bluuebunny/crossref_metadata_2025 huggingface dataset:
On the recoverability of geomechanical model complexities from surface deformation data above the Groningen gas field
Authors: Wouters Marius , Kim Samantha S. R. , Vossepoel Femke C. , Govers Rob
Published: March 2022

Since the start of production in 1968 in the Groningen gas field (Netherlands) considerable land subsidence (>30 cm) has occurred above the field. The PS-InSAR technique provides surface deformation data with a high spatial and temporal resolution. However, using this data to obtain a detailed solution for the reservoir compaction distribution is not trivial because of: (1) uncertainties in the data (e.g., atmospheric noise), (2) soil deformation (e.g., clay shrinkage and peat oxidation), and (3) non-uniqueness of different reservoir compaction distributions leading to identical surface signals. This study is part of the DeepNL/Subsidence project, where we aim to identify the drivers of subsidence in the Groningen field by assimilating geodetic time series in geomechanical models of the subsurface, to disentangle the signals from deep (reservoir and overburden) and shallow (soils) drivers. In this study we perform a sensitivity analysis to investigate the level of complexity that can be resolved for the reservoir geometry, for the reservoir compaction, and for the mechanical properties of the reservoir and overburden.

We employ a semi-analytical mechanical model for the Groningen subsurface using the PSGRN/PSCMP code by Wang et al. (2006). The model geometry is based on the geological model constructed by the producer (NAM, 2020). We simplify the geology by using lateral uniform material properties and we construct multiple versions of the mechanical model with different levels of complexity (of reservoir geometry, reservoir compaction and mechanical properties). The synthetic surface deformation results produced by the models are used in an inversion to investigate whether the applied complexities can be recovered from inverting the surface signal. Information theory analysis is used to determine how much of the originally applied information is recovered by the inversion and to define a threshold complexity. Model versions that are more complex than the threshold complexity lead to non-uniqueness inhibiting a robust solution. We finally analyse the spatial characteristics of the surface deformation results, to determine whether the InSAR data uncertainty warrants an additional lowering of the complexity threshold.

 

NAM (2020). Petrel geological model of the Groningen gas field, the Netherlands. Open access through EPOS-NL. Yoda data publication platform Utrecht University.

Wang, R., Lorenzo Martín, F., Roth, F. (2006): PSGRN/PSCMP - a new code for calculating co- and post-seismic deformation, geoid and gravity changes based on the viscoelastic-gravitational dislocation theory. Computers and Geosciences, 32, 4, 527-541. https://doi.org/10.1016/j.cageo.2005.08.006
Supercomputing of large earthquakes
Authors: Gabriel Alice-Agnes
Published: March 2022

Earth modeling is extraordinarily complex - and when the earth quakes, it’s no different. Earthquakes are highly non-linear and multiscale processes fracturing the Earth’s crust and emanating potentially destructive seismic waves. While computational seismology has been a pioneering field for high-performance computing, the multitude of scales and multi-physics character of earthquake source processes remain difficult to constrain.

Earthquake science is increasingly data-rich, which opens up new pathways to synergistically integrate seismological, geodetic, tectonic and experimental analysis in multi-physics forward modeling. Using a physics-based description of earthquakes, interdisciplinary earthquake observations,  modern numerical methods and hardware specific optimisation shed light on the dynamics, severity and cascading hazards of earthquake behaviour. An unparalleled degree of realism is enabled by exploiting high-performance computing.

In this lecture, I will demonstrate the potential of Solid Earth community software for performing data-integrated, parsimonial scenarios of recent powerful multi-fault earthquake cascades, 3D fully-coupled Earth and ocean models of tsunami generated during earthquakes as well as cycles of earthquake and aseismic slip using petascale supercomputers. The inclusion of probabilistic and Bayesian frameworks, geometric transformations and diffuse interface approaches are future directions I will discuss for exploiting the expected exascale computing infrastructure.
The hydrodynamic potential of eroding arctic permafrost coasts: fractionation of permafrost parent material in the Canadian Arctic to determine its fate in the marine system
Authors: van Crimpen Fleur , Madaj Lina , Whalen Dustin , Tesi Tommaso , Vonk Jorien
Published: March 2022

The Canadian Beaufort Sea coastline consists of permafrost, permanently frozen soils, that store large amounts of organic carbon (OC). Rising temperatures in the Arctic will lead to thaw of these permafrost soils as well as enhanced coastal erosion. The trajectory of thawing coastal carbon upon thaw will determine the degree of breakdown and greenhouse gas emission, impacting climate warming. However, we still have a poor understanding of the marine fate of sediments and OC from eroding arctic coastlines.

In order to obtain more insight into the fate of the eroding material, we will use hydrodynamic fractionation on a variety of actively eroding coastal cliffs (parent material). Hydrodynamic fractionation accounts for the sediment sorting of particles when exposed to different energy conditions such as waves. With this technique we will fractionate based on density and grainsize to mimic the route in the marine system. Current estimates of sediment and OC input from arctic coastal erosion are only based on bulk measurements.

Samples were collected from eight sites (n=5 at each site) with a wide spatial and geological variation across the Canadian Beaufort Sea. These sites range from peaty and flat islands to muddy slumps and sandy locations. For all sites, parent material was collected onshore, fractionated and separated in five fractions based on density (cut-off 1.8 g/mL) and grainsize (cut-offs 38, 63, and 200mm). All fractions will be analysed for geochemical properties (total OC, total nitrogen, δ13C, and D14C, biomarkers and lipids) in order to determine the quantity and quality of the organic matter. Distribution of sediment fractions based on weight shows large variability between sites (e.g. low density fraction between 2-13% and high density between 9-50% with grainsize 63-200mm) as well as within sites, depending on the characteristics of the coast. Using the spatial variability of these fractions in combination with coastal characteristics assessed with GIS techniques we will attempt to upscale for the Canadian Beaufort Coast. This will hopefully improve our insights on the type and composition of parent material which is released into the marine system as a source of carbon.
Prediction of evapotranspiration using a nonlinear local approximation approach
Authors: Vamsi Krishna Gunturu , Jothiprakash Vinayakam , Sivakumar Bellie
Published: March 2022

Evapotranspiration is a key process in the water cycle. Evapotranspiration is influenced by several hydro-meteorological variables in complex and nonlinear ways and, therefore, its estimation is often very challenging. This study employs a chaotic time series approach to predict evapotranspiration. Measured monthly evapotranspiration data over a period of 40 years (1976–2015) from the Rietholzbach monitoring station in Switzerland are analysed. The nonlinear local approximation prediction method, which uses nearest neighbours, is employed. The method involves the following steps: (1) Phase-space reconstruction of a single-variable time series in a multi-dimensional phase space using delay embedding; (2) Identification of the nearest reconstructed vectors using Euclidean distance; and (3) Prediction of the future value based on the evolution of the nearest neighbours in the phase-space. The phase-space reconstruction is done with embedding dimension (m) from 1 to 10, and nearest neighbours (k) varying from 1 to 300 are used for prediction. Out of the 480 monthly evapotranspiration values available, the first 320 values are used for phase-space reconstruction and prediction, and the remaining 160 values are used for checking the prediction accuracy. The performance of the prediction method is evaluated using correlation coefficient and root mean square error. The results generally indicate very good predictions. The prediction accuracy generally increases with an increase in the embedding dimension up to a certain point and then somewhat saturates beyond that point. The best predictions are achieved when the embedding dimension is five and the number of neighbours is 10, with a correlation coefficient value of 0.86 and root mean square error value of 14.64 mm. The low embedding dimension and small number of neighbours yielding the best predictions suggest that the dynamics of monthly evapotranspiration in the Rietholzbach station exhibit chaotic behaviour dominated by five governing variables. The optimal embedding dimension value obtained from the prediction method also matches with the optimal embedding dimension estimated using the False Nearest Neighbour (FNN) algorithm, which is a dimensionality-based approach. The results from this study have important implications for modelling and prediction of evapotranspiration.

Keywords:

Evapotranspiration, Chaos, Local approximation prediction, Phase space reconstruction, False nearest neighbour algorithm
Processes controlling the transportation of microplastics in agricultural soils
Authors: Severe Emilee , Surridge Ben , Quinton John
Published: March 2022

Every year 12.5 million tons of plastic are used in agricultural production across the globe with plastic films accounting for 75% of this plastic. Once added to the soil, removing agricultural plastic is challenging as exposure to sunlight and other environmental elements fragment the plastics into macro- and microscopic pieces. In addition to this direct input, agricultural soils accumulate microplastics from several other sources e.g., biosoilds input, runoff from roads and atmospheric deposition. Soils are usually thought of as sinks for plastic waste but growing literature suggests mismanaged agricultural soils could be significant sources of plastics to aquatic and other terrestrial environments. In this study, we investigated the process of microplastic movement in response to rainfall and overland flow. We compared the movement of two types of plastic (linear low-density polyethylene and acrylic) in two size fractions with sand particles in rainfall simulation experiments. We examine the extent to which plastic particles are preferentially eroded compared to fine sand particles, alongside the relative importance of particle size and polymer type for controlling the erosion of plastics from soil.
Deformation-facilitated melting of plagioclase
Authors: Incel Sarah , Baisset Marie , Labrousse Loic , Schubnel Alexandre
Published: March 2022

Geological processes involving deformation and/or reactions are highly influenced by the rock grain size, especially if diffusion-controlled processes take place such as long-range metamorphic reactions and diffusion creep. Although many processes, inducing grain-size reduction, are documented and understood at relatively high stresses and low temperatures (e.g., cataclasis) as well as at lower stress and higher temperature conditions (e.g., bulging, subgrain rotation), deformation twinning, a plastic deformation mechanism active in various minerals at lower temperatures, has been neglected as cause for grain-size reduction so far. We conducted experiments on natural plagioclase-bearing aggregates at 2.5 to 3 GPa confining pressure and temperatures of 720 to 950 °C using two different deformation apparatus, a DDIA and a Griggs press, as well as a piston-cylinder apparatus. Regardless of the apparatus type, we observe the breakdown of plagioclase into an eclogite-facies paragenesis, which is associated with partial melting in the high pressure, high temperature domain of the eclogite facies. In contrast to the sample that experienced hydrostatic conditions in the piston-cylinder press, the deformed samples reveal melt patches inside of several plagioclase grains. These patches coincide with the occurrence of deformation twins in plagioclase that formed due to differential stress. The ability of plagioclase to form deformation twins and their exploitation for melt initiation significantly lowers the effective grain size of plagioclase-rich rocks and thus impacts their reactivity and deformation behavior.
Analysis and Modelling of 2009-2013 Unrest Episodes at Campi Flegrei Caldera
Authors: Castaldo Raffaele , Solaro Giuseppe , Tizzani Pietro
Published: March 2022

Geodetic modelling is a valuable tool to infer volume and geometry of volcanic source system; it represents a key procedure for detecting and characterizing unrest and eruption episodes. In this study, we analyse the 2009–2013 uplift phenomenon at Campi Flegrei (CF) caldera in terms of spatial and temporal variations of the stress/strain field due to the effect of the retrieved inflating source. We start by performing a 3D stationary finite element (FE) modelling of geodetic datasets to retrieve the geometry and location of the deformation source. The geometry of FE domain takes into account both the topography and the bathymetry of the whole caldera. For what concern the definition of domain elastic parameters, we take into account the Vp/Vs distribution from seismic tomography. We optimize our model parameters by exploiting two different geodetic datasets: the GPS data and DInSAR measurements. The modelling results suggest that the best-fit source is a three-axis oblate spheroid ~3 km deep, similar to a sill-like body. Furthermore, in order to verify the reliability of the geometry model results, we calculate the Total Horizontal Derivative (THD) of the vertical velocity component and compare it with those performed with the DInSAR measurements. Subsequently, starting from the same FE modelling domain, we explore a 3D time-dependent FE model, comparing the spatial and temporal distribution of the shear stress and volumetric strain with the seismic swarms beneath the caldera. Finally, We found that low values of shear stress are observed corresponding with the shallow hydrothermal system where low-magnitude earthquakes occur, whereas high values of shear stress are found at depths of about 3 km, where high-magnitude earthquakes nucleate.
Response of the traveling planetary waves at low latitude middle atmosphere during September 2019 minor sudden stratospheric warming
Authors: Mitra Gourav , Guharay Amitava , Batista Paulo , Buriti Ricardo
Published: March 2022

Planetary wave (PW) associated dynamical variability in the equatorial and extratropical middle atmosphere during the September 2019 Southern hemisphere minor sudden stratospheric warming (SSW) is investigated utilizing meteor radar wind observations from São João do Cariri (7.4°S, 36.5°W) and Cachoeira Paulista (22.7°S, 45°W) and reanalysis data. Signature of the mesospheric warming in conjunction with the stratospheric cooling is found at low latitudes. The strong westerly wind at low latitudes decelerates notably near 65 km at the onset of the warming episode, although no wind reversal is observed. The wind spectra reveal a prevalent quasi-16-day wave (Q16DW) prior to the SSW and existence of a quasi-6-day wave (Q6DW) after the warming event. Possible existence of barotropic/baroclinic instability in the low and mid latitude middle atmosphere may be responsible for exciting the Q6DW. The traveling PW is primarily found to travel westward corresponding to zonal wavenumber 1 and 2. Furthermore, significant latitudinal mixing of airmass between the tropics and high latitudes is evident in the potential vorticity map. The Eliassen-Palm flux diagnosis shows the propagation of the Q6DW and Q16DW from mid to low latitudes during the warming event.
Quantifying SO2 emissions from the 2021 eruption of Fagradalsfjall, Iceland, with TROPOMI and PlumeTraj
Authors: Esse Ben , Burton Mike , Hayer Catherine , Barsotti Sara , Pfeffer Melissa
Published: March 2022

Effusive eruptions are a significant source of volcanic volatile species, injecting various reactive and climate altering products into the atmosphere, while low-level emissions can be hazardous to human health due to the degradation of local or regional air quality. Quantification of the flux and composition of these emissions also offers an insight into the magmatic processes driving the eruption. These factors mean that gas flux measurements are a key monitoring tool for managing the response to such eruptions. The usual target species for gas flux measurements is sulphur dioxide (SO2) due to its high concentration in volcanic emissions but low ambient concentration, and its ability to be measured with UV and IR spectroscopy from both ground and space.

Fagradalsfjall volcano, Iceland, underwent an effusive eruption between March – September 2021, emitting over 100 million m3 of lava and producing significant SO2 emissions. The eruption progressed through several distinct phases in eruptive style, with different surface activity and gas emission behaviour for each. Satellite instruments have not traditionally been used for monitoring emissions from effusive eruptions such as this, as they often lack the spatial or temporal resolution to detect and quantify low-level effusive emissions. However, the launch of ESA’s Sentinel-5P, carrying the TROPOMI instrument, in October 2017 opened the door for such measurements, offering a step change in sensitivity to tropospheric emissions over previous missions.

Here, we will present measurements of altitude- and time-resolved SO2 fluxes from Fagradalsfjall by combining TROPOMI observations with a back-trajectory analysis toolkit called PlumeTraj. We compare the emissions with other geophysical monitoring streams throughout the eruption and explore changes across the different phases of the eruption. This will demonstrate the ability of TROPOMI and PlumeTraj for quantifying intra-day, low-level SO2 emissions and highlight the potential insight these measurements can provide for future effusive eruptions.
Airblast caused by large slope collapses
Authors: Penna Ivanna , Hermanns Reginald , Nicolet Pierrick , Morken Odd Andre , Dehls John , Gupta Vikram , Jaboyedoff Michel
Published: March 2022

The sudden impact of a large slope collapse on the ground can cause a high degree of comminution of rocks and trigger an extreme rush of air loaded with particles, called an airblast. The airblast can expand the destructive capacity of a large slope collapse far beyond the run-out of the rock mass. The first airblast event documented in detail occurred in 1881 as consequence of a large collapse at Elm in the Unthertal valley (Switzerland). People being blown over by the air pressure wave were reported. In 2015, two rock avalanche related airblasts occurred in the Himalayas. In March 2015, an airblast in Yumthang valley (Sikkim, India) knocked down and snapped trees 1.4 km away from the impact zone of a rock avalanche. In April 2015, an avalanche triggered by the Gorkha earthquake induced a violent airblast that caused several casualties in Langtang valley. The destruction of stone and wooden houses can be observed in video footage. The damage on trees can be traced over a distance of 3.5 km and 400 m above the impact zone of the avalanche on the opposite slope. The most recent documented event occurred in February 2021 in Chamoli (India), where the flattened forest extends over 20 hectares.

This work presents a back analysis of the April 2015 airblast in the Sikkim Himalayas (India) and compares it with several other airblasts documented around the world. We review the conditions a large slope collapse should meet to cause a significant airblast. We also formulate an equation that links the potential energy of collapses having airborne trajectory to the extent of the related airblast.
More frequent dry and wet spells increase stochastic microbial community assembly in grassland soils
Authors: Li Lingjuan , Beemster Gerrit , Reynaert Simon , Nijs Ivan , Laukens Kris , Asard Han , Vinduskova Olga , Verbruggen Erik
Published: March 2022

Climate change is leading to an increased frequency and severity of alternating wet and dry spells. These fluctuations affect soil water availability and other soil properties which are crucial drivers of soil microbial communities. While soil microbial communities have a reasonable capacity to recover once a drought seizes, the expected alternation of strongly opposing regimes can pose a particular challenge in terms of their capacity to adapt. Here, we set up experimental grassland mesocosms where precipitation frequency was adjusted along a gradient while holding total precipitation constant. The gradients varied the duration of wet and dry "spells" from 1 to 60 days during a total of 120 days, where we hypothesized that especially intermediate durations would lead to stochastic community assembly due to frequent alternation of opposing environmental regimes. We examined bacterial and fungal community composition, diversity, co-occurrence patterns and assembly mechanisms across these different precipitation frequencies. Our results show that 1) intermediate frequencies of wet and dry spells increased the stochasticity of microbial community assembly whereas microbial communities at low and high regime persistence were subject to more deterministic assembly, and 2) more persistent precipitation regimes (> 6 days duration) reduced the fungal diversity and network connectivity but had a less strong effect on bacterial communities. Collectively, these findings indicate that recurring wet and dry events lead to a less predictable and connected soil microbial community. This study provides new insight into the likely mechanisms through which precipitation frequencies alter soil microbial communities and their predictability.
Modelling nitric acid uptake by mineral dust using parameterizations of different complexity
Authors: Soussé Villa Rubén , Jorba Casellas Oriol , Pérez García-Pando Carlos
Published: March 2022

Mineral dust is amongst the largest contributors to the global aerosol mass load and dominates climate effects over large areas of the Earth. Dust undergoes heterogeneous chemical reactions during transport that increase its hygroscopicity, while altering its optical properties, and the associated radiative forcing. The rates of heterogeneous chemical reactions on the dust surface that form coatings of sulfate, nitrate, chloride, or organics depend strongly on the dust mineralogical composition. For example, the uptake of sulfur dioxide by calcite exceeds by at least an order of magnitude uptake by quartz, feldspar and hematite. Dust composition also affects the partitioning of semi-volatile inorganic compounds, altering their burden and radiative forcing.

In this work, we perform an analysis of the treatment of nitric acid heterogeneous chemistry on mineral dust in atmospheric models. We have implemented aerosol nitrate formation on coarse particles in the Multiscale Online Nonhydrostatic AtmospheRe CHemistry model (MONARCH) and we have performed sensitivity experiments with parametrizations of varying complexity. First-order uptake reactions with/without dependence on relative humidity are compared against approaches based on thermodynamic equilibrium assumptions, that range from just considering the effect of dust mineralogy upon aerosol pH to including the formation of subproducts from the gas-mineral interaction. The sensitivity to the mineral dust treatment (i.e., minerological composition) in each approach is discussed. The different implementations are evaluated against observations and compared with literature results.

Our preliminary findings highlight the important role that mineralogy plays in mineral dust chemistry, and the relevance that thermodynamic assumptions have when simulating the complex evolution of mineral dust in the atmosphere. This work aims to set a benchmark for future sensitivity studies to factors affecting dust heterogeneous chemistry, such as the explicit representation of regional variations in the mineralogical composition of dust.
Gravity data acquisition and validation of the interferometric meaurement concept with the transportable absolute Quantum Gravimeter QG-1
Authors: Herr Waldemar , Heine Nina , Rasel Ernst M. , Müller Jürgen , Timmen Ludger
Published: March 2022

The transportable Quantum Gravimeter QG-1 derives the local gravity value from the interferometric signal of magnetically collimated Bose-Einstein condensates (BECs) released into free-fall and detected by absorption imaging. The objective of the device is to determine the local gravity value with an uncertainty < 3 nm/s2. The projected gain in accuracy in contrast to cold atoms is facilitated by the minimised initial velocity and expansion rate of the BEC.

In this contribution we describe our transportable setup, the status of implementation of first interferometric studies and give an evaluation of preliminary gravity data recorded with the Quantum Gravimeter QG-1, showing the operability of key functionalities of the device and the validity of
the concept. We indicate next steps to increase the instrument’s sensitivity and to verify the measurement’s level of uncertainty.

The research is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2123
QuantumFrontiers – 390837967 and under Project-ID 434617780 – SFB 1464 TerraQ - Relativistic and Quantum-based Geodesy.
Space-time groundwater level distribution estimation in a complex system of aquifers 
Authors: Varouchakis Emmanouil , Trichakis Ioannis , Karatzas George
Published: March 2022

A geostatistical analysis based on a machine learning method was conducted to generate reliable spatial maps of groundwater level variability and to identify groundwater level patterns over the island of Crete, Greece. Geostatistics plays an important role in model-related data analysis and preparation, but has specific limitations when the aquifer system is inhomogeneous. Self-Organizing Maps can be applied to identify locally similar input data and then by means of Ordinary Kriging to estimate the spatial distribution of groundwater level. The proposed methodology was tested on a large dataset of groundwater level data in a complex hydrogeological district, and the results were significantly improved if compared to the use of classical geostatistical approaches.

This work was developed under the scope of the InTheMED project. InTheMED is part of the PRIMA programme supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 1923.
Magnetosheath jets at the magnetopause: reconnection onset conditions
Authors: LaMoury Adrian , Hietala Heli , Eastwood Jonathan , Vuorinen Laura , Plaschke Ferdinand
Published: March 2022

Magnetosheath jets are localised pulses of high dynamic pressure plasma observed in Earth’s magnetosheath. They are believed to form from the interaction between the solar wind and ripples in Earth’s collisionless bow shock, before propagating into the turbulent magnetosheath. Upon impacting the magnetopause, jets can influence magnetospheric dynamics. In particular, previous studies have suggested that, by virtue of their internal magnetic field orientations, jet impacts may be able to trigger local magnetic reconnection at the magnetopause. This is most notable during traditionally unfavourable solar wind conditions, such as intervals of northward interplanetary magnetic field. This idea has been supported by a small number of case studies and simulations. We present a large statistical study into the properties of jets near the magnetopause. We examine the components of the magnetic reconnection onset condition – the competing effects of magnetic shear angle and plasma beta – to determine how jets may affect magnetopause reconnection in a statistical sense. We find that, due to their increased beta, jet plasma is typically not favourable to reconnection, often more so than the non-jet magnetosheath. Most jets do contain some reconnection-favourable plasma, however, suggesting that jets may be able to both trigger and suppress magnetopause reconnection. We complement this with new case studies of jets interacting with the magnetopause.
Predictability of temperature extremes in Europe and biases in Rossby wave amplitude
Authors: Fragkoulidis Georgios , Doensen Onno , Wirth Volkmar
Published: March 2022

This study investigates the medium-range predictability of persistent warm and cold extremes in Europe. To that end, deterministic ERA5 reforecasts for the period 1979-2019 are compared to the reanalysis of the respective period, thus providing a large sample for verification and bias identification. The seasonally-varying Gilbert skill score of both extreme event types reveals that cold extremes in summer exhibit particularly low predictability. A spatial variability also emerges for these scores with persistent extremes in northeastern Europe and Scandinavia generally achieving better predictability compared to other regions of Europe. Composites of basic reanalysis fields and their errors suggest that the aforementioned spatiotemporal variability in predictability is associated with differences in the typical synoptic conditions of each type of event. Moreover, it is shown that summer and winter in Europe suffer from a negative and positive bias in Rossby wave amplitude, respectively. Although the physical processes and model deficiencies involved are not straightforward to identify, we hypothesize that these biases constitute one of the factors that limit the predictability of temperature extremes at weather time scales.
Abrupt climate events recorded in speleothems from the ante penultimate glacial
Authors: Skiba Vanessa , Trüssel Martin , Plessen Birgit , Spötl Christoph , Eichstädter René , Schröder-Ritzrau Andrea , Braun Tobias , Mitsui Takahito , Frank Norbert , Boers Niklas , Marwan Norbert , Fohlmeister Jens
Published: March 2022

Millennial-scale climate variability, especially abrupt stadial-interstadial transitions, are a prominent feature of the last glacial as recorded in Greenland ice core records (Dansgaard-Oeschger events). Event abruptness and presence of statistical early warning signals before these transitions indicate that they involve repeated crossing of a tipping point of the climate system. However, only little information is available for periods before the last glacial period as Greenland ice cores and many other high-resolution records do not extent beyond the last glacial cycle. Given the lack of understanding of the triggering mechanism responsible for glacial millennial-scale variability with palaeoclimate data from the last glacial, it is essential to investigate this phenomenon during earlier glacial periods.

Here, we present a new highly resolved, precisely U-Th-dated speleothem oxygen isotope record from the Northern European Alps, a region which has been previously shown to resemble the glacial millennial-scale climate variability obtained from Greenland ice core records very well. Our new data covers the time interval from the ante-penultimate glacial to the penultimate glacial (MIS8-MIS6) with a high degree of replication. For both glacial periods, we find phases of pronounced millennial-scale variability but also several, ~10 ka long phases with the climate system being exclusively in stadial conditions. We compare our data with conceptual model results and investigate the occurrence and absence of abrupt climate transitions of the last 300,000 a.
The impact of peatland wildfires on soil acidity
Authors: Marcotte Abbey L. , Limpens Juul , Stoof Cathelijne , Stoorvogel Jetse
Published: March 2022

Wildfire in peatlands is of global importance due to the risk of direct carbon release. While considerable attention is given to carbon release, other wildfire impacts and indirect risks, such as the impact on soil pH, remain less studied. Peatlands characteristically require acidic conditions (soil pH ≤ 4.5) for optimal functioning. However, wildfire-produced ash often has a high pH and ash input into soil could potentially increase soil pH.

We studied a wildfire in a raised-bog peatland in the south of the Netherlands – where considerable peat smoldering and ash production occurred – by combining field observations with lab experiments. We measured the pH of topsoil and ash samples, which were collected from the area approximately two months after the wildfire. A smoldering experiment with peat was done to estimate the alkalinity in freshly produced ash (herein: ‘fresh ash’) and to able to compare it to ash collected in the field (herein: 'aged ash'). Finally, the amount of fresh ash needed to increase soil pH was quantified in an incubation and titration experiment with ash and peat soil.

All topsoil samples collected from the field were acidic (pH ~3-4), even in sampling locations with ash present. Fresh ash produced in the smouldering experiment was alkaline, while aged ash collected during field work was slightly acidic. This indicates that alkalinity was likely leached from the ash by the time of field work. The incubation experiments showed that a ≥3 cm ash layer is needed to increase soil pH by at least 1 unit. Results suggest that ash, when produced in high enough quantity, can change peatland soil pH. However, dilution and ageing of the ash after a wildfire, as likely occurred in our field site, will constrain the period of elevated soil pH after wildfires and subsequent ash input. This transit increase in soil pH suggests that even wildfires with considerable ash production do not lead to increased soil pH.
Impacts of Sea Spray in a coupled ocean-wave-atmosphere model : Mediterranean Sea case studies
Authors: Brumer Sophia , Bouin Marie-Noelle , Cathelain Marie , Leckler Fabien , Branger Hubert , Piazolla Jacques , Veron Fabrice , Michelet Nicolas , Filipot Jean-François , Redelsperger Jean-Luc
Published: March 2022

With the flourishing of offshore wind projects there is a new socio-economic interest to better our knowledge and forecasting ability of winds within the coastal marine atmospheric boundary layer (MABL). Air-sea fluxes of enthalpy and momentum greatly influence the turbulent and mean winds in the MABL. Already at moderate but certainly at high winds, wave breaking is a key driver of air-sea fluxes and the sea spray generated by whitecaps is thought to be a crucial component when modelling air-sea interactions. Most studies so far have focused on the role of sea spray in enhancing tropical cyclone intensity.  Here we investigate its impacts on the MABL under strong orographic wind forcing. A coupled model framework was developed within the scope of the CASSIOWPE project aiming at characterizing the physical environment in the Gulf of Lion (NW Mediterranean Sea) in the prospective of future floating wind farms development. It consists of the non-hydrostatic mesoscale atmospheric model of the French research community Meso-NH, the 3rd generation wave model WAVEWATCH III®, and the oceanic model CROCO. Sea-spray physics were incorporated into the Meso-NH’s surface model SURFEX. Added parametrizations will be detailed and a series of test cases will be presented to illustrate how sea spray alters the MABL under Mistral and Tramontane winds. Several sea-state dependent sea spray generation functions (SSGF) are considered in the present study. The variability in simulated fields linked to the choice of wave forcing or coupling will be showcased to evaluate their suitability in varying fetch conditions. Sea spray production remains to be adequately quantified. Existing measurement derived SSGFs span several orders of magnitude resulting in uncertainties in simulated fields which will be discussed.
Persistence in Mean Monthly Temperatures in France
Authors: Avrillaud Salomé , Olafsson Haraldur
Published: March 2022

Persistence may be regarded as a baseline to forecasting, not only at short time-scales, but on subseasonal to seasonal time scales as well.  The present study explores the persistence of monthly mean temperatures in the dense network of long time series in metropolitan France.  The data reveals very high persistence in coastal areas, both at the Mediterranean Sea and at the Atlantic coast.  However, this persistence has a high seasonal variability; it is very high in the summer, but low in the winter, suggesting strong dependence of the persistence on static stability.  There are signs of negative correlation between mean temperatures of adjacent months in the autumn in inland areas and in the winter in S-France.  These features may possibly be attributed to soil moisture and regional impact of cold spells on the atmospheric circulation.     
In situ monitoring of rain infiltration and evapotranspiration in the critical zone using self-potentials
Authors: Jougnot Damien , Loiseau Bertille , Carrière Simon , Champollion Cédric , Voytek Emily , Lesparre Nolwenn
Published: March 2022

Characterizing and monitoring water flow in the critical zone is of uttermost importance to understand the water cycle. Water link several process within critical zone from aquifer recharge and solute transfer to eco-hydrology, many eco-systemic services and biogeochemical reactions. However, the in situ quantification of water flow is technically challenging using traditional hydrological methods and numerous gaps of knowledge remain. The self-potential (SP) method is a passive geophysical method that relies on the measurement of naturally occurring electrical field. One of the contributions to the SP signal is the streaming potential, which is of particular interest in hydrogeophysics as it is directly related to both the water flow and porous medium properties. Unlike tensiometers and other point sensors, which use the measurement of state (e.g., matric pressure) at different locations to infer the intervening processes, the SP method measures signals generated by dynamic processes (e.g. water movement). However, the amplitude of the SP signal depends on multiple soil properties which are dependent to soil type, moisture content, and water chemistry (composition and pH). During the last decades, many models have been proposed to relate the SP signal to the water flow. In this contribution, we will present a soil-specific petrophysical model to describe the electrokinetic coupling generated from different water fluxes in the critical zone: rain water infiltration and water uptake from tree-roots. We tested a fully coupled hydrogeophysical approach on a large SP dataset collected in a two-dimensional array at the base of a Douglas-fir tree (Psuedotsuga menziesii) in the H.J. Andrews Experimental Forest in central Oregon, USA. We collected SP measurements over five months to provide insight on the propagation of transpiration signals into the subsurface with depth and under variable soil moisture. The coupled model, which included a root-water uptake term linked to measured sap flux, reproduced both the long-term and diel variations in SP measurements, thus confirming that SP has potential to provide spatially and temporally dense measurements of transpiration-induced changes in water flow. Similar set-ups are being installed on several test-sites of the French Critical Zone observatory network, OZCAR: Larzac, LSBB, Strengbach. This will allow us to test the approach under different climatic conditions, different soil types and in different ecohydrological systems.
Will future European large-scale circulation resemble past circulations? A methodological approach carried out with CNRM-CM6-1
Authors: Blanchet Juliette , Blanc Antoine , Boulard Jules , Creutin Jean-Dominique
Published: March 2022

Detecting trends in regional large-scale circulation (LSC) is an important challenge as LSC is a key driver of local weather conditions. In this work, we study whether future geopotential height fields projected by climate models will change in shape compared to past geopotential height fields. We consider the singularity of shape based on analogy, which is defined, for a given day, as the average distance to the 5\% closest geopotential shapes of a reference database. CNRM-CM6-1 climate model is used to study future circulations over 2015-2100 and, as reference, analogy is computed with respect to ERA5 over 1950-2014.  The results show that, over the historical period 1950-2014, CNRM-CM6-1 successfully reproduces the distribution of ERA5 singularities although it tends to produce slightly too flat -and thus slightly too singular- shapes in summer. For both databases, trends in  shapes over the historical period 1950-2014 are mainly negative but small. Over the future period 2015-2100, CNRM-CM6-1 projects significant decrease in singularity of shape for all Shared Socioeconomic Pathway scenarios, with stronger decrease for less optimistic scenarios. This tendency to more resembling shapes results from the fact that future circulations will tend to be more organized and thus less singular than in the recent past. This trend may have substantial impact on local weather, and in particular on seasonal precipitation.
Isothermal compression of an eclogite from the Western Gneiss Region (Norway): a multi-method study
Authors: Simon Martin , Pitra Pavel , Yamato Philippe , Poujol Marc
Published: March 2022

The Western Gneiss Region in Norway is constituted by a crustal nappe stack that comprises some of the best-preserved exhumed ultra-high pressure (UHP) terranes on Earth. The UHP rocks result from the subduction of the western edge of the Baltica craton beneath Laurentia during the Caledonian orogeny. Mafic eclogites form lenses within granitoid orthogneisses and show the best record of the pressure and temperature evolution. Their exhumation from the UHP conditions has been largely studied, but the prograde evolution has been rarely quantified in the eclogites although it constitutes an important constraint on the tectonic history of this area. This study focused on an unaltered eclogite sample from Vågsøy in the Nordfjord region. This sample was investigated using a large panel of methods including phase-equilibria modelling, trace-element analyses of garnet, trace- and major-element thermo-barometry and quartz-in-garnet barometry by Raman spectrometry. The eclogite comprises omphacite, garnet, white mica, epidote and amphibole and accessory rutile, quartz, zircon, carbonates and kyanite. Garnet shows a grossular-rich core with inclusions of quartz, epidote, white mica and amphibole, while grossular-poor rims are enriched in pyrope and middle rare-earth elements and include omphacite and rutile. Inclusions in garnet core point to crystallisation conditions in the amphibolite facies at 550–600 °C and 11–15 kbar, while chemical zoning in garnet suggests growth during isothermal compression up to the peak pressure of 28 kbar at 600 °C, followed by near-isobaric heating to 640–680 °C. Isothermal decompression to 8–13 kbar is recorded in fine-grained clinopyroxene-amphibole-plagioclase symplectites. The absence of a temperature increase during compression seems incompatible with the classic view of crystallization along a geothermal gradient in a subduction zone and may question the tectonic significance of eclogite-facies metamorphism. Two main tectonic scenarios are discussed to explain such an isothermal compression: (1) either the mafic rocks were originally at deep level within the lower crust and were then buried along the isothermal part of the subducting slab, or (2) the mafic rocks recorded significant tectonic overpressure at constant depth and temperature conditions during the collisional stage of the orogeny. A multi-chronometer geochronological study is currently performed and expected to bring additional, discriminant constraints on this P–T evolution. 
Citizen-science urban environmental monitoring for the development of an inter-urban environmental prediction model for the city of Los Angeles
Authors: Llaguno-Munitxa Maider , Bou-Zeid Elie , Rueda Paula , Shu Xin
Published: March 2022

High air pollution concentration levels and increased urban heat island intensity, are amongst the most critical contemporary urban health concerns. This is the reason why various municipalities are starting to invest in extensive direct air quality and microclimate sensing networks. Through the study of these datasets it has become evident that the understanding of inter-urban environmental gradients is imperative to effectively introduce urban land-use strategies to improve the environmental conditions in the neighborhoods that suffer the most, and develop city-scale urban planning solutions for a better urban health.  However, given economic limitations or divergent political views, extensive direct sensing environmental networks have yet not been implemented in most cities. While the validity of citizen science environmental datasets is often questioned given that they rely on low-cost sensing technologies and fail to incorporate sensor calibration protocols, they can offer an alternative to municipal sensing networks if the necessary Quality Assurance / Quality Control (QA/QC) protocols are put in place.

This research has focused on the development of a QA/QC protocol for the study of urban environmental data collected by the citizen science PurpleAir initiative implemented in the Bay Area and the city of Los Angeles where over 700 purple air stations have been implemented in the last years. Following the QA/QC process the PurpleAir data was studied in combination with remote sensing datasets on land surface temperature and normalized difference vegetation index, and geospatial datasets on socio-demographic and urban fabric parameters. Through a footprint-based study, and for all PurpleAir station locations, the featured variables and the buffer sizes with higher correlations have been identified to compute the inter-urban environmental gradient predictions making use of 3 supervised machine learning models: - Regression Tree Ensemble, Support Vector Machine, and a Gaussian Process Regression.