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Fifty shades of grayness: parameterizations of spectral distortions and applications in cosmology
No full textInternational audienceThermal distribution functions can only be of the Fermi-Dirac or Bose-Einstein types, whereas distorted spectra encompass any possible deviations from these shapes. It is fruitful to devise parameterizations of these distortions with only a few parameters which depend on the physical system considered. A method proposed by Stebbins consists in describing a distorted spectrum as a sum of thermalized spectra with a distribution of temperatures, the moments of which are the parameters of interest. After revisiting and extending this approach by working at the level of the number density distribution instead of the standard spectrum, we build another method which consists in describing the distorted spectrum by a polynomial modulating a reference thermalized spectrum. The distortion parameters are then the coefficients of a decomposition on a suitable orthonormal polynomial basis. We advocate that the latter is computationally easier and allows to describe a wide range of distortions. With this formalism, we efficiently describe the standard distortions of the cosmological backgrounds of neutrinos and photons, and we obtain model-independent constraints on nonstandard distortions of these cosmological relics
Rapport sur les services climatiques réussis dans le monde et leurs critères de succès: Livrable commun au Projet ciblé TRACCS-PC1-DIALOG (D5.3) et au Projet Ciblé TRACCS-PC3-DEMOCLIMA (D1)
No full textLes enjeux socio-économiques liés aux effets du réchauffement climatique sont tels qu’une demande croissante d’informations climatiques adaptées pour la mise en place de stratégies d’atténuation et/ou d’adaptation est clairement exprimée par les secteurs économiques (e.g. agriculture, énergie, tourisme, infrastructures terrestres ou maritimes, etc…) et par les territoires/régions qui mesurent pleinement leursvulnérabilités. En réponse à ces demandes, de nombreux projets de recherche nationaux (e.g., la "Convention relative à l’attribution d’un appui financier au bénéfice des services climatiques", signée entre le Ministère de la Transition Écologique et Solidaire (MTES) et le CNRS en mars 2017, ou le développement du portail DRIAS), européens (e.g., le programme ERA4CS « European Research Area for Climate Services » du JPI Climate, ou encore Copernicus) ou internationaux (e.g., les outils développés par la NASA, le GIEC…) ont permis le financement de « services climatiques ». Plusieurs acteurs opérationnels nationaux et européens développent et mettent à disposition des « services climatiques » via des plateformes souvent libres d’accès et enfin, apparaissent sur le marché des bureaux d’études dont l’activité commerciale vise le développement de « services climatiques » à la carte et adaptés aux demandes des clients.L’offre pour les « services climatiques » est donc aujourd’hui multiforme par l’information fournie (données climatiques « simples », indicateurs, outils d’aide à la décision) et par son mode de développement. Face à cette diversité, les enjeux sont de documenter et comprendre le paysage des services climatiques actuels, de faire ressortir les besoins, et de se munir de moyens pour caractériser la réussite des services climatiques, pour évaluer l'existant et guider le développement de nouveaux projets. Menée conjointement par les projets ciblés DIALOG (PC1) et DEMOCLIMA (PC3) du PEPR TRACCS, cette étude vise quatre objectifs :i) Documenter le paysage actuel des services climatiques (section 2) en France et dans le monde (identifiés par la communauté TRACCS) en les présentant par usages et cibles ;ii) Identifier des besoins non satisfaits vis-à-vis des services climatiques (section 4) ;iii) Identifier un ensemble de critères de réussite d'un service climatique pour les évaluer (section 5) ;iv) Proposer des bonnes pratiques pour atteindre ces critères de réussite (section 6); ces éléments guideront les choix des futurs démonstrateurs qui seront conçus et développés au sein de DEMOCLIMA.Notre travail repose en grande partie sur le recueil de dires d'acteurs des "services climatiques", dans une approche "bottom-up"
Distinct contributions of suspended and sinking prokaryotes to mesopelagic carbon budget
No full textInternational audienceThe mesopelagic zone, between 100 and 1000 meters depth, is a crucial layer, in which carbon preliminary coming down from the surface is transformed before a portion makes it into the deep ocean. While eddies and their fronts influence surface productivity and carbon export, their effects deeper in the water column remain poorly understood. Here we show the importance and contribution of dark carbon fixation—the conversion of inorganic into organic carbon by prokaryotes—across five contrasting hydrological features in the North Atlantic, using isotopic tracers and quantification of chemoautotrophy genes. The approach allows simultaneous assessment of dark carbon fixation and heterotrophic activity of prokaryotes living suspended in seawater and attached to gravitationally settling particles. Our results highlight that heterotrophic prokaryotes attached to sinking particles contribute up to 21% of the total organic carbon required to sustain prokaryotic metabolism under the influence of eddy fronts. In contrast, dark carbon fixation by suspended prokaryotes can contribute up to half of the total carbon input to the mesopelagic zone in the cyclonic eddy. Our findings challenge the idea that carbon cycling in the mid-depth ocean is uniform, and highlight the need to integrate microbial fractions and physical heterogeneity into ocean carbon model
Reimagining Urban River Bathing in Europe: A Multisectoral and Interdisciplinary Dive Into Lyon's Rivers (France)
No full textInternational audienceUrban river bathing is re‐emerging across Europe, driven by social demand and climate change impacts. The Urban Bathing Consortium, an interdisciplinary and intersectoral consortium initiated at the University of Lyon (France), is at the forefront of studying the challenges and opportunities of creating and managing healthy, safe, and accessible river bathing spaces. Through interdisciplinary collaboration among researchers and stakeholders, the consortium proposed an analytical framework, identifying seven critical dimensions for urban river bathing: the history and revival of city‐river relationships, legal and regulatory frameworks, bathing water quality, river drowning risks, river ecosystems, social perspectives, and urban planning. By examining these dimensions with state‐of‐the‐art approaches and drawing on Lyon's experiences, the study provides scientific insights and practical recommendations for future sustainable urban river bathing development. These include revitalizing historical city‐river connections, aligning local regulations with EU guidance, advancing holistic microbial water quality control, enhancing safety measures, incorporating ecological considerations, balancing competing river uses in urban planning, and addressing social needs for inclusive river governance
Assessment of surface water storage in the Amazon floodplains by hydrological modelling and earth observation data
No full textInternational audienceInland surface waters in tropical regions are fundamental to global hydrological and biogeochemical cycles, yet the quantification of floodplain freshwater storage and its variability remains limited. This study provides a basin-wide assessment of the spatiotemporal dynamics of floodplain water storage in the Amazon Basin over the period 2000-2018. We developed an integrated framework combining in situ discharge measurements, multisensor remote sensing datasets, and process-based hydrological modelling to quantify daily floodplain hydrodynamics at high spatial resolution. Floodplain extent was derived from L-band passive microwave observations from Soil Moisture and Ocean Salinity (SMOS) satellite, while water surface elevation was constrained using altimetry data (Jason-2/3 and Sentinel-3). The hydrological model (SWAF-FP), specifically improved to represent floodplain-river interactions, was calibrated at eight gauging stations and evaluated using approximately 4,000 altimetry-based floodplain water level records. Model performance demonstrated high skill, with a mean R2 of 0.83 for discharge and R2 > 0.62 for floodplain water surface elevation. The results indicate a mean annual surface water storage of 1800 +/- 854 km3 across the Amazon Basin, with pronounced seasonal cycles and interannual stability at the basin scale. The Negro and Madeira sub-basins were identified as the dominant contributors to total floodplain storage, accounting for approximately 480 km3 (33.6 %) and 312 km3 (12.5 %), respectively. This study provides the first consistent long-term quantification of Amazonian floodplain water storage dynamics at daily resolution. The results emphasize the critical role of floodplains in regulating basinscale hydrological fluxes and offer a robust observational-modeling framework for improving large-scale hydrological and Earth system models in tropical regions
Middle Eocene hyperthermal seasonality from Paris Basin marine mollusks
No full textInternational audienceThe Earth has experienced hyperthermal events in the past, characterized by maximum durations of hundreds thousand years, significant magnitude, global extent, and drivers associated with increases in greenhouse gas concentrations, therefore making them potential analogues for current climate change. The Middle Eocene Climatic Optimum (MECO) that occurred 40 Ma ago, is marked by a CO2-driven global warming of +4 to +6° C, affecting global temperatures. Here, we present a detailed reconstruction of seasonal fluctuations in seawater temperatures during this warming event in littoral environment, based on geochemical analyses (δ18O and Δ47) of shallow-marine mollusks from the Paris Basin. Our data show a stability in mean winter temperatures compared to pre-MECO conditions, but a marked warming of +10°C in maximum estuarine water temperatures, with a seasonal temperature range increasing from 12°C before the MECO to 22°C at the climax of the event. We demonstrate that at mid-latitudes, annual maximum shallow-water temperatures increased from 30 ± 2°C before the event to a maximum of 41 ± 4°C at the warming peak. This pattern is associated with a seasonal regime characterized by dry summers and wet winters, implying that the Paris Basin experienced a super-hot summer Mediterranean climate during the MECO
Microbial life in Arctic pack ice: Prospects for the Tara Polaris expeditions
No full textInternational audienceSea ice, unlike freshwater ice, hosts abundant microbial life, thanks to the presence of liquid water inclusions encased within the ice matrix. The forthcoming Tara Polaris Expeditions (TPE), which will document drifting Arctic pack ice repeatedly over multiple years, together offer an unprecedented opportunity to advance understanding of the sea-ice microbiome -its diversity, variations, and ecological roles. In this contribution, we consider the current state of knowledge, identify key research gaps, and outline the potential for progress enabled by TPE. We envision the emergence of new insights into the seasonal evolution of microbial life, resolved at the floe (kilometric) scale, in relation to the evolution of the sea-ice environment -its morphology, light, temperature, and liquid water distribution and properties. Large potential lies in the characterization of diverse microhabitats across the central Arctic Ocean, associated with brine inclusions, pressure ridge cavities, and melt ponds. A major goal will be to document biological processes that remain poorly understood -colonization, diversity, functioning, interactions, and evolutionary dynamics -and that could benefit from the application of newly developed techniques. We argue that TPE is particularly timely, as the loss of multi-year ice may soon constrain opportunities to study life in this rapidly changing habitat
The Synthetic Absorption Line Spectral Almanac (SALSA)
No full textInternational audienceWe create the first large-scale mock spectroscopic survey of gas absorption sightlines traversing the interstellar medium (ISM), circumgalactic medium (CGM), and intergalactic medium (IGM) surrounding galaxies of virtual Universes. That is, we create mock, or synthetic, absorption spectra by drawing lines-of-sight through cosmological hydrodynamical simulations, using a new mesh-free Voronoi ray-tracing algorithm. The result is the Synthetic Absorption Line Spectral Almanac (SALSA), which is publicly released on a feature-rich online science platform (www.tng-project.org/spectra). It spans a range of ions, transitions, instruments, observational characteristics, assumptions, redshifts, and simulations. These include, but are not limited to: (ions) HI, OI, CI, MgI, MgII, FeII, SiII, CaII, ZnII, SiIII, SiIV, NV, CII, CIV, OVI; (instruments) SDSS-BOSS, KECK-HIRES, UVES, COS, DESI, 4MOST, WEAVE, XSHOOTER; (model choices) with/without dust depletion, noise, quasar continua, foregrounds; (redshift) from z=0 to z~6; (ancillary data) integrated equivalent widths, column densities, distances and properties of nearby galaxies; (simulations) IllustrisTNG including TNG50, TNG-Cluster, EAGLE, and SIMBA. This scope is not fixed, and will grow and evolve with community interest and requests over time -- suggestions are welcome. The resulting dataset is generic and broadly applicable, enabling diverse science goals such as: (i) studies of the underlying physical gas structures giving rise to particular absorption signatures, (ii) galaxy-absorber and halo-absorber correlations, (iii) virtual surveys and survey strategy optimization, (iv) stacking experiments and the identification of faint absorption features, (v) assessment of data reduction methods and completeness calculations, (vi) inference of physical properties from observables, and (vii) apples-to-apples comparisons between simulations and data
BEES: Quasar lifetime measurements from extended rest-optical emission line nebulae at
No full textInternational audienceMeasurements of quasar lifetimes at high redshift indicate that the earliest billion-solar-mass supermassive black holes (SMBHs) have only been active as luminous quasars for less than a million years. Recently, extended Ly nebulae around quasars have revealed that these short observed lifetimes are unlikely a sightline-dependent effect. However, the interpretation of Ly emission is not straightforward due to its resonant nature. In this work, we use rest-frame optical emission lines, which more directly trace photoionization by the quasar, to unambiguously validate the short line-of-sight quasar lifetimes observed at early cosmic epochs. We use deep James Webb Space Telescope/NIRSpec IFU observations of five quasars with small proximity zones to search for their extended emission line nebulae in H and [O III], and detect extended emission in both emission lines around four quasars in our sample. We then use the light-crossing time of these nebulae to measure quasar lifetimes along transverse sightlines. Using their H nebulae, we also confirm that recombination is likely the dominant emission mechanism behind their previously detected Ly nebulae. Our results confirm the existence of high-redshift quasars with extremely short lifetimes, , hosting billion-solar-mass black holes, indicating that rapid accretion is likely responsible for the assembly of SMBHs in the early Universe
Mercury and other trace elements in gull chicks from a highly urbanised environment: effects on chick growth, physiology, and health condition
No full textInternational audienceCoastal urbanisation has increased the exposure of urban-dwelling organisms to contaminants, such as trace elements (TEs) in opportunistic seabirds. This exposure may cause detrimental health effects, especially during sensitive early life-stages, before detoxification mechanisms are fully developed. We monitored yellow-legged gull (Larus michahellis) chicks in the city of Porto, Portugal, and collected down feathers and blood for mercury (Hg) and other TE analyses. We aimed to i) evaluate the effects of maternal exposure to Hg (inferred from down feathers) on early chick development, and ii) examine the impact of blood TE contamination on chick physiology and health condition. Aligned with previous research, blood Hg decreased as chicks aged (up to the 5th week), due to the growth dilution effect and depuration into the growing feathers. Additionally, down feather Hg concentrations showed a limited transfer of Hg from females to the embryo and was unrelated to hatching mass or early growth rate. While low maternal Hg exposure resulted in no detectable effects on early-life development or chick survival, dietary exposure (inferred from blood) to other TEs incurred physiological costs. Blood arsenic (As) and lead (Pb) concentrations were associated with a faster erythrocyte sedimentation rate, suggesting impaired immune response and inflammation. This highlights a dichotomy between transgenerational Hg transfer and post-hatching dietary exposure to Hg and other TEs. Future work should aim to define toxicity thresholds for TEs in seabird chicks, investigating the implications in the health since early life stages, to better integrate the observed physiological responses