HAL-INSU
Not a member yet
203706 research outputs found
Sort by
WALLABY pilot survey: the extensive interaction of NGC 4532 and DDO 137 with the Virgo cluster
No full textInternational audienceABSTRACT As part of the pilot survey of the Widefield ASKAP L-band Legacy All-sky Survey (WALLABY), high-resolution neutral atomic hydrogen (HI) observations of the dwarf galaxy pair NGC 4532/DDO 137 (WALLABY J123424+062511) have revealed a huge (48 kpc) bridge of gas between the two galaxies, as well as numerous arms and clouds that connect with the even longer (0.5 Mpc) tail of gas previously discovered with the Arecibo telescope. Our modelling suggests that a combination of ram pressure and tidal forces is responsible for the nature of the system. Although the pair lies well outside of the virial radius of the Virgo cluster, ram pressure due to infall through an extensive envelope of hot gas around the cluster is most likely responsible for the HI tail. Over a time-scale of 1 Gyr, the predicted electron density ( cm) and infall velocity (880 km s) are probably sufficient to explain the extensive stripping from the common gaseous envelope of NGC 4532/DDO 137. The ongoing tidal interaction with the Virgo cluster appears to have prevented a rapid merger of the binary pair, with the mutual tidal interaction between the galaxy pair being responsible for raising gas from the outer parts of the galaxy potential wells into the HI bridge and common envelope. The NGC 4532/DDO 137 system mirrors many of the physical features of the Magellanic System, and may lead to a better understanding of that system, as well as casting more light on the relative importance of interaction mechanisms in the outskirts of dynamically young galaxy clusters such as Virgo
Simulating generic agrivoltaic systems with ORCHIDEE: Model development and multi-case study insights
No full textInternational audienceAgrivoltaics (AVs) has emerged as a promising solution to address the competing demands for land, energy, and food production within the Water-Energy-Food-Ecosystem (WEFE) nexus. However, its effects depend on climate, crops and local conditions, requiring large-scale models capable of capturing these variations. For this purpose, our study introduces a new regional-scale AV model, at the interface with regional climate models and the Organizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model, to explore the interactions between climate, AV systems and crops within the WEFE nexus. The model is applied to two AV configurations across three distinct climates (dry, wet, and climatological) over the Iberian Peninsula and The Netherlands , using two generic crop types. The results reveal that in arid regions with high solar radiation, such as in the southern Iberian Peninsula, AV systems offer many advantages, particularly in dry years: increased crop productivity, enhanced food security and better use of water and land, whileproducing renewable energy. In contrast, in The Netherlands , characterized by abundant rainfall and lower solar radiation, AV systems tend to reduce crop productivity, and the gains in terms of water and land use are less marked. These findings highlight the model ability to assess AV systems by capturing regional specificity and varying responses to different climatic contexts. They suggest that optimizing AV system designs involves a nuanced approach, carefully balancing the synergies across energy production, agricultural productivity, and resource use while managing the trade-offs inherent to different climatic conditions
Rising power system strains despite decreasing heating demand in a warming climate
No full textInternational audienceElectrifying systems like heating is essential for reducing greenhouse gas emissions. France provides a compelling case study due to the high share of electricity used in its buildings sector. Using a heating degree-days methodology alongside a power demand model applied to ten climate model simulations, we examine four emission scenarios, assuming the actual electricity mix and use. Our results indicate a significant decrease in average power demand, with a slight reduction in peak demand during cold waves, driven by rising winter temperatures. This trend may give the misleading perception of a reduction in grid constraints. However, counterintuitively, the demand surge during cold waves—relative to normal conditions—is projected to increase with climate change, which could heighten the pressure on the power system. With the probability of such events decreasing, and heating needs becoming more fragmented, adaptation will be crucial for power system preparedness
Impact of water table fluctuations on the redistribution of light hydrocarbons
No full textInternational audienc
Comparative paleoclimatic reconstruction of Western and Southern Europe Glacial Ecosystems using inverse modeling of loess δ13Corg
No full textInternship reportInternational audienceThe Pleistocene marks the period during which the genus Homo emerged on earth. This period is characterized by the advent of strong oscillations in temperature, with a periodicity of ca. 100 000 years over the past 1 million years. Major environmental changes associated with these climatic cycles likely determined the history of Homo sapiens migration and evolution. Understanding the evolution of past climate and how the environment and mankind have adapted to it is a key feature to be able to predict the potential evolution of today’s climate and its possible consequences on our environment. Paleoclimatology offers the long-term records necessary to reconstruct climatic and environmental conditions on a thousand of years’ time scale. The aim of this project was to reconstruct the values of temperature and precipitations during the two last glacial-interglacial cycles in Europe based on loess archives at the sites of Villiers-Adam (France) and Harletz (Bulgaria). The reconstruction was done by inverse modeling of loess stable carbon isotope measurements. An existing Bayesian inference program was modified to optimize it for use with loess δ13Corg data and hard climate conditions during the glacial stages. The inversion algorithm is based on the BIOME4 vegetation model predictions for the δ13C and biome, given the climate and the geophysical properties of the site. The modified version of the program could reconstruct temperature and precipitation values for the site of Villiers-Adam during the period from Late Saalian to Weichselian Upper Pleniglacial, with yearly temperatures ranging between -26 and -8°C and yearly precipitations ranging between 75 to 300 mm. The reconstructed parameter’s time course nicely retraced the major inflections of the δ13Corg data which seemingly correspond to climatic changes all over Europe. The program could not converge for the site of Harletz. A probable reason is the exclusion of the presence of C4 plants in the simulation, which might bring to an incompatibility between the δ13Corg values and the range of possible climates at that latitude. The inclusion of δ13Corg of C4 plants in the program may be needed to reconstruct the parameters of this site
The late rise of sky-island vegetation in the European Alps
No full textInternational audienceOur understanding of the emergence of mountain floras rests on our ability to infer how orogeny, landscape dynamics and climate change altered their evolutionary trajectories. Here, we reconstruct the assembly of the diverse sky-island flora of the European Alps and test the impact of key geo-climatic events. We use a dated 5,231-species phylogeny, including 96% of the sky-island flora. The assembly of this flora occurred through the colonisation of over a thousand distinct lineages, of which 46% speciated from their lowland ancestor and 6% underwent in situ cladogenesis. The young ages of extant sky-islands lineages show that their accumulation was decoupled from ancient geo-climatic events, but accelerated throughout the Plio-Pleistocene. The sky-island vegetation therefore assembled through recent lineage turnover, which was triggered, rather than impeded, by Pleistocene glacial intensification. This perspective challenges previous assumptions and highlights the complex interplay of geo-climatic factors in shaping the intricate tapestry of alpine floras
Thallium cycling and boundary exchange in a continental margin basin
No full textInternational audienceThallium (Tl) isotopes are a robust tracer of ancient ocean oxygenation through their link to the burial flux of deep-sea manganese oxide minerals. Yet, the details of Tl geochemistry at the continental margin remain largely unexplored, hindering quantitative application of the palaeoredox proxy. To develop our understanding of Tl diagenesis, phase dynamics, and mass transfer at the continent-ocean interface, we collected sediments from three sites in the perenially oxic Skagerrak sea as well as sediments and suspended particles from five adjacent rivers. The three Skagerrak sediment sites are biogeochemically diverse, with variable oxygen penetration (9–18 mm) and C-oxidation occurring predominantly through either sulfate, iron, or manganese reduction. Sequential extractions and porewater analyses reveal a highly homogeneous abundance and phase association pattern of Tl across all sample types and sites. Sediment and particle Tl resides almost exclusively in acid-leachable aluminous clays and residual crystalline phases. We interpret these phases to be terrigenous, except at the highly Mn-enriched site S9 where we find up to ∼45 % of Tl is authigenic. This claim is supported by Tl isotopic compositions of acid-leachable sediment (ε205TlHNO3), which average –2.5 ± 0.9‱, within uncertainty of the average upper crust value of –2.0 ± 0.5‱ and a regional riverine particle delivery value of –2.1 ± 1.2‱.Incubations of Skagerrak sediments with added bottom water Tl reveal a fractionation factor (α) of ∼1.0007, amounting to an isotope ratio difference of ∼7‱. A comparable fractionation of 2.4 to 4.5‱ is calculated for authigenic Tl removal in the Skagerrak sediments. However, this fractionation is lower than that observed in deep sea pelagic clays and hydrogenetic Mn crusts and nodules (α ∼1.0021), yet significantly higher than expected for mature diagenetic Mn oxides like triclinic birnessite and todorokite (α ∼1.00005). Thallium cycling is largely decoupled from Mn diagenesis at our marine sites and only associates weakly with the active sedimentary Mn recycling. Rather, effluxing of dissolved Tl is observed at all sites. We employ a diagenetic reaction-transport model to quantify dissolved Tl fluxes and compare these fluxes with independent assessments of Tl mass balance based on authigenic/terrigenous Tl proportions. We find that within the oxic Skagerrak basin, sediments may be both true sources and, if Mn-enriched, true sinks of Tl, with extrapolated flux magnitudes relevant to marine Tl mass balances. Our study presents a much-needed description of Tl diagenesis in diffusive margin sediments and suggests that hitherto unrecognized sources of originally terrigenous Tl to the marine environment may occur at the continent-ocean boundary, either via the release of labile clay-bound Tl directly from riverine particles or during sediment diagenesis
Extending the utility of the Tl isotope paleoredox proxy to carbonates
No full textInternational audienceThallium isotope ratios (205Tl/203Tl) recovered from ancient marine shales are able to provide novel information about Earth’s ocean oxygenation history. Here we demonstrate the potential to extend this utility to the ancient carbonate record. We present Tl concentration and isotope ratio data for modern and geologically recent carbonates from the Great Bahama Bank that capture initial carbonate deposition to diagenesis on multiple scales. Young carbonates from bank-top cores reveal bulk Tl isotope compositions (ε205Tl) that are either indistinguishable from today’s globally homogenous seawater value (ε205Tl = –6.0 ± 0.3‱) or within 0.4‱. Older carbonates from the deeper and diagenetically altered cores also oftentimes capture seawater ε205Tl values. Carbonates with high dolomite contents are the most reliable archives, revealing with only minor exception ε205Tl values within analytical error of modern seawater. Meteoric diagenesis predictably drives carbonate ε205Tl values higher and toward the average composition of global freshwaters (ε205Tl ≈ –2‱). Our findings suggest that properly screened ancient carbonates can be viable archives of past seawater ε205Tl values. These seawater ε205Tl values are set by past marine Tl isotope mass-balance, which is sensitive to manganese oxide burial on the seafloor and hence past levels of global bottom water ocean oxygenation
An integrated multi-instrument methodology for studying marginal ice zone dynamics and wave-ice interactions
No full textWave-driven fragmentation is the key mechanism shaping the Marginal Ice Zone (MIZ). Capturing this process is therefore essential for improving sea ice models, which currently do not fully capture the complex interactions between the forcing imposed by waves and the nonlinear dynamics of the resulting sea ice breakup and deformation. To investigate these interactions, we introduce a comprehensive multi-instrument dataset from a field campaign in the MIZ of the St. Lawrence Estuary, Canada, designed to characterize wave propagation and mechanical properties of sea ice under natural forcing conditions. The dataset integrates synchronized measurements from geophone arrays, wave buoys, smartphones configured as motion sensors, and unmanned aerial vehicles (UAVs), all collected during coordinated deployments across diverse ice types and sea states. Seismic data, recorded with geophone arrays, enable estimation of the ice thickness and elastic properties via active and passive wavefield analyses. Concurrently, wave buoys and smartphones capture ocean wave characteristics including amplitude, wavelength, and attenuation near ice edges. UAV imagery is processed with advanced methods to detect vertical ice displacements with sub-centimetre sensitivity, allowing extraction of wave dispersion relations in different ice conditions. Preliminary analyses demonstrate strong agreement between independent measurement methods, validating the dataset’s quality. This multi-sensor approach offers unique opportunities to improve our understanding of wave-ice interactions, wave attenuation, and fracture dynamics in situ, thus offering a valuable resource for the sea ice and oceanographic research community to gain insight in wave-induced ice break-up mechanisms under natural conditions
TOI-2407 b: a warm Neptune in the desert
No full textInternational audienceABSTRACT We present the validation of TOI-2407 b, a warm Neptune-sized planet with a radius of R, orbiting an early M-type star with a period of 2.7 d and an equilibrium temperature of K. The planet was identified by Transiting Exoplanet Survey Satellite (TESS) photometry and validated in this work through multiwavelength ground-based follow-up observations. We include an observation with the novel complementary metal-oxide-semiconductor (CMOS)-based infrared instrument SPeculoos InfraRed Imager for Transits (SPIRIT) at the Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) Southern Observatory. The high-precision transit data enabled by CMOS detectors underscore their potential for improving the detection and characterization of exoplanets orbiting M-dwarfs, particularly in the infrared, where these stars emit most of their radiation. TOI-2407 b lies within the boundaries of the period–radius Neptune desert, an apparent scarcity of Neptune-sized planets at short orbits. Further characterization of TOI-2407 b, such as radial-velocity measurements, will refine its position within planetary demographic trends. This system also provides a comparison case for the well-studied Neptune-sized planet Gliese 436 b, of similar radius, period and stellar type. Comparison studies could aid the understanding of the formation and evolution of Neptune-like planets around M-dwarfs