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150 ans d’instrumentation solaire sol à l’Observatoire de Meudon (1876-2026)
No full textDocument d'histoire des sciences relatant 150 ans d'instrumentation pour l'observation du Soleil à l'observatoire de Meudon, section d'Astrophysique de l'observatoire de Paris, à l'occasion des 150 ans du site de Meudon en 2026Le Soleil est observé à la lunette depuis quatre siècles. Cependant, son étude a fait un bond prodigieux à la fin du XIX ème siècle avec l'apparition de la photographie et de la spectroscopie, puis au début du siècle suivant avec l'invention du coronographe et des filtres monochromatiques, et enfin dans la seconde moitié du XX ème avec l'avènement des grands télescopes au sol et de l'exploration spatiale. Cet article retrace les grandes étapes des développements instrumentaux solaires à Meudon, depuis sa fondation par Jules Janssen en 1876 jusqu'à nos jours, en se limitant à l'instrumentation sol ou ballon, conçue à Meudon et installée à Meudon ou en d'autres lieux (Nançay, Pic du Midi, Canaries). Les Meudonnais ont joué un rôle pionnier dans l'histoire de la physique solaire par l'expérimentation de techniques innovantes. Après l'âge d'or des inventions, vint le temps des grands instruments, étudiés à Meudon mais souvent installés dans des sites plus favorables, et celui du spatial, dans un cadre de collaboration internationale, mais que nous n'abordons pas ici
Surface ice texture mapping of Planpincieux glacier reveals spatial mechanical heterogeneities
No full textInternational audienceCrystallographic textures or Crystal Preferred Orientations (CPO) of glacier ice significantly influence its mechanical behavior by transferring mechanical anisotropy from the single-crystal scale to the macroscopic scale. However, their spatial variability and impact on fluidity remain poorly constrained in temperate glaciers. This study presents a detailed mapping of surface crystallographic textures on the Planpincieux Glacier (Mont Blanc Massif, Italy), combining field measurements, surface velocity data, and numerical modeling to assess mechanical heterogeneities. Six sampling zones were analyzed using an Automatic Ice Texture Analyser (AITA), revealing distinct crystallographic texture patterns linked to local strain configurations and boundary conditions. Weak crystallographic textures in zones near the glacier margins and crevasse areas suggest limited viscous deformation, while stronger crystallographic textures indicate deformation under various shear boundary conditions with impact of dynamic recrystallization. The resulting textures are associated with a fluidity enhancement factor reaching up to 2.3 and a fluidity anisotropy up to 5.4. These findings underscore the importance of integrating texture impact into glacier flow models, particularly in temperate environments where recrystallization and complex stress regimes prevail
Sulfur-Driven Cadmium Isotope Fractionation by Low-Molecular Weight Organic Ligands: Experimental Evidence from the Donnan Membrane Technique
No full textInternational audienceOrganic ligands have been suggested to play a key role in controlling the root-to-shoot transport and isotope fractionation of cadmium (Cd) in crops. In this work, we used the Donnan membrane technique to determine the Cd equilibrium isotope fractionation that is induced by the chelation of Cd with low-molecular weight organic ligands. While a model ligand with oxygen and nitrogen functional groups (EDTA, R-OH, R-NH) induced no significant isotope fractionation between complexed and free Cd 2+ (Δ 114/110 CdCdEDTA -freeCd = -0.08 ± 0.12‰, n = 4), the model ligand with sulfur donor groups (DMPS, R-SH) induced a strong isotope fractionation (Δ 114/110 CdCdDMPS -freeCd = -0.66 ± 0.20‰, n = 4). These experimental results indicate that binding of Cd to thiols plays a major role in retaining light Cd isotopes in roots and shoots, thereby minimizing transfer to cereal grains.Il a été suggéré que les ligands organiques jouent un rôle clé dans le contrôle du transport racine-pousse et du fractionnement isotopique du cadmium (Cd) dans les cultures. Dans le cadre de ces travaux, nous avons utilisé la technique de la membrane de Donnan pour déterminer le fractionnement isotopique à l'équilibre du Cd induit par la chélation du Cd avec des ligands organiques de faible poids moléculaire. Alors qu'un ligand modèle comportant des groupes fonctionnels oxygène et azote (EDTA, R-OH, R-NH) n'a induit aucun fractionnement isotopique significatif entre le Cd 2+ complexé et le Cd 2+ libre (Δ 114/110 CdCdEDTA -Cd libre = -0,08 ± 0,12 ‰, n = 4), le ligand modèle avec des groupes donneurs de soufre (DMPS, R-SH) a induit un fort fractionnement isotopique (Δ 114/110 CdCdDMPS -Cd libre = -0,66 ± 0,20 ‰, n = 4). Ces résultats expérimentaux indiquent que la liaison du Cd aux thiols joue un rôle majeur dans la rétention des isotopes légers du Cd dans les racines et les pousses, minimisant ainsi leur transfert vers les grains céréaliers
Characterization of the submarine disposal of a Bayer effluent (Gardanne alumina plant, southern France): V: Evolution of metal and metalloid concentrations in the seawater column of the discharge area (Mediterranean Sea) from 2016 to 2024
No full textInternational audienceThis study examined the evolution of trace metal and metalloid concentrations in the Cassidaigne canyon water column (Mediterranean Sea), at the Gardanne alumina plant discharge area, between 2016 and 2024. Following the 2015 ban on solid waste discharge, the plant progressively switched to the discharge at sea of a regulatory clarified effluent, resulting from filter-presses, CO 2 treatment and biological unit implementations. Several anomalies in element concentrations at discrete depths in the water column above the outfall (station L1) reflected local environmental influences, such as submarine groundwater discharges and lithogenic inputs, including mistral-induced upwelling, remobilizing sediment. From 2016 to 2021, Al concentrations below 200 m depth resulted from the effluent-seawater mixing (the plume) and subsequent metals and metalloids removal and/or release during hydrotalcite particles formation and dissolution. Concretions at the outfall of the effluent (330 m depth) stopped forming after introduction of the CO 2 treatment of the effluent in 2018. Despite occasional biological treatment disruptions leading to increased Al, V, and Cu concentrations at sea in 2020 and 2021, the effluent's chemical footprint remained globally confined in the first hundred meters above the outfall, without broader upper water column impact. Deep Al anomalies at a distant site (station K) in the canyon axis also indicated potential local remobilization from legacy bauxite deposits. Overall, both the plume and the historical residues appeared as localized but distinct sources of contamination. Particular renewed attention emerged from monitoring committees regarding ancient deposits, the spatial extent of which in the canyon far exceeds the chemical footprint of the effluent
Earth’s rotation perturbation by gravitational waves from compact binaries
No full textInternational audienceGravitational waves (GWs) are ripples in space-time that propagate deformations caused by compact bodies throughout the Universe. As an elastic body, the Earth responds to passing GWs much like a resonant sphere. This interaction produces a redistribution of mass, which results in perturbations of the Earth’s tensor of inertia. By conservation of angular momentum, such perturbations lead to a displacement of the rotation axis within the mantle (polar motion) and to changes in the spin rate, directly linked to variations in the length of day (LOD). In this work, we compute for the first time the perturbations of the Earth’s rotation induced by GWs emitted by compact white-dwarf binaries, using a normal mode summation approach applied to an elliptical, rotating, radially stratified Earth model. Our results indicate maximal amplitudes of approximately 10-15μs in the LOD and 10-15 mas for the polar motion—values that remain far below current instrumental sensitivities. These findings highlight the extreme difficulty of detecting GWs through their rotational effects on the Earth, yet the methodology developed here offers a framework that could be extended to other astrophysical bodies
Salinity Transition in the Ostia Lagoon During the Roman Period: Assessing the Feasibility of Salt Exploitation
No full textInternational audienceThis study examines long‐term salinity changes in the Ostia Lagoon between the 4th century cal BC and the 6th century cal AD , with emphasis on their implications for ancient salt production. Although Ostia's foundation is closely linked to the control of salt resources in the Tiber Delta, direct archaeological evidence of Roman‐period saltworks is scarce. To address this gap, this study combines micropalaeontological analysis of ostracod assemblages with a morphometric study of sieve pore features in Cyprideis torosa (Jones, 1850). This approach enables reconstruction of short‐term palaeosalinity dynamics. Core LOA–1 documents a transition from peatland to euryhaline lagoon between the 8th–6th and the 4th–3rd centuries cal BC , followed by repeated high‐salinity episodes. A notable peak coincides with the establishment of the Roman Castrum, suggesting favourable conditions for salt concentration. After the mid‐4th century cal BC , salinity peaks decreased, possibly reducing the lagoon's potential for saltworks and fostering greater reliance on the Maccarese saltworks. In the northern lagoon sector, hyperhaline conditions during the Roman period remain uncertain because of chronological gaps and the lack of sieve pore analysis. Overall, the results demonstrate both the potential and limitations of ostracod analysis as a palaeosalinity proxy and refine understanding of salt exploitation in the Tiber Delta. This study provides valuable insights into the long‐term socio‐environmental dynamics of the Mediterranean coastal wetlands, contributing to the advancement of geoarchaeological research on ancient salt production through salterns and its influence on human settlement patterns and economic practices
A parsimonious tail compliant multiscale statistical model for aggregated rainfall
No full textInternational audienceModeling rainfall intensity distributions across aggregation scales (from sub-hourly to weekly) is essential for hydrological risk analysis and IDF curves. Aggregation naturally imposes mathematical constraints: return levels must be ordered by time scale, as daily accumulations necessarily exceed sub-daily ones. From a statistical perspective, each aggregation step should ideally not require additional parameters, yet parsimonious models describing the full distribution remain scarce, as most literature focuses on seasonal block maxima. In this study, we propose a parsimonious framework to model all rainfall intensities (low to large) across scales. We utilize the Extended Generalized Pareto Distribution (EGPD), which aligns with extreme value theory for both tails while remaining flexible for the bulk of the distribution. We establish a general result on the behavior of EGPD variables under various aggregation procedures. To overcome the difficulty of direct likelihood inference, we link the EGPD class to Poisson compound sums. This allows the use of the Panjer algorithm for efficient composite likelihood evaluation. Our approach ensures that return levels do not cross across scales and enables estimation for return periods below annual or seasonal levels. We demonstrate the method using sub-hourly series from six French stations with diverse climates. Only eight parameters are needed per station to capture scales from six minutes to three days. IDF curves above and below the annual scale are provided
On the Application of <sup>238</sup>U, <sup>235</sup>U, and <sup>232</sup>Th Decay Series Disequilibria to Understanding the Processes and Timescales of Oceanic Basalt Petrogenesis
No full textInternational audienceUnderstanding how processes of magma genesis and magma differentiation control and modify the chemical composition of erupted lavas from the geochemical measurements of the latter is an under-constrained inverse problem, as there is only one known parameter—the measured composition of the erupted lava—but two unknown parameters—the chemical composition and lithology of the source before melting and how melting, crystallization, and melt–rock interactions act to alter the lava en route to the surface. In this invited contribution, we review nearly seven decades of scientific research that demonstrate the potential of U and Th decay series measurements for unraveling the complexities of oceanic magmatism. We review the underlying nuclear theory, geochemical principles, and application of the 238U, 235U, and 232Th decay series for (i) defining the timescales of magma genesis during decompression mantle melting, (ii) establishing the timescales of magma recharge and magma degassing, and (iii) determining the eruption ages of oceanic Quaternary volcanism
The ALPINE-CRISTAL-JWST Survey: JWST/IFU Optical Observations for 18 Main-sequence Galaxies at z = 4–6
No full textInternational audienceAbstract To fully characterize the formation and evolution of galaxies, we need to observe their stars, gas, and dust on resolved spatial scales. We present the ALPINE-CRISTAL-JWST survey, which combines kiloparsec-resolved imaging and spectroscopy from the Hubble Space Telescope, JWST, and Atacama Large Millimeter/submillimeter Array for 18 representative main-sequence galaxies at z = 4–6 and log ( M * / M ⊙ ) > 9.5 to study their star formation, chemical properties, and extended gas reservoirs. The cospatial measurements resolving the ionized gas, molecular gas, stars, and dust on 1–2 kpc scales make this a unique benchmark sample for the study of galaxy formation and evolution at z ∼ 5, connecting the Epoch of Reionization with the cosmic noon. In this paper, we outline the survey goals and sample selection, and present a summary of the available data for the 18 galaxies. In addition, we measure spatially integrated quantities (such as global gas metallicity), test different star formation rate indicators, and quantify the presence of H α halos. Our targeted galaxies are relatively metal rich (10%–70% solar), complementary to JWST samples at lower stellar mass, and there is broad agreement between different star formation indicators. One galaxy has the signature of an active galactic nuclei (AGN) based on its emission-line ratios. Six show broad H α emission suggesting type 1 AGN candidates. We conclude with an outlook on the exciting science that will be pursued with this unique sample in forthcoming papers
Contrasting roles of ground, trees, ponds and grazing in carbon dioxide, methane and nitrous oxide fluxes of an African semi-arid savanna
No full textInternational audienceUnderstanding greenhouse gas fluxes in semi-arid ecosystems is critical for improving our understanding ofbiogeochemical cycles, particularly in underrepresented regions like the African Sahel. In these landscapes,greenhouse gas exchange arises from ground, trees, and water ponds, and is further shaped by environmentalconditions and grazing. The carbon dioxide, methane, and nitrous oxide fluxes were quantified from thesecomponents in a Sahelian savanna in Senegal, while also assessing grazing impacts and environmental drivers(soil water content, temperature, vapor pressure deficit, photosynthetically active radiation). The ground was anet carbon dioxide sink during the rainy season but shifted toward neutrality or weak emission in the dry season,consistently acted as a methane sink, and was a year-round nitrous oxide source. Seasonal ponds were strongmethane and nitrous oxide emission hotspots, with methane emissions being high enough to offset the sink of theoverall savanna landscape. Trees contributed to carbon dioxide and methane uptake via branches, whereas stemswere net methane and carbon dioxide emitters. Both stems and branches emitted nitrous oxide, and the presenceof trees enhanced carbon dioxide, methane and nitrous oxide fluxes from soils beneath their canopies. Grazingenhanced ground gross primary production, reduced methane uptake, while no effect was seen on nitrous oxidefluxes. Temporal variability of carbon dioxide and nitrous oxide fluxes was strongly linked to soil water contentand temperature, whereas methane fluxes showed no correlations with any of the measured drivers. These resultsdemonstrate that tree- and pond-mediated fluxes, together with grazing, substantially alter the greenhouse gasfluxes of savanna ecosystems and incorporating these effects is essential for accurately representing semi-aridsavannas in global greenhouse gas budgets