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Paleo-Scours Within the Layered Sulfate-Bearing Unit at Gale Crater, Mars: Evidence for Intense Wind Erosion
No full textInternational audienceThe surface of modern Mars is largely shaped by wind, but the influence of past wind activity is less well constrained. Sedimentary rocks exposed in the lower foothills of Aeolis Mons, the central mound within Gale crater, record a transition from predominantly lacustrine deposition in the Murray formation to aeolian deposition in the Mirador formation. Here, we report a series of enigmatic decameter-wide, concave-up scour-and-fill structures within the Mirador formation and discuss their formation mechanisms. Using panoramic images of stratigraphy exposed in cliff faces acquired by the Curiosity rover, we map the extent, distribution and orientation of the scour-and-fill structures and document the sedimentary facies within and surrounding these structures. The scours are grouped into two classes: (A) scours with a simple, symmetric morphology and light-toned, draping infill; and (B) scours with lateral pinching and dark-toned infill. We find that the scour-enclosing environment is composed of planar, even-in-thickness laminations with a pin-stripe pattern which we interpret as wind-ripple strata formed within an aeolian sandsheet environment. Class B contains cm-scale cross-bedding and a wing-shaped feature making this scour-and-fill structure consistent with fluvial processes. We interpret scour fill of class A as an aeolian infill due to similarities with the surrounding sandsheet strata. The broad morphologies and distribution of class A are also consistent with the geometry of blowout structures formed by localized, enhanced wind deflation. These paleo-blowout structures occur clustered within the same stratigraphic interval, which may imply that they record an interval of intensified wind activity at Gale crater
Comparaison de l'estimation de la chlorophylle par satellite et par BGC-Argo : une étude phénologique
No full textInternational audienceOcean primary production is a key process that regulates marine ecosystems and the global climate, but its estimation is still affected by multiple uncertainties. Typically, the chlorophyll-a concentration (CHL) is used to characterise this process, as it is considered as a proxy of phytoplankton biomass. To date, the most common observing systems for studying CHL are ocean colour satellites and Biogeochemical-Argo (BGC-Argo) floats. These are complementary systems: satellite observations provide global coverage but are limited to the ocean surface, while BGC-Argo floats provide punctual observations along the whole water column. Quantitative matching of these two observing systems has been obtained only at regional or single-float scales, while at a global scale the relatively low and irregular BGC-Argo coverage results in large uncertainties. Here, we propose a different method, by comparing satellite and BGC-Argo climatological annual time series within seven different bioregions, each characterised by a homogeneous phytoplankton phenology, allowing us to smooth the uncertainties. By comparing the mean values, amplitudes, and shapes of the two time series, we identify regions (a) where they agree (58%-61% of the ocean surface area); (b) regions undersampled by the BGC-Argo float network (particularly in the Arabian Sea and near the Amazon delta); (c) where the discrepancy may stem from satellite or (d) BGC-Argo performance (mainly found at subtropical and high latitudes, respectively). Caution is required when using BGC-Argo and satellite data in regions b-d, and, for each region, we provide suggestions on which system could be affected by the largest uncertainties
Source apportionment of organic gaseous and particulate compounds using a combined positive matrix factorization approach in summer (2020) in the Paris region (France)
No full textInternational audienceGaseous and particulate organic compounds are key components of atmospheric chemistry and better understanding their composition, sources and processes is essential to limit their impacts. Source apportionment using positive matrix factorization (PMF) is customarily performed for such studies. Combining organic aerosol data with their gaseous precursors was shown to be a promising approach, however very rarely attempted so far, to refine their origins using PMF. In this study, co-located continuous proton-transfer-reaction mass spectrometer (PTR-MS) and aerosol chemical speciation monitor (ACSM) measurements were performed at the suburban SIRTA station located in the Paris region. A combined dataset using both instruments during summer (June–August 2020) was then used in an exploratory PMF analysis to investigate the sources and processes of organic compounds, particularly the influences of biogenic emissions and important photochemical reactions on the formation of secondary organic aerosol (SOA) in this period of the year. Specific parameters and evaluation procedures were needed to ensure an equivalent representation of both instruments in the PMF model. A weighing factor was applied to the PTR-MS uncertainties which was controlled and optimized based on the analysis of the modelled scaled residuals. Seven main factors were obtained, describing anthropogenic sources (hydrocarbon-like organics, cooking-like organics), primary biogenic volatile organics, nighttime VOC, oxidized organics, aged organics and a specific isoprene oxidation factor which contributed 11 % to VOC and 4 % to OA. Compared to single-instrument PMFs, more factors were obtained, notably including the cooking-like factor which is not usually resolved using only ACSM data. This method also showed a better mathematical performance for the PTR-MS variables (mean absolute scaled residuals lower for the combined PMF (11.2) than for the PTR-MS-only PMF (38.2)) and a better separation of the factors for the ACSM variables in the combined PMF
Euclid preparation. Estimating galaxy physical properties using CatBoost chained regressors with attention
No full textInternational audienceEuclid will image ~14000 deg^2 of the extragalactic sky at visible and NIR wavelengths, providing a dataset of unprecedented size and richness that will facilitate a multitude of studies into the evolution of galaxies. In the vast majority of cases the main source of information will come from broad-band images and data products thereof. Therefore, there is a pressing need to identify or develop scalable yet reliable methodologies to estimate the redshift and physical properties of galaxies using broad-band photometry from Euclid, optionally including ground-based optical photometry also. To address this need, we present a novel method to estimate the redshift, stellar mass, star-formation rate, specific star-formation rate, E(B-V), and age of galaxies, using mock Euclid and ground-based photometry. The main novelty of our property-estimation pipeline is its use of the CatBoost implementation of gradient-boosted regression-trees, together with chained regression and an intelligent, automatic optimization of the training data. The pipeline also includes a computationally-efficient method to estimate prediction uncertainties, and, in the absence of ground-truth labels, provides accurate predictions for metrics of model performance up to z~2. We apply our pipeline to several datasets consisting of mock Euclid broad-band photometry and mock ground-based ugriz photometry, to evaluate the performance of our methodology for estimating the redshift and physical properties of galaxies detected in the Euclid Wide Survey. The quality of our photometric redshift and physical property estimates are highly competitive overall, validating our modeling approach. We find that the inclusion of ground-based optical photometry significantly improves the quality of the property estimation, highlighting the importance of combining Euclid data with ancillary ground-based optical data. (Abridged
The Unprecedented Late-Summer 2023 Heatwave in Southeastern South America: Attribution and future projection of similar events
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Cosmic reflections I: the structural diversity of simulated and observed low-mass galaxy analogues
No full textInternational audienceDwarf galaxies serve as powerful laboratories for investigating the underlying physics of galaxy evolution including the impact of baryonic feedback processes and environmental influences. We compare the visual and structural properties of dwarf galaxies in ultra-deep HSC-SSP imaging of the COSMOS field with those measured from realistic HSC-like synthetic observations of dwarfs generated by the Illustris TNG50 and NewHorizon simulations. Using Sérsic profile fitting and non-parametric morphological metrics (Gini, , asymmetry, and concentration), we evaluate the diversity of structural properties in observed and simulated galaxies. Our analysis shows that NewHorizon and TNG50 galaxies lie at opposite extremes of observed structural trends: NewHorizon produces diffuse, extended galaxies with shallow Sérsic indices, while TNG50 yields compact, concentrated systems with steep indices. Both simulations reproduce observed structural trends more closely at higher stellar masses () but fail to capture the full diversity of COSMOS dwarfs at lower masses. Non-parametric metrics further show that NewHorizon galaxies exhibit more uneven, clumpy light distributions while TNG50 galaxies have smoother but excessively concentrated profiles. These structural differences reflect underlying differences in their physical prescriptions and are likely driven by differing approaches to ISM physics, supernova feedback and star formation in addition to differences in numerical resolution. Our findings highlight the unique power of low-mass galaxies to constrain differences in simulation physics, especially star formation and feedback. Upcoming surveys from facilities like the Vera C. Rubin Observatory and Euclid will enable more rigorous comparisons with simulations, offering deeper insights into the physical processes shaping galaxy evolution
A multiplexing system for quantifying oxygen fractionation factors in closed chambers
No full textInternational audienceThe study of isotopic ratios of atmospheric oxygen in fossilized air trapped in ice core bubbles provides information on variations in the hydrological cycle at low latitudes and productivity in the past. However, to refine these interpretations, it is necessary to better quantify the fractionation of oxygen in biological processes such as photosynthesis and respiration. We set up a system of closed biological chambers in which we studied the evolution of the elemental and isotopic composition of O 2 due to biological processes. To easily replicate experiments, we developed a multiplexing system which we describe here. We compared measurements of the elemental and isotopic composition of O 2 using two different measurement techniques: optical spectrometry (optical-feedback cavity-enhanced absorption spectroscopy, i.e., OF-CEAS technique), which enables higher temporal resolution and continuous data collection, and isotopic ratio mass spectrometry (IRMS) with a flanged air recovery system, thus validating the data analysis conducted through the OF-CEAS technique. As a first application, we investigated isotopic discrimination during respiration and photosynthesis. We conducted a 5 d experiment using maize (Zea mays L.) as the model species. The 18 O discrimination value for maize during dark plant respiration was determined as -17.8 ± 0.9 ‰ by IRMS and -16.1 ± 1.1 ‰ by optical spectrometer. We also found a value attributed to the isotopic discrimination of terrestrial photosynthesis equal to +3.2 ± 2.6 ‰ and by IRMS and +6.7 ± 3.8 ‰ by optical spectrometry. These findings were consistent with a previous study by Paul et al. (2023).</div
Rapport de conjoncture 2024 de la Commission Interdisciplinaire (CID) 52 Environnement & Société : du Savoir à l'Action du Comité National de la Recherche Scientifique du CNRS
No full textThe environmental and societal challenges posed by climate change and the erosion of biodiversity raise the crucial question of our planet's short-term habitability. CID 52 Environments & Society : from knowledge to action develops a collective, interdisciplinary and concerted scientific approach to meet this challenge, by seeking innovative, inclusive methodologies and solutions that respect socio-ecosystems. Given the urgency of the situation, the commission stresses the need for scientists, decision-makers and citizens to work together to produce useful, transformative solutions for adapting societies to global change. These solutions explore social and technological change, as well as nature-based approaches. The report also highlights the importance of sustainable evaluation of solutions, while promoting interdisciplinarity as a response to global crises. CID 52 proposes to rename the commission Socio-ecosystems and the global environmental crisis: issues, knowledge and methodologies for sustainable solutions, better reflecting the integration of this research into public policy for effective and sustainable assimilation and adaptation of human and non-human populations.Les défis environnementaux et sociétaux associés au dérèglement climatique et à l'érosion de la biodiversité posent la question cruciale de l'habitabilité de notre planète à court terme. La CID 52 Environnements Sociétés : du savoir à l'action développe une approche scientifique collective, interdisciplinaire et concertée pour répondre à cet enjeu, en cherchant des méthodologies et des solutions innovantes, inclusives et respectueuses des socio-écosystèmes. Face à l'urgence de la situation, la commission insiste sur les nécessaires collaborations entre scientifiques, décideurs et citoyens pour coproduire des solutions utiles et transformantes d'adaptation des sociétés aux changements globaux. Ces solutions explorent ainsi les changements sociaux, technologiques et des approches fondées sur la nature. Le rapport met aussi en avant l'importance d'une évaluation durable des solutions, tout en promouvant l'interdisciplinarité pour répondre aux crises globales. La CID 52 propose de renommer la commission Socioécosystèmes et crise environnementale globale : enjeux, savoirs et méthodologies pour des solutions durables, reflétant mieux l'intégration de ces recherches dans les politiques publiques pour une assimilation et une adaptation efficace et durable des populations humaines et non-humaines.</div
Predicting individual’s decision to enter the water at a high-energy recreational surf beach in France
No full textInternational audienceObjectives To predict beachgoer decision to enter the water at a high-energy surf beach, in southwest France. Methods We built a unique multidisciplinary database combining data collected by an on-site beachgoers survey, weather stations, marine buoys and tidal reconstruction. Human, weather and meteocean factors were considered as potentially predictive of beachgoer behaviour. We employed a logistic regression analysis to predict beachgoers’ decision to enter the water on any given day at a high-energy recreational beach. Results We demonstrated that both environmental and human factors influence a beachgoer’s decision to enter the water. Daily mean wave height and daily mean insolation duration were significant predictors at the p<0.001 level, while age, place of residence and self-confidence in swimming out of a rip current were significant at the p<0.05 level or higher. Beachgoers were more likely to enter the water on sunny days with lower waves. Younger individuals, those living outside the Landes département, and those who declared themselves to be ‘confident’ or ‘uncertain’ about their ability to swim out of a rip current expressed a higher propensity to enter the water. Our model has an accuracy, F-Score, precision and recall of 71%, 73%, 86%, 79%, respectively. Conclusions Beachgoer exposure on any given day can ultimately be predicted by coupling our model with beach attendance models. This would allow for the design of rescue and preventive operations on days with high expected exposure. While models based solely on environmental factors can be used to forecast beach risks, incorporating human factors into the model provides valuable insight for crafting prevention messages. In this regard, lifeguards could engage more actively with beach users to deliver appropriate safety messages
Euclid : Early Release Observations – Deep anatomy of nearby galaxies
No full textInternational audienceEuclid is poised to make significant advances in the study of nearby galaxies in the Local Universe. Here we present a first look at six galaxies observed for the Nearby Galaxy Showcase as part of the Euclid Early Release Observations acquired between August and November, 2023. These targets, three dwarf galaxies (Holmberg II, IC 10, and NGC 6822) and three spirals (IC 342, NGC 2403, and NGC 6744), range in distance from about 0.5 Mpc to 8.8 Mpc. We first assess the surface brightness depths in the stacked Euclid images, and confirm previous estimates in 100 arcsec 2 regions for Visible Camera (VIS) of 1σ limits of 30.5 mag arcsec -2 , but find deeper than previous estimates for Near-Infrared Spectrometer and Photometer (NISP) with 1σ = 29.2-29.4mag arcsec -2 . By combining Euclid H E , Y E , and I E into RGB images, we illustrate the large field of view (FoV) covered by a single reference observing sequence (ROS), together with exquisite detail on scales of <1-4 parsecs in these nearby galaxies. Our analysis of radial surface brightness and color profiles demonstrates that the photometric calibration of Euclid is consistent with what is expected for galaxy colors according to stellar synthesis models. We perform standard source-selection techniques for stellar photometry, and find approximately 1.3 million stars across the six galaxy fields. After subtracting foreground stars and background galaxies, and applying a color and magnitude selection, we extract stellar populations of different ages for the six galaxies. The resolved stellar photometry obtained with Euclid allows us to constrain the star-formation histories of these galaxies, which we do by disentangling the distributions of young stars and asymptotic giant branch and red giant branch stellar populations. We finally examine two galaxies individually for surrounding systems of dwarf galaxy satellites and globular cluster populations. Our analysis of the ensemble of dwarf satellites around NGC 6744 recovers all the previously known dwarf satellites within the Euclid FoV, and also confirms the satellite nature of a previously identified candidate, dw1909m6341, a nucleated dwarf spheroidal at the end of a spiral arm. Our new census of the globular clusters around NGC 2403 yields nine new star-cluster candidates, eight of which exhibit colors indicative of evolved stellar populations. In summary, our first investigation of six “showcase” galaxies demonstrates that Euclid is a powerful probe of stellar structure and stellar populations in nearby galaxies, and will provide vastly improved statistics on dwarf satellite systems and extragalactic globular clusters in the local Universe, among many other exciting results