bluuebunny/crossref_metadata_2025 huggingface dataset:
Plume conduits rooted at the core-mantle boundary beneath the Réunion hotspot
Authors: Dongmo Wamba Mathurin , Romanowicz Barbara , Montagner Jean-Paul , Simons Frederik
Published: March 2022

Mid-plate volcanoes are well known as hotspots. They represent the surface signature of mantle plumes, nevertheless their origin and their role in geodynamics are still a challenge in the Earth sciences. Even though plate tectonics and mantle plumes were discovered at the same time, the latter cannot be explained by the former. Plumes’ birth, life and death play a fundamental role on the evolution of life on Earth and on plate-tectonic reorganization. La Réunion hotspot is known as one of the largest on the Earth, that created the Deccan volcanic traps in India (almost 2 million km2) and the death of more than 90% of life on the Earth including dinosaurs ~65Ma ago. So far the origin of the mantle plumes and their role in geodynamics are still unclear in Earth sciences. In that respect, we use the dataset from the French-German RHUM-RUM experiment around La Réunion hotspot (2012-2013), from IRIS data center and FDSN to extensively investigate the deep structure of the plume along its complete track from its birth to its present stage, as well as from the upper mantle to the lowermost mantle. Several shear-wave anomalies are resolved underneath Indian Ocean and the upper mantle beneath this region is fed by mantle plume rising from the core-mantle boundary. The lower mantle thermochemical dome associated to the South-African Large Low-Shear Velocity Province (LLSVP) is found to be composed of several conduits. Plume branches are highlighted at ~900 km depth. Thermal instability and thermochemical heterogeneities in the D" layer are likely the principal reasons of the plumes birth at the core-mantle boundary, and therefore an indicator of long-life of the Réunion hotspot.
Simulating the Last Glacial Cycle using a Glacial Index and Climate Matrix Method
Authors: Scherrenberg Meike D.W. , van de Wal Roderik S.W. , Berends Constantijn J. , Stap Lennert B.
Published: March 2022

For simulating ice sheet – climate interactions on multi-millennial time-scales, a set-up that uses a two-way coupled Earth System Model would be ideal. However, running these simulations over multi-millennium time-scales while including ice sheets, is not feasible. Alternatively, ice sheet models can be forced by interpolating climate time-slices, allowing for a transient forcing to an ice sheet model at limited computational costs.

Here, we compare two methods that interpolate between climate time-slices to create a transient forcing for ice sheet simulations. Firstly, we use a glacial index method, in which the climate is linearly interpolated between time-slices based only on prescribed atmospheric CO2 concentrations. Secondly, we use a climate matrix method in which the interpolation is not only dependent on the prescribed CO2 concentration, but also on internally generated thickness, volume and albedo. As a result, the climate matrix method captures ice-sheet atmosphere feedbacks.

Here we present ice sheet simulations of the Last Glacial Cycle using IMAU-ICE forced with Last Glacial Maximum (LGM) and Pre-Industrial time-slices. For the time-slices we use the output from nine Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) GCMs. Our aim is to compare and to evaluate the differences in ice sheet evolution and LGM volume and extent resulting from the different PMIP3 models and the interpolation method used for transient simulations.

For most PMIP3 forcings, both the North-American and Eurasian ice sheets build up quicker in the climate matrix method compared to the glacial index method, which is in better agreement with paleo-observations. This is mostly a result from precipitation differences between the two interpolation methods: In the climate matrix method the interpolation of precipitation is dependent on internally generated ice thickness instead of only CO2. Therefore, when ice thickness is smaller than LGM, the interpolation tends to shift more towards pre-industrial in the climate matrix method compared to the glacial index method. As precipitation is larger during pre-industrial compared to LGM in most Eurasian and North-American regions, this leads to a larger precipitation in the climate matrix method, increasing ice sheet volume. Similarly, the climate matrix method results into warmer temperatures in ice-free areas as the interpolation is dependent on both CO2, albedo and insolation. However, for most PMIP3 models, this ice sheet-temperature feedback does not cancel-out the increased precipitation in the climate matrix method.
The investigation of soil carbon sequestration and storage in forest sites on different climates in South Zala (Hungary)
Authors: Végh Péter , Bidló András , Horváth Adrienn
Published: March 2022

Due to global climate change, carbon-absorbing forests and soils will come to the fore to achieve carbon neutrality as soon as possible. Continuously increasing emissions upset the equilibrium of the atmosphere and manifest themselves in climate change or weather extremes as processes shift. Our research aimed to assess the organic carbon content stored in forest ecosystems under different climatic and forestry conditions. We focused on soil analysis because the volume of soil carbon is closely equal to the amount of carbon stored in the above-ground biomass. In the recent period, we have sampled about 12 designated forest stands to determine the amount of organic carbon stored in the soil of each forest stand. Soil samples were collected by drilling to a depth of 100 cm and 110 cm, respectively. Simultaneously with the soil sampling, the living tree stock of each stand near the sampling point was also assessed. Based on the studies carried out so far in the 12 designated forest stands, the areas can be classified into soil classes Cambisols and Luvisols (WRB 2020). The pH of the soil is mostly acidic (average = 5.2) and the texture can be determined as loam. The soil organic matter (SOM) of 0-40 cm of topsoils is 1.3%, which means ~10 t carbon content by hectares. There is still enough precipitation in the area for vegetation without disturbance; therefore, the carbon balance in the area is currently stable despite stocks are already declining due to the decline of litter amount.
Improvements of a low-cost CO2 commercial NDIR sensor for UAV atmospheric mapping applications
Authors: Liu Yunsong , Paris Jean-Daniel , Vrekoussis Mihalis , Antoniou Panayiota , Constantinides Christos , Desservettaz Maximilien , Keleshis Christos , Laurent Olivier , Leonidou Andreas , Philippon Carole , Vouterakos Panagiotis , Quéhé Pierre-Yves , Bousquet Philippe , Sciare Jean
Published: March 2022

Unmanned Aerial Vehicles (UAVs) have provided a cost-effective way to fill in gaps between in-situ (ground-based) and remote-sensing observations. In this study, a lightweight CO2 sensor system suitable for operations on board small UAVs has been developed and validated. The CO2 system autonomously performs in situ measurements, allowing for its integration into various platforms. It is based on a low-cost commercial nondispersive near-infrared (NDIR) CO2 sensor (Senseair AB, Sweden), with a total weight of 1058 g, including batteries. A series of accuracy and linearity tests showed that the precision is within ±1 ppm for 1σ at 1 Hz. Variability due to temperature and pressure changes was derived from environmental chamber experiments. Additionally, the system has been validated onboard a manned aircraft against a reference instrument (Picarro, USA), revealing an accuracy of ±2 ppm (1σ) at 1 Hz and ±1 ppm (1σ) at 1 min (0.02 Hz). Integration on a quad-copter led to improvements in the calibration strategy for practical applications. The developed system has been deployed in an intensive flight campaign (a total of 16 flights per day), with horizontal flights performed at a low altitude (100 m AGL). The designed system highlights the capacity to detect CO2 concentration changes at 1 Hz and spatial gradients and to provide accurate plume dispersion maps. It proved to be a good complementary measurement tool to the ground-based co-located observations performed by the Picarro G2401. This study gives a practical example of the process to be followed for the integration of a lightweight atmospheric sensor into a mobile (UAV) platform. Details of the measurement system and field implementations are described in this study to support future UAV platform applications for atmospheric trace gas measurements and closing the gaps in the monitoring of the current carbon cycle.
Can Degassing-induced Undercooling and Crystallisation Control Eruptible Magma Volume? 
Authors: Pistone Mattia , Arzilli Fabio , Teasdale Rachel , Brooker Richard , Iezzi Gianluca , Blundy Jonathan
Published: March 2022

Assessing the likelihood, intensity, style, and magnitude of eruptions is vital for societies living near active volcanoes worldwide. The intensity and magnitude of volcanic eruptions are controlled by multiple factors, but magma degassing upon decompression plays a critical role, causing growth of crystals that eventually lock up the magma. H2O–CO2 fluid composition modulate magma undercooling and crystallisation with H2O degassing increasing the liquidus temperature and CO2 degassing decreasing it. Using published experiments, we correlate magma undercooling with the crystal volume fraction and evaluate empirically the conditions that favour ascent of crystal-poor versus crystal-rich magmas. Magma crystallinity and undercooling are then examined for previous mafic and felsic eruptions with known erupted volumes, crystallinity of erupted tephra, and released excess SO2. The latter parameter is suggestive of excess fluid in the subvolcanic reservoir prior to eruption. We observe that H2O-rich systems with crystal volume fractions > 0.2 and undercooling > 100 °C tend to erupt ≤ 5 km3 of magma, whilst CO2-rich systems with crystal fractions < 0.2 and undercooling < 110 °C erupt > 10 km3 of magma. Our results suggest that the composition of magmatic fluids exercises an important control on eruptible volumes by suppressing or enhancing decompression crystallisation.
Geo-structural and spatial analysis on virtual outcrops for the characterization of rockslides triggered by Central Italy seismic sequence
Authors: Pignalosa Antonio , Budetta Paolo , Santo Antonio
Published: March 2022

High-magnitude earthquakes can trigger several landslides, especially in areas close to ridges and crests, where seismic ground accelerations are amplified. Such an effect was particularly evident during the long-lasting earthquake sequence of Central Italy (2016-2017), which triggered more than 1300 landslides, mainly rock slides and falls. Recent advances in 3D modelling techniques based on low-cost sensors, coupled with advances in geological and spatial analyses of 3D models, provided new opportunities to investigate such phenomena. In this study, we coupled detailed field data and up-to-date cm-scale resolution virtual outcrop models (VOMs), derived from Unmanned Aerial Vehicle (UAV) imagery, to analyse some rockfall and slides in the epicentral area of the Central Italy seismic sequence. Geostructural analyses on VOMs allowed defining the main joint orientations causing rock failures. High-resolution data also allowed to define volumes, extents of propagation areas and the topography of the failed slopes. These geometrical data together with strength parameters and assuming PGA at the sites, permitted to back-analyze both the triggering and the propagation of selected rockslides events. The results highlighted the effect of topographic amplification and complex dynamics of propagation due to rock fragmentation and debris remobilisation.
Variability of the shortening rate in Central Andes controlled by subduction dynamics and interaction between slab and overriding plate. 
Authors: Pons Michaël , Sobolev Stephan , Liu Sibiao , Neuharth Derek
Published: March 2022

The nature of the shortening of the Central Andes has been a matter of debate. The South American plate is advancing westwards forcing the subducting Nazca plate to roll back and the trench to retreat. But as the trench slowed its retreat the Andean mountain belt formed. This decrease of trench velocity has been attributed to the anchoring of the slab, but this process cannot explain the observed pulsatile behaviour of the shortening rate. Indeed, whereas the formation of the Central Andes started ~50 Ma ago, most of the shortening and elevation growth, including the formation of the Altiplano-Puna plateau, took place in two pulsatile steps at 15 Ma and 7 Ma as recognized from geological data. Thus we hypothesize that the deformation of the Central Andes is controlled by the subduction dynamics and a complex interaction between the overriding and subducting plates.

We used the FEM geodynamic code ASPECT to develop a self-consistent subduction E-W-oriented 2D high-resolution geodynamic model along the Altiplano-Puna plateau (21°S). This model incorporates the flat slab subduction episode at 35 Ma and follows the evolution of the lithospheric deformation. Our model results reproduced the observed spatial and temporal variations of tectonic shortening in Central Andes.

Three main conditions related to the plate interaction are of key importance to explain the observed shortening rate evolution in Central Andes. Firstly, the subduction dynamics affects the trench migration: each episode of slab steepening is followed by the blocking of the trench. The steepening occurs after the flat slab and at the end of two slab-buckling instabilities at 15 Ma and at 7 Ma. The second relevant process is the weakening of the overriding plate. This is ensured by the partial removal of a part of the lithospheric mantle after the re-steepening of the flat slab at 35 Ma and by weakening of the sediments in the Subandean Ranges after 10 Ma. Thirdly, a relatively high interplate friction coefficient (~0.05) is needed to ensure the stress transfer from the slab to the overriding plate, which is further enhanced by the delaminated mantle lithosphere eventually blocking the subduction corner flow.

The pulses of shortening rate occur at the end of each slab-buckling cycle when the trench is blocked. The deformation of the overriding plate is intensified by the eclogitization of the lower crust and the subsequent delamination of the sublithospheric mantle. Finally, at ~10 Ma, the deformation switches from pure-shear to simple-shear shortening, after the underthrusting of the Brazilian craton in presence of weak foreland sediments. 
Linkages between ocean circulation and the Zachariae Isstrøm in the Early Holocene
Authors: Davies Joanna , Møller Mathiasen Anders , Kristiansen Kristiane , Elnegaard Hansen Katrine , Wacker Lukas , Kristian Olsen Alstrup Aage , Lajord Munk Ole , Pearce Christof , Seidenkrantz Marit-Solveig
Published: March 2022

It is unequivocal that the climate is changing; marine terminating glaciers in Northeast Greenland (NEG) have experienced rapid speedup and retreat in recent decades as a result. The Zachariae Isstrøm (ZI) began accelerating in 2000, resulting in the total collapse of its floating ice tongue. This has been partly attributed to basal melting caused by the warming of Atlantic Water (AW). Unfortunately, our understanding of the interaction between these entities is somewhat limited by the length of instrumental records. Examining proxies preserved in marine sediment cores provides an alternative method to understand these changes on longer timescales.

Here we apply a multi-proxy approach (XRF, benthic foraminifera, stable isotopes, grain size, CT scans) to marine sediment core DA17-NG-ST08-092G, collected from the NEG continental shelf, 90km east of the ZI terminus. Our results indicate that the site was free of grounded ice at least as early as 12.5 ka cal BP, and most likely before 13.4 ka cal BP. The inflow of AW onto the continental shelf may have played a role in the seemingly early deglaciation at this site. Between 13.4 and 11.2 ka cal BP the site was overlain by a floating ice tongue, most likely the ZI, with AW and PW flowing beneath. Following this, the ZI briefly retreated westwards (11.2-10.8 ka cal BP) before it re-advanced (10.8-9.6 ka cal BP); there was a strong influx of AW throughout these periods. Between 9.6 and 7.9 ka cal BP the ZI retreated westwards again, before a drastic shift in ocean circulation occurred at 7.9 ka cal BP. At this time, there was a sharp decline in AW corresponding to an increase in PW flowing beneath perennial sea ice. In the final part of the record, AW returns and there was likely a breakup of the perennial sea ice.
Divergence in CMIP6 projections of future Arctic Ocean stratification
Authors: Muilwijk Morven , Smedsrud Lars H. , Polyakov Igor V. , Nummelin Aleksi , Heuzé Céline , Zanowski Hannah
Published: March 2022

The Arctic Ocean is strongly stratified by salinity gradients in the uppermost layers. This stratification is a key attribute of the region as it acts as an effective barrier for the vertical exchanges of Atlantic Water (AW) heat, nutrients, and CO2 between  intermediate depths and the surface of the deep Eurasian and Amerasian Basins (EB and AB). Observations show that from 1970 to 2017, the stratification in the AB has strengthened, whereas, in parts of the EB, the stratification has weakened. The strengthening of the stratification in the AB is linked to a freshening and deepening of the halocline. The weakened stratification in parts of the EB is linked to a shoaling, warming, and lack of freshening of the halocline (Atlantification). Future simulations from a suite of CMIP6 models project that under a strong greenhouse-gas forcing scenario (SSP585), the AB and EB surface freshening and AW warming continues. To meaningfully compare hydrographic changes in the simulations, we present a new indicator of stratification. We find that within the AB, there is agreement among the models that the upper layers will become more stratified in the future. However, within the EB models  diverge regarding future stratification. We discuss and detail some mechanisms responsible for these simulated discrepancies.

 
Slope-driven sediment transport of sand-mud mixtures in coastal environments 
Authors: Baar Anne
Published: March 2022

Estuaries, deltas and tidal basins are highly dynamic systems where sand and mud are transported under the complex interactions of bathymetry, currents and waves. A fundamental understanding of the formation of these coastal environments and how they will respond to changes in the future requires a better understanding of natural dynamics at the scale of individual channels and bars. The current research aims to investigate sediment transport of mud and sand mixtures at bar margins under combined waves and currents, with a particular interest in the effect of varying bedforms. To this end, experiments were conducted in an 11m long recirculating flume with an initially transversely sloped bed, representing a side-slope of a coastal sand bar. Wave intensity and mud content were systematically varied between runs. Results showed two significantly different mechanisms of sediment transport depending on the erodibility of the sediment with a clear threshold of mud content and wave intensity. During experiments with only sand, the transverse slope developed towards a flat bed over the cross-section as a result of waves stirring up the sediment and gravity pulling the sediment downslope. Symmetrical ripples formed over the width of the slope and sediment was actively transported downslope along the ripple crests. Additionally, sand waves with a longer wavelength formed in the longitudinal direction. Adding a relatively low volume of cohesive sediment did not have a significant effect on the speed at which the transverse slope decreased towards a flat bed, but there was a slower adaptation of the morphology in longitudinal direction. Ripples were three-dimensional and with highly varying dimensions based on local mud content and location on the transverse slope. With increasing mud content however, the cohesivity of the sediment mixture increased the threshold of sediment motion and only the higher part of the transverse slope experienced shear stresses that were high enough to transport sediment. Here, the mud was winnowed out of the mixture into suspension and only the sand fraction was transported downslope. Future experiments will focus on linking the direction of sediment transport under combined waves and currents to landscape development to study the larger-scale implications of the observed differences in transport mechanisms and bedform dimensions.
Predictability of rainfall in Equatorial East Africa from daily to sub-monthly time scales
Authors: Ageet Simon , H. Fink Andreas , Maranan Marlon , Walz Eva-Maria , Schulz Benedikt
Published: March 2022

Despite the enormous potential of precipitation forecasts to save lives and property in Africa, the generally low skill has limited their uptake. Where the forecasts have been used, the low skill makes the forecast-based decisions questionable at best. In particular, the performance of the forecasts is spatially and temporarily variable and therefore should not be generalised. To improve the performance of the models, and hence, their uptake, validation, analysis of possible sources of predictability and post-processing should continuously be carried out.

Here we evaluate the quality of reforecast from the European Centre for Medium-range Weather Forecasting over Equatorial East Africa (EEA). The reforecasts are initialised twice a week with lead time up to 45 days and are available from the subseasonal-to-seasonal (S2S) data base at a spatial (temporal) resolution of 1.5° (6-hourly). The evaluation is done using both satellite (Integrated Multi-satellite Retrieval for Global Precipitation Measurement) and ground-based (rain gauges) rainfall observations for the period 2000–2019. Both the raw and post-processed reforecasts are analysed, from daily to sub-monthly lead times and for temporal aggregations (48-hours and 120-hours total precipitation). To assess the skill of the reforecasts, an existing ensemble probabilistic climatology (EPC) derived from the observations is used as the reference forecast (Walz et al. 2021, doi: 10.1175/WAF-D-20-0233.1). First results show that there is potential of skill in the raw forecasts up to 10 days ahead particularly in the elevated areas of EEA. There is positive skill in the forecast of rainfall occurrence and the full rainfall distribution, i.e., the Brier Skill Score and the Continuous Rank Probability Skill Score, are positive in most areas, especially over land. As expected the skill decreases with lead time, vanishing completely between day 10 and 15. Aggregating the reforecasts enhances the scores further, likely due to reduction in time and temporal mismatches. The skill also varies seasonally with the long rains in March-April-May (the major dry season in June-July-August) having the best (worst) skill over most parts of the region. The raw reforecasts have a systematic bias, being overconfident at all lead-times. To correct for this bias, post-processing the reforecast using the isotonic distributional regression (IDR) method is applied and the improvement in performance will be discussed. Overall, initial results indicate that raw and postprocessed ECMWF S2S forecasts over EEA have more skill compared to findings in related studies for northern tropical Africa.
The onset of faulting around geometrically irregular faults
Authors: Sagy Amir , Morad Doron , H. Hatzor Yossef , Lyakhovsky Vladimir
Published: March 2022

Geological and geophysical observations indicate that fault geometry is nonplanar, includes irregularities in all directions at many scales. The geometrical heterogeneity of faults is particularly critical during the interseismic stage of the earthquake cycle because it perturbs the stress field and thus affects the rupture nucleation along the fault zone and around it. We present a new analytical solution for the static stress field around a rough interlocked interface obtained under compressional stresses, and discuss its applications to faulting and seismic hazards. The model outputs are the local stress field and the Failure-Ratio, defined here as the susceptibility to failure of the bulk material around the interface. The calculations are then obtained by the following steps: First, the interface geometry is represented by a Fourier series. Then, the stress components around the irregular interface are calculated analytically using perturbation theory for any two dimensional far-field stress tensor. Finally, the Failure Ratio at any location near the interface is estimated by adopting a Coulomb failure criterion for the bulk material.

The model results can be applied to faulting mechanics because they demonstrate how the elastic stress field around rough fault is controlled by the geometry and by the tectonic stresses. We find that under a given tectonic stress state, stress heterogeneity increases with roughness. Therefore, some zones near rough faults are expected to yield at lower tectonic shear stress comparing to zones nearby smooth ones. However, the magnitudes of these events are expected to be relatively small, as they nucleate under relatively low tectonic stresses and fail as they propagating immediately to a stress shadow. This stress distribution promotes small seismic events near rough fault and therefore we suggest that increasing heterogeneity of the surface, contributes to increasing of the b-value in Gutenberg-Richter earthquakes distribution.

We compare the model predictions with results of experiments performed on rough rock surfaces and find good agreement between the locations of off-fault deformation zones and the calculated high Failure-Ratio values. We further test the model implications for stresses and failure around a natural fault system – the San Andreas Fault and find a first-order agreement between Failure-Ratio values and earthquake distribution around this fault system. We conclude that the proposed analytical approach is a useful and practical tool for evaluating the contribution of fault geometry to the seismic hazard potential around it.

 
Developing a Decision Making Tool for Evaluating the Compatibility of Nature-Based Solutions to the Built Heritage
Authors: Kale Eda , De Groeve Marie , De Kock Tim
Published: March 2022

Historical buildings, which play a major role in shaping the urban fabric, are facing challenges due to climate change. Today the cultural values are considered among the main goals of sustainable development much like the social, economic and environmental values. Therefore it is important to discover the sustainable ways of conservation and maintenance practices on mitigating the impacts of climate change, so that the historical buildings can play an active role in achieving sustainable development goals without compromising their cultural and heritage values.

Nature-based solutions (NbS) are considered as sustainable and effective solutions on mitigating impacts of climate stressors. Exploring their compatibility to conservation practices can bring mutual opportunities to the urban fabric and to the historical buildings. However, nature has been considered as a threat amongst the conservation practices due to potential biodegradation of materials, obscuring the heritage structure and requiring an additional cost of maintenance. Nevertheless, many uses of nature-based solutions come across in history, e.g. in the form of turf or sod roofs that provide thermal insulation on extreme climate conditions. Today, there are some attempts to integrate NbS to heritage environments within the scope of retrofitting projects. Nevertheless, a comprehensive methodology of performance assessment on mitigating climate challenges without compromising the cultural and heritage values has not been developed yet.

This project aims to develop a decision making framework for heritage actors on evaluating the compatibility of NbS to conservation and maintenance practices of historical buildings that are exposed to adverse impacts of climate stressors in the urban context. For developing a general outline of the framework, various NbS will be evaluated and categorized based on quantitative data in the literature according to their aesthetic fit to historic buildings, their structural feasibility and their performance on mitigating the effects of climate stressors. Throughout the project, process and value based research will be conducted on carefully selected case studies. The selected case studies will be evaluated within the scope of determining the severity of the prevailing climate stressors in their context, their structural sensitivity and their adaptability capacity to the new interventions. Based on the results, the compatible NbS and design measures can be identified. In the later stages of the project, the feasibility of the proposed nature-based design for the case studies will be tested by monitoring and comparing the results before and after the implementation.
Boundary layer dependence of atmosphere-ocean coupling in operational weather forecast models over the marginal ice zone
Authors: Volonté Ambrogio , Methven John , Gray Suzanne L. , Harvey Ben , Martínez-Alvarado Oscar
Published: March 2022

Arctic cyclones are the dominant type of hazardous weather system affecting the Arctic environment in summer. They can also have critical impacts on sea-ice movement, sometimes resulting in ‘Very Rapid Ice Loss Events’ which present a major challenge to coupled forecasts of the Arctic environment from days out to a season ahead. In late summer the marginal ice zone is extensive and wind forcing can move the ice readily; in turn, the dynamic sea ice distribution is expected to feedback on the developing weather systems.

In summer 2022, in concert with ONR-THINICE, we aim to fly two research aircraft from Svalbard into Arctic cyclones passing over the marginal ice zone. We will measure the turbulent exchange fluxes, flying low above the interface between atmosphere and ice, at the same time as measuring the wind and cloud structure of the cyclones above and the properties of the ice below. Combining the observations with numerical modelling experiments using the Met Office NWP model, we aim to deduce the dominant physical processes acting and test theoretical mechanisms for the influence of sea ice on Arctic cyclone dynamics, with a particular focus on form drag and momentum exchange in the boundary layer.

Met Office and ECMWF forecasts that are coupled, or uncoupled, with a dynamic sea ice distribution have been investigated initially for systematic differences in the representation of boundary layer and surface fluxes, composited relative to the warm and cold sectors of Arctic cyclones and conditional on the surface beneath (ice, ocean, land). One of the key differences outlined resides in the increased strength of surface (10m) winds over ice, including marginal ice, in coupled Met Office forecasts when compared against their uncoupled counterparts. Initial analysis links this discrepancy with a difference in the degree of stability of the boundary layer. A more stable profile is observed in the coupled forecasts, associated with lower temperature at 1.5m and smaller wind rotation with height. These findings help us to focus the objectives of the research flights and measurements and, in consequence, inform the flight and observation plans for the field experiment.
Point Mass Balance Regression using Deep Neural Networks: A Transfer Learning Approach
Authors: Anilkumar Ritu , Bharti Rishikesh , Chutia Dibyajyoti
Published: March 2022

The last few years have seen an increasing number of studies modeling glacier evolution using deep learning. Most of these techniques have focussed on artificial neural networks (ANN) that are capable of providing a regressed value of mass balance using topographic and meteorological input features. The large number of parameters in an ANN demands a large dataset for training the parameter values. This is relatively difficult to achieve for regions with a sparse in-situ data measurement set up such as the Himalayas. For example, of the 14326 point mass balance measurements obtained from the Fluctuations of Glaciers database for the period of 1950-2020 for glaciers between 60S and 60N, a mere 362 points over four glaciers exist for the Himalayan region. These are insufficient to train complex neural network architectures over the region. We attempt to overcome this data hurdle by using transfer learning. Here, the parameters are first trained over the 9584 points in the Alps following which the weights were used for retraining for the Himalayan data points. Fourteen meteorological from the ERA5Land monthly averaged reanalysis data were used as input features for the study. A 70-30 split of the training and testing set was maintained to ensure the authenticity of the accuracy estimates via independent testing. Estimates are assessed on a glacier scale in the temporal domain to assess the feasibility of using deep learning to fill temporal gaps in data. Our method is also compared with other machine learning algorithms such as random forest-based regression and support vector-based regression and we observe that the complexity of the dataset is better represented by the neural network architecture. With an overall normalized root mean squared loss consistently less than 0.09, our results suggest the capability of deep learning to fill the temporal data gaps over the glaciers and potentially reduce the spatial gap on a regional scale.
The extreme heat wave of 2021 in Greece: intensity, duration, cumulative heat and all-time records on centennial scale
Authors: Founda Dimitra , Katavoutas George , Pierros Fragiskos , Mihalopoulos Nikolaos
Published: March 2022

Heat waves (HWs) rank among the most dangerous weather phenomena, with catastrophic impacts on societies and ecosystems. Since the beginning of the 21th century, many regions worldwide have been experiencing unprecedented extreme heat episodes. The Mediterranean countries in particular, are very prominent and vulnerable to climate change and heat-related risk. During summer 2021, Greece faced one of the worst HWs in its modern history, with exceptionally high temperatures prevailing from July 28th to August 6th. The special characteristics and the rarity of this event have been highlighted and evaluated through the historical climatic record of the National Observatory of Athens (NOA), dating since the mid 19th century.

The study analysed daily maximum (Tmax), mean (Tmean) and minimum (Tmin) air temperatures of the historical record, and estimated several indices of all HW episodes detected during the study period. The analysis showed that the HW of 2021 (HW2021) exceeded all previous records in a number of indices concerning the persistence, amplitude, mean intensity of HWs (based on Tmean and Tmin thresholds), but also ‘cumulative heat’ (an index combining both intensity and duration of a HW). Specifically, HW2021 was found to be the longest HW ever recorded at NOA (since the mid 19th century), with a total duration of 10 days. The amplitude of HW2021 (maximum temperature of the hottest day) was 43.9 0 C, representing the second highest temperature ever recorded at NOA, following the absolute record value of 44.8 0 C observed on June 26th 2007.

The most prominent features of HW2021 include the maintenance of very high temperatures throughout the whole 24-hour period and especially the elevated nighttime temperatures, inherent to the additive effect of the urban heat island in the city of Athens. The values of 31.6 and 36.5 0C for the daily minimum and mean temperatures respectively, represent the highest values ever recorded at NOA. National all-time temperature records were observed in other Greek stations, with maximum temperatures reaching up to 47 0C.  The prolonged hot and dry conditions triggered the ignition of catastrophic wildfires in Greece, with dramatic environmental and economic loss.
Accounting for the impact of slope on fire spread in a dynamic global vegetation model
Authors: Oberhagemann Luke , Drueke Markus , Billing Maik , von Bloh Werner , Sakschewski Boris , Rust Henning , Thonicke Kirsten
Published: March 2022

Fire modelling incorporated into global dynamic vegetation models (DGVMs) allows for the projection of changes to fire-related biogeophysical and biogechemical processes under future climate scenarios, including anthropogenic climate change. Due to the large grid sizes often required to efficiently model fire and vegetation dynamics in a global manner, fire-enabled DGVMs generally neglect some finer-scale effects, including slope. However, slope can have a significant impact on the spread of individual fires and, therefore, the global area burned. As a fire moves uphill, the angle of flames is better suited to heating nearby fuel, thus increasing the rate of spread relative to fires on level ground. In this study, we apply a function to account for the impact of slope on fire spread in the SPITFIRE model incorporated into the LPJmL5.3 DGVM to improve the calculation of fire-related processes, including burnt area. We aggregate slope data across a grid cell to account for the impact of slope in a general way appropriate to the  grid size used in SPITFIRE. Our approach, while focused on the SPITFIRE model, may also be applicable to other DGVM-based fire models.
Constraining Seismic Anisotropy on Mars: New Challenges and First Detection 
Authors: Beghein Caroline , Li Jiaqi , Wookey James , Davis Paul , Lognonné Philippe , Schimmel Martin , Stutzmann Eléonore , Golombek Matthew , Montagner Jean-Paul , Banerdt William
Published: March 2022

Seismic anisotropy is now commonly studied on Earth and has been detected at various depths, from the crust to the top of the lower mantle, in the lowermost mantle, and in the inner core. In the mantle, observations of seismic anisotropy are often taken as an indication of past or present deformation resulting in the preferential orientation of anisotropic minerals. In the crust, it can come from stress-induced oriented cracks, compositional layering, or crystallographic preferred orientation of minerals. 

While many questions remain regarding the presence and interpretation of seismic anisotropy on Earth, scientists are now faced with new, exciting challenges in trying to constrain the structure of other planetary bodies. One of the goals of NASA’s InSight mission, which landed on Mars in November 2018 and includes a very broadband seismometer, is to constrain Mars interior structure. Compared to seismic studies of Earth, which benefit from the availability of a wealth of high quality data recorded on many seismic stations, difficulties with InSight stem from having only one seismic instrument and only a few high quality events. 

In this study, we analyzed the horizontally polarized (SH)-wave reflections generated from the shallowest crustal layer (layer 1) detected at 8 ± 2 km beneath the InSight lander site by a previous receiver function (RF) study. From Sol 105, when the first low-frequency marsquake was recorded, to Sol 1094, a total of 83 broadband and low-frequency events were detected, but only nine are rated as quality-A with constraints on both their epicentral distance and back azimuth. Of those nine events, we selected four that did not show any interference with mantle triplications generated by the olivine to the wadsleyite phase transition and that had a clear signal after the direct SH phase. A model space search approach enabled us to obtain a range of acceptable SH-wave velocities and layer thicknesses, which we then compared with the RF models of Knapmeyer-Endrun et al. (2021). We found that the acceptable SH-wave speeds are systematically lower than those from the RF study. Since this RF analysis is sensitive to vertically polarized (SV)-waves, we interpret this difference as the signature of radial anisotropy with an anisotropy coefficient 𝜉=(𝑉𝑆𝐻/𝑉𝑆𝑉)2 between 0.7 and 0.9. Modeling of preferred alignment of inclusions shows that dry or fluid-filled cracks/fractures, and igneous inclusions can reproduce the observed radial anisotropy amplitude with VSV>VSH. 
The Resonant Tidal Evolution of the Earth-Moon Distance
Authors: Farhat Mohammad , Auclair-Desrotour Pierre , Boué Gwenaël , Laskar Jacques
Published: March 2022

Due to tidal interactions in the Earth-Moon system, the spin of the Earth slows down with time and the Moon drifts away. This present recession of the Moon is now measured with great precision using Lunar Laser Ranging, but it has been realised, more than fifty years ago, that simple solid-Earth tidal models extrapolated backwards in time lead to an age of the Moon that is by far incompatible with the geochronological and geochemical evidence. Since then, in order to evade this paradox, more elaborated models have been proposed, taking into account the tidal frequency-dependent oceanic dissipation; but none so far has been able to fit both the estimated lunar age and the present rate of lunar recession. In this talk, we present a physical model that reconciles these two constraints and yields a unique solution of the tidal history. This solution fits remarkably well the available geological proxies and consolidates the cyclostratigraphic method, although such a fit was not imposed. The resulting evolution involves multiple crossings of resonances in the oceanic dissipation that are associated with significant and rapid variations in the lunar orbital distance, the Earth’s length of the day, obliquity, and precession frequency. 
Exploring the driving factors of CH4 and CO2 emissions in coastal wetlands: a case study in the Ravenna Province, Italy
Authors: Chiapponi Emilia , Giambastiani Beatrice M.S. , Zannoni Denis , Antonellini Marco , Silvestri Sonia
Published: March 2022

Coastal wetlands play a strategic role in the context of mitigating climate-change thanks to their ability of sequestering large amounts of organic carbon (C) and store it in the ground. However, methane (CH4) may form in the sediments of freshwater wetlands, so that these ecosystems may switch from a net sink to a net source of greenhouse gases (GHGs). Salinity is known to be one of the main inhibitors of CH4 production; however, its influence in brackish water systems is still poorly studied. Our study aims at understanding how the consequences of climate change (sea-level rise, salinization, and temperature increase) may affect the C storage in vegetated coastal wetlands.

Here we present the results of almost one year of measurements performed in four wetlands located along the northeast Adriatic coast near Ravenna, Italy. Despite a very limited distance among the four sites (1-4 km), they present a significant salinity gradient, going from fresh- to brackish waters. Air and soil temperatures and solar irradiance were continuously monitored through a network of sensors. Carbon dioxide (CO2) and CH4 fluxes from soils and waters, water head levels, surface, and ground water physical-chemical parameters (redox potential (Eh), temperature (T), pH, conductivity (EC), sulphate and sulfide concentrations) were measured monthly. Finally, soil samples were collected at each site in order to determine soil properties, i.e. organic matter content, bulk density, granulometry. 

We used multivariate statistics to investigate emergent relationships between GHGs fluxes from water and soil and environmental factors. The results of the principal component analysis (PCA) suggest that air T, water T  and irradiance play a significant role in both CH4 and CO2 emissions from water and soil. On the other hand, water head level and EC have been found to be limiting factors of the GHGs emissions. Soil properties seem to be secondary factors both in soil and water emissions.

The results obtained from these and other analyses will be presented to provide a critical insight on correlations between GHGs emissions and the environmental drivers in temperate coastal wetlands. A remote-sensing approach to upscale the results obtained on the four studied wetlands, to the adjacent coastal wetland system will also be presented. Remote sensing turns out to be a key method to extend the assessment on C fluxes to areas difficult to access and that could not be characterized otherwise.
Remote sensing – based analysis of the islands dynamics in the Lower Danube River
Authors: Virghileanu Marina , Ioana-Toroimac Gabriela
Published: March 2022

River islands are important components of the river morpho-dynamics, which can provide essential information on fluvial processes, as well as on sediment and flow regimes. In the same time, river islands play an essential role from the political, environmental and socio-cultural points of view. Thus, understanding the temporal dynamics of the river islands is a required task for channel navigation safety, port functionality, agricultural production and biodiversity. The aim of this study is to analyse the spatial and temporal changes on the river islands during the last 40 years, based on satellite remotely sensed images. The study focuses on the Lower Danube River, downstream the Iron Gates dams altering the flow and sediment load, which also suffers from dredging for navigation. The islands of the Lower Danube River generate major impacts on riparian states relationship, interfere with the ports activity and EU investments (as it is the case of Rast port in Romania), or are the subject of ecological restoration. Multispectral satellite data, including Landsat and Sentinel-2 images, were used for river islands mapping at different temporal moments, with a medium spatial resolution (up to 15 m on Landsat pansharpened data and 10 m on Sentinel-2). Spectral indices, as NDVI and NDWI, allowed the automatic extraction of island boundaries and land cover information. On these, two processes were carried out: 1) the characterization of the river islands morphology, and 2) the quantification of the spatial and temporal changes over time. The resulted data are connected with in-situ measurements on flow regime and sediment supply, as well as with flood events and human activities in order to identify the potential drivers of change. The results demonstrate a strong correlation between river islands dynamics and flood events in the Lower Danube River, as the major flood event from 2006 significantly modified the islands size and shape. This research can allow the identification of the evolutionary model of the Danube River.

 

This research work was conducted as part of the project PCE 164/2021 “State, Communities and Nature of the Lower Danube Islands: An Environmental History (1830-2020)”, financed by the UEFISCDI.