to larger length scales of SF-OPA, particularly because of differences in sedimentary and diagenetic facies. Therefore, a meaningful estimation of radionuclide migration in the host rock above the core scale requires a comprehensive study of the influence of sedimentary layers on the heterogeneous diffusion.

In this work, we study the heterogeneous diffusion of radionuclides based on a two-dimensional (2D) structural model from the geological data of SF-OPA in the Mont Terri rock laboratory at the m-scale. As key parameters for the diffusive transport calculation, the effective diffusion coefficients in different sedimentary layers are quantified based on the developed upscaling workflow from pore- to core-scale simulation combined with the multi-scale digital rock models [1]. The heterogeneous effective diffusivities are then implemented into the large-scale structural model for diffusive transport simulation using the FEM-based OpenGeoSys-6 simulator. Results show that the various heterogeneous effective diffusivities under different mesh resolution (length scales) in the large-scale simulations strongly affect the evolution of radionuclides concentration in SF-OPA, especially in the vicinity of the canister. The sensitivity analysis focuses on the effects of length, bedding angle and thickness of the sedimentary layer on the spatio-temporal evolution of radionuclide concentrations. The numerical results provide insight into the heterogeneous diffusion of radionuclides, contributing to enhanced long-term predictability of radionuclide migration in the host rock of the deep geological repository.

[1] Yuan, Tao, and Cornelius Fischer. "Effective Diffusivity Prediction of Radionuclides in Clay Formations Using an Integrated Upscaling Workflow." Transport in Porous Media 138.2 (2021): 245-264.
Tracing N2O formation in full-scale wastewater treatment with natural abundance isotopes
Authors: Mohn Joachim , Gruber Wenzel , Magyar Paul , Zeyer Kerstin , von Känel Luzia , Morgenroth Eberhard , Lehmann Moritz F. , Braun Daniel , Joss Adriano
Published: March 2022

Nitrous oxide (N2O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N2O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N2O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N2O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have never been applied to full-scale WWTPs.

Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N2O monitoring, allow identification of the N2O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). The proposed approach can also be applied to other activated sludge systems. Heterotrophic denitrification appears as the main N2O production pathway under all tested process conditions, while nitrifier denitrification was less important, and more variable. N2O production by hydroxylamine oxidation was not observed. Fractional N2O elimination by reduction to dinitrogen (N2) during anoxic conditions was clearly indicated by a concomitant increase in SP, δ18O(N2O) and δ15N(N2O). The extent of N2O reduction correlated with the availability of dissolved inorganic N and organic substrates, which explains the link between diurnal N2O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavourable, as it is very likely to cause high net N2O emissions.

Our results demonstrate that monitoring of the N2O isotopic composition holds a high potential to disentangle N2O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modelling of N2O formation or microbial assays to develop efficient N2O mitigation strategies.
Shallow-water hydrothermal venting in the North Atlantic during the Paleocene Eocene Thermal Maximum 
Authors: Berndt Christian , Planke Sverre , Alvarez Zarikian Carlos , Bünz Stefan , Karstens Jens , Svensen Henrik , Manton Ben ,   IODP Expedition 396 Scientific Party
Published: March 2022

The Paleocene Eocene Thermal Maximum (PETM, ~56 Ma) was a rapid global warming of 5-6 ºC resulting from massive (>2000 Gigatons) carbon emissions. A potential release mechanism is thermogenic gas from contact metamorphism of carbon-bearing sediments due to magma intrusions into sedimentary basins. Here, we present seismic data and borehole information from the North Atlantic Igneous Province. They show that even in the center of the rift system, water depths were sufficiently shallow to allow most gas released from hydrothermal vent systems to bypass the water column. The shape of the vent craters and stratified infill suggest vigorous explosive gas release during the initial phase of vent formation and rapid shallow marine and largely undisturbed infill thereafter. The recorded negative carbon isotope excursion and occurrence of the index taxon Apectodinium augustum in the crater-infill support assignment to a latest Paleocene to earliest Eocene vent formation. The data support a scenario where magmatic sill emplacement and resulting hydrothermal activity rapidly injected thermogenic greenhouse gas into the atmosphere.
Statistics of transpolar arcs identified by an automated detection algorithm
Authors: Bower Gemma , Milan Steve , Paxton Larry , Imber Suzie
Published: March 2022

Transpolar arcs (TPAs) are auroral features that occur polewards of the main auroral oval, at latitudes where auroras are less common, suggesting that the magnetosphere has acquired a complicated magnetic topology. They are primarily a northward interplanetary magnetic field auroral phenomenon, and their formation and evolution have no single explanation that is unanimously agreed upon. An automated detection algorithm has been developed to detect the occurrence of TPAs in UV images captured by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument onboard the Defense Meteorological Satellite Program (DMSP) spacecraft, in order to further study their occurrence. Via this detection algorithm TPAs are identified as a peak in the average radiance intensity above 12.5° colatitude, in two or more of the wavelengths/bands sensed by SSUSI.

Using the detection algorithm on observations from the years 2010 to 2016, over 5000 images containing TPAs are identified. The occurrence of these TPA images suggest a seasonal dependence, with more TPAs observed in the winter hemisphere. The orbital plane of DMSP has been investigated as a possible explanation of the dependences in the results of the detection algorithm. It has been found that each DMSP spacecraft has a different bias due to its orbit. For the spacecraft of interest (F16, F17 and F18) this leads to a preferential observation of the northern hemisphere, with the detection algorithm missing TPAs in the southern hemisphere around 01 - 06 UT. No seasonal bias has been found for these spacecraft.

We also discover that the majority of TPAs occur in the dawn sector of the polar cap, which is unexpected in current TPA models. Comparing with previous statistical surveys, we note that the dawn-dusk asymmetry has been present but has not gained significant attention.  We suggest that field-aligned current polarity may play a role in the observed asymmetry.

We discuss the ramifications of these findings in terms of proposed TPA generation mechanisms and suggest reasons for the seasonal dependence including it being a reflection of probability of seeing TPAs due to visibility.
The effect of cadmium on calcium carbonate growth and dissolution
Authors: Julia Maude , V.Putnis Christine , E.King Helen , Renard François
Published: March 2022

Calcium carbonates are ubiquitous minerals in nature and have been recently studied for potential environmental remediation as a toxic element retainer following reaction with contaminated water. This work aims to study the effect of cadmium ions, a major pollutant in soil and waterways, on calcium carbonate dissolution and growth using different experimental and analytical methods. Firstly, calcite growth and dissolution in the presence of varied Cd2+ concentrations have been observed with in situ atomic force microscopy (AFM). Then hydrothermal experiments have been conducted to compare calcite and Carrara marble samples to study the effect of grain boundaries on calcium carbonate dissolution in the presence of solutions containing Cd2+. Results indicate that a new (Ca,Cd)CO3 phase is formed on the calcite surfaces that become increasingly covered and possibly passivated by the presence of this new layer. This is observed in both the AFM experiments as well as hydrothermal experiments using calcite crystals. However, the grain boundaries within Carrara marble act as fluid pathways within the rock allowing access for the Cd – rich solutions to penetrate within the sample. Surface passivation compared with coupled dissolution-precipitation replacement reactions are investigated in terms of molar volume changes and solubility differences between parent (CaCO3) and product ((Ca,Cd)CO3) phases as well as reaction kinetic considerations.
The Interaction of Internal Solitary Waves and Sea Ice in the laboratory
Authors: Hartharn-Evans Sam , Carr Magda
Published: March 2022

Internal Waves are commonly observed along density interfaces across the world’s oceans. In the Arctic Ocean, the internal wave field is much less energetic than at lower latitudes, but due to relative quiescence of the region, nonlinear internal waves are particularly important for mixing there. This mixing is responsible for bringing heat from warm Atlantic Water at intermediate depth towards the surface where it has ramifications for the formation and melt of sea ice, as well as the general circulation of the Arctic Ocean. In the rapidly changing Arctic Ocean, as sea ice extent declines, understanding how internal waves interact with sea ice, and how sea ice affects them is crucial, particularly in the marginal ice zone.

Using laboratory experiments of internal solitary waves (ISWs) propagating under model ice the interaction of ice and internal solitary waves is investigated. Specifically, (i) Particle Tracking Velocimetry is used to measure the motion of floating discs (with the same density as sea ice ρ = 910kg/m³), to determine how ice moves in response to the near-surface internal wave-induced flow using is quantified. Additionally, (ii) Particle Image Velocimetry is used to determine how the near-surface internal wave-induced flow dynamics are impacted by the presence and motion of the model sea-ice, which acts as a rough upper boundary condition and moves with the flow.
Imaging inner core anisotropy using normal mode and body wave data
Authors: Brett Henry , Hawkins Rhys , Waszek Lauren , Lythgoe Karen , Deuss Arwen
Published: March 2022

The Earth's inner core displays strong seismic anisotropy and 3D heterogeneity, which are most likely formed as a result of growth processes and post solidification deformation. Thus, accurately resolving seismic anomalies is key to understanding the formation and dynamic mechanisms of the inner core. Our ultimate aim is to improve current constraints on seismic anomalies in the inner core by combining normal mode data and body wave data in a joint tomographic inversion. While the body wave data is sensitive to regional scale seismic P-wave anisotropy in the inner core, normal modes provide long wavelength information on density, P-wave anisotropy and S-wave anisotropy. 

We have produced a high resolution 3D seismic model of inner core isotropic and anisotropic velocity variations using a transdimensional methodology with body waves. In the transdimensional approach, the inversion itself determines the parameterization. It is encouraging to find many well know features, such as a hemispherical differences between a slow and strongly anisotropic western region and a fast and only weakly anisotropic eastern hemisphere, without a priori imposing those in our parameterization. We are now interested to see if the features seen using body waves are consistent with those seen by normal modes. We measure inner core sensitive normal modes using the splitting function approximation in a way which thoroughly explores the splitting function measurement model space. This then allows us to quantify the uncertainty in individual splitting function coefficients for each mode. We then combine these new normal mode measurements and uncertainty estimates with our body wave data in a joint probabilistic inversion for seismic structure in the inner core.
Which are the largest glaciers in the world outside the ice sheets?
Authors: Zemp Michael , Windnagel Ann , Hock Regine , Maussion Fabien , Paul Frank , Rastner Philipp , Raup Bruce
Published: March 2022

Glacier monitoring has been internationally coordinated for more than 125 years. Despite this long history there is no unambiguous answer to the popular question: which are the world’s largest glaciers?

In this study, we present a first scientific assessment of the largest glaciers in the world – distinct from the two ice sheets in Greenland and Antarctica – and in the 19 regions used for the current Randolph Glacier Inventory. Ranking glaciers by size is non-trivial since it depends on how an individual glacier is defined and mapped. It is also important to differentiate between individual glaciers and glacier complexes, which are contiguous glaciers that meet at ice divides and might form an ice cap or ice field.

We find that the largest glacier complexes cover areas larger than ten thousand square kilometres, whereas the largest individual glaciers cover up to several thousand square kilometres. The world’s largest glaciers and glacier complexes are located on the Antarctic Peninsula, on sub-Antarctic Islands, in the Arctic, and in Patagonia. As such, the largest glacier complexes cover areas the size of smaller countries (e.g., Switzerland or Austria) or of smaller US states (e.g. New Jersey or South Carolina), but are still orders of magnitudes smaller than the Greenland and Antarctic Ice Sheets.

In addition, we show that the ranking of glaciers requires not only clear definitions but depends on the availability, quality, and consistency of digital glacier outlines at global scale. Corresponding additional metadata are required in the available inventories to fully automate a glacier ranking by area, and to extend such a study to rankings by length, volume/mass, and other parameters.