bluuebunny/crossref_metadata_2025 huggingface dataset:
What role do glaciers play in smoothing streamflow during summer rainfall events? A case study from the Swiss Alps.
Authors: Schaefli Bettina , Binkert Ladina , Benelli Luca , Ceperley Natalie , Leiser Peter , Baumgartner Jan , Berger Benjamin , Wyss Kevin
Published: March 2022

The retreat of glaciers, particularly in catchments where they were extensive, has important consequences for future water management and in particular for hydropower production. Glaciers store water in liquid or solid form on short- to long-term time scales and thereby affect the precipitation-runoff behavior of heavily glacier-covered catchments from interannual and seasonal to sub-daily time scales. While today reliable predictions can be made about the change in quantity and timing of glacier melt runoff, the consequences of glacier retreat for summer rainfall events remain unclear. By intensively monitoring streamflow during the summer months in an area with a high degree of glacier cover, we can fill this research gap. Our key research question is hereby how strongly the glacier smooths out the observed rainfall peaks and how the smoothing effect evolves over the course of the glacier melt season. The answer to this question is crucial to anticipate potential water and sediment management challenges under intense summer rainfall events in catchments with strongly reduced glacier-cover.

In this presentation, we share results from the Oberaargletscher catchment (10 km2, elevation 2310 - 3630 m a.s.l.) located in the Swiss Alps that was intensively monitored from July to October 2021. The monitored variables include precipitation, streamflow, electric conductivity, stable isotopes of water, water and air temperature. Based on the high resolution streamflow data, we analyze the influence of summer rainfall events on the runoff response, and in particular on the runoff lag time and the hydrograph shape. The obtained results are related to potential driving variables including the extent of snow cover and of the glacial drainage system, the precipitation intensity and air temperature.

We will furthermore discuss to what extent the rainfall fraction in the streamflow can be quantified based on streamflow observations alone, which will give valuable insights for future measurement campaigns at comparable sites.
Disentangling Internal and External Contribution to Atlantic Multidecadal Variability over Past Millennium
Authors: Fang Shih-Wei , Khodri Myriam , Timmreck Claudia , Zanchettin Davide , Jungclaus Johann
Published: March 2022

The Atlantic Multidecadal Variability (AMV) modulates the North Atlantic surface ocean variability and affects decadal climate evolution up to the global scale; however, the underlying mechanisms of the AMV remains debated. We use a multi-model ensemble of transient past-millennium and unperturbed preindustrial control simulations contributing to the Paleoclimate Modelling Intercomparison Project - Phase 4 (PMIP4) to decompose the AMV signal into its internal and external components. The internal component of AMV exhibits no robust behavior across simulations during periods of major forcing such as strong volcanic eruptions, whereas the externally-forced component of AMV responds to volcanic eruptions with an immediate radiative cooling followed, in some simulations, by a sequence of damped multidecadal oscillations. This indicates that the intrinsic mechanism underlying the AMV is distinguishable from its response to external forcing. The internal component of AMV is tightly connected with the Atlantic meridional overturning circulation (AMOC) and controls the variations of AMV. The external component of AMV explains about 25% of the variance in the past millennium simulations, though less-consistency is found between models. Our results further indicate that the spatial imprint of external volcanic forcing on North Atlantic sea-surface temperatures differs from the surface pattern of the internal AMV contributing to the lack of robustness for the AMV pattern.
Modelling Transverse Anomalous Solute Transport in Highly Heterogeneous Porous Media
Authors: Dell'Oca Aronne , Dentz Marco
Published: March 2022

We study the intermittent transverse dynamics of solute transport through highly heterogeneous porous media.  Considering a Lagrangian framework focused on the equidistantly analysis of the particles motion, we identify two fundamental mechanisms that determine large scale particle motion, amely, the relaxation towards an (non-zero) average transverse particle position and the short-scale correlated behavior of the transverse particles motion. Based on these mechanisms, we derive a theory that jointly predicts anomalous transverse and longitudinal dispersion in terms of Eulerian velocity distribution, key statistics of the system heterogeneity and two additional parameters related to the particles relaxation process with a clear physical meaning.
Real-time spatial O2-sensing in 2D porous media to investigate conditions for anoxic micro-niches onset and microbial facultative metabolism trigger.
Authors: Ceriotti Giulia , Borisov Sergey , Berg Jasmine , de Anna Pietro
Published: March 2022

The heterogeneous spatial organization and composition of bacterial communities in soils are expected to deeply impact geochemical quantities at the pore-scale, shaping steep solutes gradients in spite of mixing processes. Oxygen distribution is of major interest since localized anoxic niches might host facultatively anaerobic bacteria. This means that metabolisms alternative to aerobic respiration might be triggered even in well-oxygenated systems, thus largely impacting soil ecological functions.

Our ability to non-invasively monitor O2 time-space distributions at the scale of interest for bacterial clusters is still limited. Moreover, the identification of the critical O2 level at which facultative bacteria switch their metabolism is little explored and largely debated. 

This work presents an innovative experimental setup allowing to simultaneously quantify oxygen concentrations and biomass arrangement as a function of time and space in microfluidic devices, which mimic natural porous media. Our methodology makes use of i) a newly developed and customized planar transparent fluorescent sensor whose fluorescence intensity is sensitive to oxygen concentration, and ii) a fully automated microscope to collect high-resolution large images.

Our results reveal that microbial aggregates and oxygen distribution are closely correlated both spatially and temporally demonstrating that microbial activity can generate and sustain anoxic micro-niches. This anoxic space occupies up to 2-3 % of the porous volume and is controlled by the competition between advective/diffusive processes (supplying oxygen) and microbial O2 consumption. Interestingly, bacterial cluster shapes and their spatial organization are key elements determining the development of anoxic micro-niches and their impact on macroscale processes. Based on the new insights provided by our experiment, we develop an original definition of Damköhler number to describe the conditions for anoxic micro-niches onset under the laminar diffusion-dominated flow that typically characterized groundwater systems.

This novel methodology combined with opportunely tagged laboratory strains opens new frontiers to investigate the O2 critical concentration associated with facultative metabolism trigger for bacteria with interesting function in soil ecology and wastewater water and drinking water remediation engineering.
From Magnetic Reconnection at Chromospheric Network Boundaries to Switchbacks in the Inner Heliosphere
Authors: Hou Chuanpeng , He Jiansen , Duan Die , Li Huichao , Chen Yajie
Published: March 2022

During its perihelion encounter, Parker Solar Probe (PSP) has observed abundant kink and switchback patterns of magnetic field lines in the young solar wind. Such switchback structures have gained widespread attention due to their manifestation of Alfvenic and compressional properties, such as velocity enhancement, plasma density, and temperature variation. In particular, the origin mechanism has been a hot topic and waits to be observationally confirmed. Here we use a two-step ballistic backmapping method (tracing along the Parker Spiral and the PFSS-solution extrapolated from the GONG synoptic magnetogram) to determine the foot-points of the magnetic lines during switchback events measured by PSP on 24th-27th Jan. 2020. We identify ten jets corresponding to the PSP-switchbacks and find relevance between jets and switchback patches. We find that jets excite at the height of around low corona and position of chromospheric network boundaries. About 70% of jets accompany a magnetic cancelation, while 30% of jets are related to magnetic emergence. The variation in magnetic flux corresponding to magnetic cancelation and magnetic emergence is quantitatively equal to that of radial magnetic flux associated with switchback patches. These features suggest that switchbacks may originate from an interchange magnetic reconnection at chromospheric network boundaries, which provides direct evidence of switchbacks' solar origin. 
Tracing sediment movement using Infra-Red Stimulated Luminescence
Authors: Spano Tessa M. C. , Rhodes Edward J. , Hodge Rebecca A.
Published: March 2022

Understanding sediment transport dynamics is key to understanding landscape evolution, and has important implications for engineering projects, aquatic ecosystem dynamics, and transmission of water-borne diseases. Multiple elevated temperature infra-red stimulated luminescence (MET-IRSL) has great potential to provide detailed information on the transport of sediments using infra-red light to stimulate the luminescence signal of feldspars. MET-IRSL uses a series of elevated temperature stimulations to access multiple signals with different characteristic rates of signal reduction by light exposure (bleaching), for example, during grain transport. During deposition and storage, trapped charge accumulates, leading to growth of the different IRSL signals, until the grain is again subject to transport. Applied in this manner, MET-IRSL measurements can constrain past sediment burial and exposure histories.

MET-IRSL measurements of different grain and clast sizes (e.g. silt, sand, pebbles and cobbles) can provide a range of sediment transport information, providing further constraint to sediment dynamics and system behaviour. Different clast size groups are associated with varied ways to structure the MET-IRSL measurements, e.g. depth bleaching profiles observed within pebbles and cobbles. In this presentation we demonstrate the potential of combining these approaches, and of constructing time-space equivalence models for real world situations, including the site of Allt Dubhaig, Perthshire, Scotland.
Increased warm water intrusions would cause mass loss in East Antarctica within 200 years
Authors: Jordan Jim , Gudmundsson Hilmar , Jenkins Adrian , Miles Bertie , Stokes Chris , Jamieson Stewart
Published: March 2022

Increased warm water intrusions would cause mass loss in East Antarctica within 200 years

The East Antarctic Ice Sheet (EAIS) is the single largest potential contributor to future global mean sea level rise, containing 52.2 m of sea level equivalent. Current observations put the mass balance of the EAIS to be approximately stable (albeit with some margin of error), although future climatic conditions have the potential to change this. A warming climate is expected to have both a positive effect on ice sheet mass balance via increased precipitation and a negative effect via increased ice discharge over the grounding line, a process enhanced by ocean driven melting of floating ice reducing the buttressing effect of ice shelves. In addition to a general increase in the ocean temperature surrounding the EAIS there is the potential that future climatic shifts may increase the incidence of intrusions of warm Circumpolar Deep Water (CDW) onto the continental shelf, further increasing basal melting.

Here we show, by using a numerical ice-sheet model, simulations of the future EAIS under different  future climate scenarios, both with and without increased CDW intrusions. We find that without increased CDW intrusions the EAIS will have a negative contribution to sea level rise, with increased precipitation more than compensating increased ice discharge. If melting becomes predominately driven by CDW, however, our simulations find the EAIS to have a positive contribution to sea level rise. All simulations, both those with increased CDW forcing and those without, show an overall reduction in floating ice as well as a reduction in grounded ice area.
Interannual Variability of Arctic Climate: Seasonal and Regional Disparities
Authors: Kolbe Marlen , Bintanja Richard , van der Linden Eveline
Published: March 2022

The future of year-to-year variability of Arctic climate change indicators such as sea ice and precipitation is still fairly uncertain. Alongside climatic changes in means, a thorough understanding of interannual variability (IAV) is needed to accurately distinguish between signal and underlying noise, as well as to describe the likelihood of extreme events. 

In this study we quantify the IAV of Arctic surface air temperature, precipitation, evaporation, and sea ice area from 1851-2100 as a function of time in order to assess the effect of climate change on future variability. By influencing the likelihood of extreme events, changes in the magnitude of IAV can not only influence the surface mass balance of the Greenland Ice Sheet, but also affect regions in lower latitudes. Investigations of global climate model output strongly suggest that intermodel differences in CMIP6 projections of IAV are largely explained by natural variability versus model physics. Our results further highlight the need to distinguish between seasons as well as regions when investigating past, present and future states of IAV of Arctic climate. For example, increases in precipitation variability will become much more significant and intense in winter (after 2040) and most pronounced in coastal regions near the Bering Strait, the GrIS and the Norwegian Sea. Depending on the season, the retreat of sea ice can alter precipitation patterns through the process of enhanced evaporation over open ocean areas. Sea ice variability can therefore explain regional and seasonal changes of the Arctic water cycle, as it shifts from being snow- to rain-dominated.
Developing a new space sector careers resource based on educational research recommendations
Authors: Archer Martin , Waters Cara , Dewan Shafiat , Foster Simon , Portas Antonio
Published: March 2022

Educational research shows participation issues across Science Technology Engineering and Mathematics (STEM) are due to whether students see these fields and their potential career opportunities as for “people like me”. These perceptions form early and remain relatively stable with age, which has led to recommendations for increased provision and quality of careers education/engagement at both primary and secondary levels. Space-related roles should be rife for inclusion in careers education resources. However, we find that current UK careers resources concerning the space sector do not perhaps best reflect the diversity of roles present and may in fact perpetuate misconceptions about the usefulness of science. We present the development process of a new space careers resource, detailing how we have attempted to improve the diversity of space-related careers highlighted as well as addressing the key issues and recommendations raised by recent educational research.
How to detect slow slip and long-term seafloor deformation? Lessons from two acoustic ranging campaigns on the submerged flank of Mt Etna
Authors: Petersen Florian , Urlaub Morelia , Gross Felix , Bonforte Alessandro , Kopp Heidrun
Published: March 2022

The Earth’s ocean floor deforms continuously under the influence of tectonic and non-tectonic processes. In the recent decade, the installation of seafloor geodetic instruments to accurately monitor fault displacement and strain accumulation has greatly improved our understanding of seafloor deformation and our knowledge of associated offshore hazards. In particular, the application of acoustic direct-path ranging networks allows the detection of displacement and strain accumulation of faults in millimeter-level precision.

On-land geodetic networks revealed that the Southeast flank of Mount Etna slides seawards at a rate of ~3 cm/yrs. The highest rates are observed near the coast and the volcano flank extends far into the Ionian Sea. The long-term deformation is superimposed by frequent slow-slip events with up to ~3 cm displacement. Our first acoustic ranging measurements between 2016 and 2018 confirmed offshore active deformation and seafloor displacement by detecting a slow-event of up to ~4 cm with a right-lateral offset. Thus, the application of direct-path ranging transponders has proven to be a promising tool to monitor horizontal and vertical displacement of such strike-slip fault zones. However, the observation of long-term deformation, as observed on onshore faults, is lacking. Therefore, we conducted a second acoustic geodetic deployment at the same site offshore Mount Etna between September 2020 and November 2021 and used a different network design. The new data set shows an indication for slow long-term seafloor deformation, which had not been resolved in the first deployment. By comparing the different configurations of the acoustic direct-path networks we were able to improve data processing to achieve millimeter-level precision. We have learned that longer-distance measurements over a sharp fault favor the detection of slow-slip events, but impede the observation of slow long-term deformation. In order to resolve the latter movement, very short baselines close to the fault trace are ideal. Therefore, a trade-off between long and short-distance measurements might be the key for compressive deformation monitoring. Our results prove that the direct-path acoustic ranging technique is well-suited to detect different styles of fault slip at faults with sharp surface traces.
GESLA Version 3: A major update to the global higher-frequency sea-level dataset
Authors: Haigh Ivan D. , Marcos Marta , Talke Stefan A. , Woodworth Philip L. , Hunter John R. , Hague Ben S. , Arns Arne , Bradshaw Elizabeth , Thompson Philip
Published: March 2022

This paper describes a major update to the quasi-global, higher-frequency sea-level dataset known as GESLA (Global Extreme Sea Level Analysis). Versions 1 (released 2009) and 2 (released 2016) of the dataset have been used in many published studies, across a wide range of oceanographic and coastal engineering-related investigations concerned with evaluating tides, storm surges, extreme sea levels and other related processes. The third version of the dataset (released 2021), presented here, contains twice the number of years of data (91,021), and nearly four times the number of records (5,119), compared to version 2. The dataset consists of records obtained from multiple sources around the world. This paper describes the assembly of the dataset, its processing and its format, and outlines potential future improvements. The dataset is available from https://www.gesla.org.
A biogeochemical approach to build a perceptual hydrological model for a small peri-urban catchment
Authors: Grandjouan Olivier , Branger Flora , Masson Matthieu , Cournoyer Benoit , Coquery Marina
Published: March 2022

The origin and transport of water in peri-urban catchments is complex to model as they are affected by multiple anthropogenic modifications of water pathways (surface imperviousness, sewer overflow releases…), especially in a context of fast growing urbanization. The hydrological dynamics are also  impacted by natural and agricultural land use patterns. Perceptual models aim at reproducing our understanding of a catchment behaviour and can be useful to illustrate the impact of such spatial contrast and human-induced modifications on a catchment hydrological dynamics. Conservative geochemical and microbiological tracers can be linked to the hydrological processes and water pathways to enhance this understanding and to build-up the hydrological perceptual model of a catchment.

From 2017 to 2019, a monthly monitoring of geochemical and microbiological tracers was conducted at the Ratier catchment (19 km²) near Lyon (France). Surface waters were collected and analysed for major chemical parameters (cations, anions, dissolved organic carbon and conductivity), dissolved metals, stable isotopes (2H et 18O), and microbial parameters (total bacterial counts, microbial source tracking DNA datasets, species – specific DNA trackings). Using these datasets, a step-by-step statistical approach was undertaken, and used to build-up the perceptual hydrological model. The main steps were: (1) group correlated biochemical parameters to reduce redundancy in the dataset, (2) compute the main indicators illustrating the hydro-climatologic dynamics during the sampling campaigns (e.g. antecedent index precipitation, average daily flow) based on the hypothesis of a two-component catchment (groundwater and subsurface flow), and (3) perform a principal component analysis to link the biogeochemical dataset to the computed hydro-climatologic indicators and the runoff processes.

Results revealed a differentiation of the datasets in two groups matching groundwaters and subsurface waters. Groundwaters showed two geochemical profiles linked to the two main geological formations of the catchment. Subsurface waters showed more variable biogeochemical patterns highly influenced by land use and soil properties. This step-by-step statistical approach led to a better understanding of the dynamics of the water pathways and these insights were then used to build-up the hydrological perceptual model of the catchment. As a next step, such a model should help in the evaluation and improvement of a distributed hydrological model.
Numerical reconstructions of the Patagonian Ice Sheet: Growth and demise through the Late Quaternary
Authors: Castillo Andrés , Prange Matthias , Bernales Jorjo , Retamal-Ramírez Franco , Schulz Michael , Rogozhina Irina
Published: March 2022

Glacial geomorphological and geochronological studies suggest that the Patagonian Ice Sheet (PIS) stretched from 38°S to 55°S during the Marine Isotope Stages (MIS) 2-3. While its western margin reached the Pacific Ocean, the easternmost sectors of the PIS were characterized by terrestrial lobes that fed large paleo glacial lakes after its maximum extension towards the end of the MIS 3. An ice-marginal stabilization occurred throughout the global Last Glacial Maximum followed by a rapid deglaciation after 18,000 yr before present.

Here we present an ensemble of transient numerical simulations of the PIS that have been carried out to provide information on its thickness and extents through the MIS 3 and MIS 2. Our aim here is to determine the range of climate conditions that matches the field-derived ice sheet geometries and the timing of local deglaciation, while bracketing the spread in possible ice volumes and sea level contributions originating from uncertainties in the internal parameters and external forcings. The model ensemble makes use of the new higher-order version of the ice sheet model SICOPOLIS forced by combination of present-day atmospheric conditions from the ERA5 reanalysis and outputs from the Paleoclimate Modeling Intercomparison Project (PMIP) and new Community Earth System Model (CESM) experiments. Our results indicate that the regional climate conditions required to reproduce a realistic growth and demise of the PIS through the Late Quaternary are not captured by coarse-resolution global climate models, implying the necessity of high spatial-resolution regional modeling. Our results also suggest that in order to realistically simulate the evolution of the PIS in agreement with geological archives, the MIS3 should have witnessed colder regional temperatures in and around Patagonia than those shown by global climate models for the MIS 2.
Changes in Global Urban Air Quality due to Large Scale Disruptions of Activity
Authors: Drysdale Will , Stapleton Charlotte , Lee James
Published: March 2022

Since 2020, countries around the world have implemented various interventions in response to a global public health crisis. The interventions included restrictions on mobility, promotion of working from home and the limiting of local and international travel. These, along with other behavioural changes from people in response to the crisis affected various sources of air pollution, not least the transport sector. Whilst the method through which these changes were implemented is not something to be repeated, understanding the effects of the changes will help direct policy for further improving air quality. 

 

We analysed NOx, O3 and PM2.5 data from many 100s of air quality monitoring sites in urban areas around the world, and examined 2020 in relation to the previous 5 years. The data were examined alongside mobility metrics to contextualise the magnitude of changes and were viewed through the lens of World Health Organisation guidelines as a metric to link air quality changes with human health. Interestingly, reductions in polluting activities did not lead to wholesale improvements in air quality by all metrics due to the more complex processes involved with tropospheric O3 production.

 
Biogeomorphology from space: Using optical satellite imagery time series for spatially and temporally continuous observation of the interaction of vegetation and hydromorphology along the Naryn River, Kyrgyzstan
Authors: Betz Florian , Lauermann Magdalena , Egger Gregory , Cyffka Bernd
Published: March 2022

The structure and development of river corridors are controlled by an interplay of hydrological, geomorphological and ecological processes over a range of spatial and temporal scales. This is why rivers have been termed biogeomorphological systems by some scholars. Despite the acknowledgement of the relevance of multiple scales, the majority of existing studies on fluvial biogeomorphology focus either on conceptual development or on investigations on the scales of single geomorphic units or study reaches. With this study, we extend the view on biogeomorphology beyond the reach scale using time series of multispectral satellite imagery. We take the Naryn River in Kyrgyzstan as an example for demonstrating our satellite time series approach to biogeomorphological analysis of river corridors. The Naryn is still in a natural state on an entire flow length of more than 600 km with full longitudinal and lateral connectivity. In the central part of the catchment, the Naryn is a highly dynamic braided river system shaped by the annual summer floods of a glacial discharge regime. This makes this river ideal to study large scale biogeomorphological dynamics. In our study, we follow the well-established concept of biogeomorphological succession proposed by Dov Corenblit and his colleagues. We mapped the different succession phases in the field and used the results to derive spectral-temporal indices characterizing the different biogeomorphological succession phases. The normalized difference vegetation index (NDVI) and modified normalized difference water index (MNDWI) have been found to be well suited in the fluvial environment. Monthly time series of these indices derived from the Landsat archive as well as from the more recent Sentinel-2 imagery have now been used to compute statistical trends and changepoints by means of a Bayesian time series decomposition algorithm. The results are then evaluated regarding biogeomorphological succession and disturbance events. The results show that such dense time series of optical satellite imagery are well suited to derive indicators of biogeomorphological interactions on large spatial scale. The temporally continuous nature of this kind of observations allows an observation of processes and an interpretation for instance against the background of the theory of adaptive cycles and panarchy. In conclusion, such satellite time series approach has the potential to give new insights in the structure and functioning of biogeomorphological dynamics of entire river corridors or networks. In particular the recently available Sentinel imagery will allow to observe biogeomorphological processes in a spatially and temporally continuous way at a reasonable spatial resolution. 
Carbon Dioxide Removal and warming reversal in the light of uncertain Earth System processes
Authors: Schleussner Carl-Friedrich , Rogelj Joeri , Frölicher Thomas , MacDougall Andrew , Sanderson Benjamin , Lejeune Quentin
Published: March 2022

Current and projected emissions trends suggest a likely reliance on carbon dioxide removal (CDR) to achieve the long-term temperature goal of the Paris Agreement. Studies using Integrated Assessment Models have considered scenarios limiting global warming to 1.5°C in 2100 that include cumulative net removal of up to ~1000 GtCO2 over the 21st century, although also scenarios deploying substantially less CDR have been considered. Large CDR deployment beyond achieving net zero emissions is often assumed to achieve a Global Mean Temperature (GMT) decline after peak warming of several tenths of a degree by the end of the century. The feasibility of achieving CDR on such a large scale has been strongly contested for environmental, technological, geophysical, economic, institutional or socio-cultural reasons. Beyond these considerations, it is important to assess the possible realisation of a GMT decline in the context of  uncertainties in the Earth System response.

Here we attempt to review and compare these various sources of uncertainty. Some relevant Earth System feedbacks  are not represented in climate models or only in a limited manner, such as carbon release from permafrost melting, wetlands and wildfires, which could release ~100 GtCO2 over the 21st century even in stringent mitigation scenarios, but there is low confidence around this number. Another source of uncertainty is the Zero Emissions Commitment, which quantifies how much global warming would occur after global CO2 emissions reach net zero. Its best estimate over 50 years is close to zero, but uncertainties were quantified to be as high as +/-0.3°C for cumulative emissions of 1000 PgC and uncertainties remain on the potential for warming on multi century timescales. Given this, additional post net-zero warming countering CDR induced cooling cannot be ruled out. Furthermore, it is not clear whether the TCRE assessed for increasing CO2 emissions would remain the same once we reach net-negative emissions. In light of these various sources of uncertainty we argue that a broader perspective on CDR and future GMT evolution beyond net zero is advisable. Acknowledging the uncertain efficacy of CDR-induced GMT decrease is important for comprehensive risk assessments and reflections on scenario design.
Fluid flow properties of carbonate rocks under simulated in-situ conditions: Implications for geothermal reservoir quality
Authors: Ahrens Benedikt , Lippert Kevin , Nehler Mathias
Published: March 2022

Medium-depth and deep geothermal systems hosted in carbonate rocks are amongst the most promising geothermal resources in the world due to their favorable geological and stress- and temperature-sensitive petrophysical heterogeneity. In general, structural heterogeneities such as natural fractures, karstifications, cavities or entire fracture networks mainly dominate geothermal fluid flows and storages and, thus, dictate the reservoir quality. However, especially for carbonate reservoirs, it is even more complex, as a profound understanding of the links between diagenetic processes, facies, deformations, porosities, and fluid flow properties is essential to estimate the distribution of reservoir quality. This assessment is further complicated by the spatially and temporally varying pressure and temperature conditions (e.g., recharge and discharge of geothermal systems).

In the wake of Bavaria’s (southern Germany) success story in exploiting the geothermal systems hosted in deep carbonates, there are extensive investigations to determine the geothermal potential of Devonian carbonates in North Rhine-Westphalia (western Germany). The geothermal potential of these Devonian carbonates strongly depends upon how and to what extent the tectonically influenced burial history and diagenetic processes have modified the pore network and promoted heterogeneities such as fractures and karstifications. In our triaxial experiments, we examined the influence of in-situ stress and temperature and their histories as well as the influence of brittle faulting on porosities and hydraulic properties of different Devonian carbonate rocks. From analogue outcrops limestone, dolomitic limestone, dolostone, and fractured carbonates were sampled and petrophysically investigated. The stresses simulated covered both hydrostatic and triaxial states. Furthermore, the influence of elevated temperature and stress on the hydraulic properties of samples triaxially compressed at effective confining pressures was also studied systematically. Our results show that the interplay of temperature and stress state, and their histories, are fundamental for the evolution of hydraulic properties in the reservoir. Depending on the rock’s mineralogy, the mineral expansion caused by the increased temperature can surpass the effect of microcracking due to heating, resulting in a significant decrease in hydraulic properties. Our results were supplemented by micro-CT images of the microstructure of the samples before and after triaxial testing. It is shown that the interaction of temperature and stress is fundamental for the assessment of the geothermal potential of both intact and fractured carbonate reservoirs.
Determination of parameters characteristic of dynamic weakening mechanisms during coseismic slip
Authors: Cornelio Chiara , Spagnuolo Elena , Nielsen Stefan , Aretusini Stefano , Passelègue Francois , Violay Marie , Cocco Massimo , Di Toro Giulio
Published: March 2022

While sliding at seismic slip-rates of ca. 1 m/s, a natural fault undergoes an abrupt decrease of its strength called enhanced dynamic weakening. Asperity-scale (<< mm) processes related to flash heating & weakening and meso-scale (mm-cm) processes involving shear across the bulk slipping zone related to frictional melting or viscous flow of minerals, have been invoked to explain pronounced velocity-dependent weakening. Here we present a compilation of ca. 100 experiments performed with two rotary shear apparatuses, i.e. SHIVA installed in INGV (Rome, Italy) and HVR installed, at the time of experiments, in Kyoto University (Japan). Cohesive rock cylinders of basalt, gabbro, tonalite, granite and calcitic marble were sheared under a range of effective normal stresses (sn=5-40 MPa), target slip-rates (Vt=0.1-6.5 m/s) and fluid pressures (from room humidity conditions RH or Pf=0, to Pf =15 MPa). We fit the measured shear stress evolution with slip with two dynamic weakening mechanisms models, which include, depending on rock type: (1) flash heating and bulk melting (granitoid, gabbro and basalt), (2) flash heating and diffusion creep (calcitic marble), (3) flash heating and dislocation creep (calcitic marble). We provide a set of optimized parameters, specific for each mechanism, that control the dynamic weakening.

Lastly, the modelling procedure allow us to estimate the slip-switch distance d0, i.e. the slip necessary for the complete transition from the asperity-scale to bulk slipping zone dynamic weakening mechanism. Our analysis shows that (1) the d0 decreases with increasing effective normal stress acting on the fault and, (2) for the same type of transition between dynamic weakening mechanisms (e.g., from flash heating to bulk melt lubrication) the d0 is a function of rock composition. The decrease of d0 with normal stress indicates that during earthquakes, bulk mechanisms dominate over asperity scale weakening mechanisms with increasing crustal depths. This study provides constitutive law parameters to be included in physically- and geologically-based dynamic earthquake rupture simulations.
Cutting peatland CO2 emissions with rewetting measures
Authors: Boonman Jim , Hefting Mariet , van Huissteden Corine , van den Berg Merit , van Huissteden Jakobus , Erkens Gilles , Melman Roel , van der Velde Ype
Published: March 2022

Peat decomposition in managed peatlands is responsible for a decrease of 0.52 GtC yr-1 in global carbon stock and is strongly linked to drainage, which increases the oxygen availability in the soil. Microbial aerobic decomposition is responsible for the bulk of the net CO2 emission from the soil. This decomposition could be reduced by rewetting efforts or minimizing drainage, but the effects of rewetting on microbial respiration rate are largely unknown. Our research aims to assess the effects of rewetting measures on soil wetness, soil temperatures and CO2 emissions by field data collection and simulations of peatland parcels under dairy farming. Here we present the results for two dairy farming peatlands where subsoil irrigation and drainage (SSI), which aims to increase summer groundwater tables. At both dairy farms parcels with rewetting measures were tested against a control situation for the year 2020. Furthermore, we introduce a process-based methodology to estimate potential aerobic microbial respiration rate as measure for peat decomposition in managed peatlands, based on potential respiration rate curves for soil temperature and water filled pore space (WFPS). This methodology enables us to quantify effects of rewetting under different weather conditions, water management strategies (raising ditch water levels and SSI) and hydrological settings (i.e. seepage). We present the effects of the water management strategies on CO2 emissions, groundwater table height and soil moisture and discuss to what extent we can rely on commonly used groundwater table-based proxies to estimate peat decomposition. Towards improved understanding of biophysical soil processes and peatland management!
Paleomagnetic data from Siberian Ediacaran rocks (Yenisei Ridge and Olenek Uplift)
Authors: Vinogradov Evgeny , Metelkin Dmitriy , Zakharov Sergey , Abashev Victor , Pakhomova Kristina , Eliseev Andrey
Published: March 2022

Paleomagnetic results obtained from rocks of Ediacaran age in several localities in Siberia display co-existence of two magnetization components, one shallowly component and the other one is steeply inclined. Both components pass criteria for a primary magnetization. The conventional interpretation of paleomagnetic results in such cases have been rejected as dynamically implausible. In search of the reasons for the irregular behavior of the geomagnetic field in the Ediacaran, the study compares the key Ediacaran sections of the Yenisei Ridge and the Olenek Uplift, which are close in age.

The first paleomagnetic data for the Vorogovka Group were obtained in the northwest of the Yenisei Ridge. Age of deposits, according to different authors, from Cryogenian to Ediacaran. However, recent data indicate that the age of sedimentation within the Vorogovka basin is less than 585 million years. In the southwestern margin of the Siberian platform, the Taseeva Group is of considerable interest for paleomagnetic studies. New data on the age make it possible to significantly narrow the formation interval of the series to the Late Ediacaran, and also to refine the paleomagnetic pole calculated for the upper and lower formations of the Taseeva Group. In the Vorogovka and Taseeva groups, the shallowly inclined component of magnetization is more often present, while the steeply inclined component is less common.

Over the past several years, we have carried out paleomagnetic studies of the Precambrian rocks of the Olenek Uplift, including the Late Ediacaran Maastakh and Khatyspyt formations, as well as intrusions of the Tas-Yuryakh volcanic complex that break through them. In both sedimentary and igneous rocks of the Olenek Uplift, only a steeply inclined component of magnetization is present.

The results of the studies of paleointensity in basalts of the Tas-Yuryakh volcanic complex indicate an ultra-low intensity of the Earth's magnetic field at the end of the Ediacaran. These results confirm that the explanation for the disparate paleomagnetic data for the Ediacaran period must be sought in the behavior of the geomagnetic field, and not in tectonic reasons.

This work was financially supported by the Russian Science Foundation grant no. 21-17-00052.
Reservoir siltation mapping uncertainties – experiences from South Africa
Authors: Baade Jussi , Zoller Kevin , van Zyl Wilhelm , Cawthra Hayley
Published: March 2022

Mapping reservoir siltation is an often-used method for assessing sediment yield and soil erosion from catchments. An advantage of this approach is that measurements can potentially provide mean values that represent timeframes of several decades and thus overcome the bias induced by climate fluctuations, especially in semi-arid and arid regions. Furthermore, reservoir siltation mapping can be performed repeatedly, and thus repeated sediment yield trends over time can be derived. There are several studies that report sediment yield estimates based on reservoir siltation surveys, however, information on the uncertainties involved in these measurements is not frequently reported.

In October 2019 and March 2020, we conducted reservoir siltation surveys of eight mid-size (~ 10 mio m³ water storage capacity), filled and dried-out reservoirs in South Africa. The water-filled reservoirs were surveyed using single beam, single frequency echosounders mounted to a boat. The dried-out reservoirs were surveyed using differential GNSS and a Terrestrial Laser-Scanner (TLS) with a scanning range of up to 1 km deployed at multiple scanning positions.

In this contribution we present survey results, report on the issues encountered during the surveys and the uncertainties observed in the results. For the water-filled reservoirs we derived depth measurement uncertainties from the survey leg intersection points. Here, the mean measurement error is in the order of 0.1 m (p= 0.05). When this uncertainty of the volume estimation is applied to the water storage capacity of the dams, the resulting uncertainties are inthe order of a few percent, only. However, if this volume estimation uncertainty refers to the volume of the sediment at the bottom of the reservoirs, the relative error is can be in the order of a few ten percent. From this we conclude, that depending on the sediment inflow, it may take several decades before a repeated survey can establish a meaningful trend in sediment yield from the catchment beyond the measurement uncertainties involved.
Characterizing soil-plant interactions under heterogeneous micro-irrigated citrus orchards
Authors: Vanella Daniela , Longo-Minnolo Giuseppe , Ramírez-Cuesta Juan Miguel , Longo Domenico , D'Emilio Alessandro , Consoli Simona
Published: March 2022

The increased water demand from the irrigated agriculture sector calls for the introduction of more efficient water saving strategies in order to maintain sustainable crop production. This need is particularly urgent in Mediterranean climate areas, already deeply affected by water scarcity and soil depletion issues. In this context, the use of advanced near surface geophysics monitoring techniques can help to characterize the temporal and spatial soil physics dynamics and the related soil moisture processes active at the root-zone level aiming at optimizing the irrigation management.

In this study, the electrical resistivity imaging (ERI) technique was applied for characterizing the mass exchange mechanisms acting within the soil-plant system of heterogeneous micro-irrigated orchards. In particular, repeated ERI surveys were carried out in a citrus orchard (Citrus sinensis (L.) Osbeck), located in Eastern Sicily, southern Italy, characterized by the presence of crop heterogeneity features within the same plant framework, both in terms of variety and age (i.e. 3-year old Tarocco Ippolito and 8 year-old Tarocco Nucellare Scirè, respectively).

The time-lapse ERI monitoring has permitted to identify specific wetting fronts and root water uptake (RWU) patterns effective in the soil / root system during dynamic condition (i.e. an irrigation cycle), mostly affected by the complex nonlinear interactions (i.e., soil evaporation, RWU and soil water redistribution) operating under crop heterogeneous conditions. Moreover, the use of soil moisture sensors installed in situ has permitted to identify a clear relationship between the changes in the soil water content observed in the field and the soil electrical resistivity (ER) characteristics with reference to the different types of analysed tree crops (with overall R2 value of 0.63). Specifically, it has been observed that the soil evaporative process, represented by an increasing of ER values, was greater in the younger citrus trees due to their lower vegetation groundcover and roots development. While, the greater soil moisture changes (resulting in greater ER decreasing patterns) occurred for the mature tree crops, characterized by higher root biomass, because its initial soil water condition was lower in comparison to the young tree crops.
Crustal architecture under the NE Brazil syn-rift basins from receiver functions: Evidence of deep magmatic processes.
Authors: Julià Jordi , Döring Miro , Barbosa Thabita
Published: March 2022

NE Brazil is scarred by a number of aborted rift basins that developed from the same extensional stresses that lead to the opening of the South Atlantic. Extension started in Late Jurassic times, with the formation of an AfroBrazilian Depression south of the Patos Lineament, and continued through the Early Berriasian along two NS trending axes of deformation: Recôncavo-Tucano-Jatobá (RTJ) and Gabon-Sergipe-Alagoas (GSA). In the Late Berriasian - Early Barremian, rifting jumped North of the Pernambuco Lineament to progress along the NE-SW trending Cariri-Potiguar (CP) axis. In the Late Barremian, approximately coinciding with the opening of the Equatorial Atlantic, rifting aborted along the RTJ and CP axes and continued along the GBA trend eventually resulting in continental break-up. Extension-related magmatic activity seems to have been restricted to break-up along the marginal basins, although dyke swarms bordering the Potiguar basin (Rio Ceará-Mirim) seem to be associated to early extension stages in NE Brazil and three subparallel dolerite dykes, with K-Ar dates of 105±9 Ma, were inferred indirectly from aeromagnetic and outcrop data East of the RTJ axis. Aiming at better understanding the structure and evolution of the syn-rift basins of NE Brazil, a total of 20 seismic stations were deployed between October 2018 and January 2021 along the CP and RTJ trends. The deployment, funded by the national oil company Petrobras, included both broadband and short-period stations borrowed from the Pool de Equipamentos Geofísicos do Brasil. These stations complemented a number of permanent broadband stations belonging to the Rede Sismográfica do Brasil. Receiver functions were obtained for each of the seismic stations from teleseismic P-wave recordings and S-wave velocity models were developed from their joint inversion with dispersion velocities from an independent tomographic study. In the RTJ basins, our results show that the crust is about 41 km thick and displays a thick (5-8 km) layer of fast-velocity material (> 4.0 km/s) at its bottom; in the Potiguar basin, our results show a thinner crust of about 30-35 km underlain by an anomalously slow (4.3-4.4 km/s) uppermost mantle. We argue that those anomalous layers are the result of syn-rift and/or post-rift magmatic intrusions, which would have had the effect of increasing velocity at lower crustal levels under the RTJ basins and decreasing velocity at uppermost mantle depths under the Potiguar basin. If correct, ou interpretation would imply that, in spite of an overall lack of evidence at shallow levels, deep magmatic processes have played a role in the formation and evolution of the syn-rift basins of NE Brazil.