HAL-INSU
Not a member yet
203706 research outputs found
Sort by
Holocene microbialites from Lake Sevan (Armenia): sedimentary and geochemical archives of paleoenvironmental fluctuations
No full textInternational audienceOrgano-sedimentary structures, such as microbialites, are recognized as valuable records of past environmental conditions. However, their extreme sensitivity to even slight environmental changes give each microbialite highly specific sedimentary and geochemical characteristics, making it difficult to identify general features that could be associated with well-defined sets of past conditions. At Lake Sevan, in Armenia, Holocene microbialites have been discovered both along the shores and underwater, following a recent 20-meter drop in lake level. The exposed microbialites form linear arrangements at various altitudes, indicating former lake-level fluctuations. These structures thus provide a unique opportunity to explore the relationships between their sedimentary and geochemical features and the environmental settings in which they developed, as inferred from other proxies.Field, petrographic, and geochemical analyses (including isotopes, PLFAs, and alkanes) were carried out on both subaerial and submerged microbialites. Radiocarbon dating helped to place them within a chronological framework. In parallel, sedimentological and stratigraphic studies were conducted on outcrops, sections, and cores. These investigations enabled the construction of a high-resolution spatial and temporal framework, revealing multiple orders of lake-level fluctuations, some of which are interpreted as responses to tectonic events, including earthquakes.The microbialites were grouped based on their current altitude or depth, their age, and their position within lake-level fluctuation cycles. The sedimentary and geochemical features of each group were then compared to identify common traits that could be linked to specific paleoenvironmental conditions, as defined or described in the literature.This study identified the main environmental factors that influenced the formation, composition, and preservation of microbialites. It highlights that a thorough understanding of these complex yet invaluable natural archives requires extensive sampling and a detailed, multi-proxy analytical approach
Evolution of the South Pacific's Iron Cycle Over the Cenozoic
No full textInternational audienceAbstract Iron (Fe) availability impacts marine primary productivity, potentially influencing the efficiency of the biological carbon pump. Stable Fe isotope analysis has emerged as a tool to understand how Fe is sourced and cycled in the water column; however its application to sediment records is complicated by overlapping isotope signatures of different sources and uncertainties in establishing chronologies. To overcome these challenges, we integrate Fe and osmium isotope measurements with multi‐element geochemical analysis and statistical modeling. We apply this approach to reconstruct the history of Fe delivery to the South Pacific from three pelagic clay sequences spanning 93 million years. Our analysis reveals five principal Fe sources—dust, distal background, two distinct hydrothermal inputs, and a magnesium‐rich volcanic ash. Initially, hydrothermal inputs dominated Fe deposition, but as the sites migrated away from their respective mid‐ocean ridges, other sources became prominent. Notably, from 66 to 40 million years ago (Ma), distal background Fe was the primary source before a shift to increasing dust dominance around 30 Ma. This transition implies that Fe in South Pacific seawater has been dust‐dominated since ≈30 Ma, despite extremely low dust deposition rates today. We speculate that the shift to episodic and low Fe fluxes in the South Pacific and Southern Ocean over the Cenozoic helped shape an ecological niche that favored phytoplankton that adapted to these conditions, such as diatoms. Our analysis highlights how Fe delivery to the ocean is driven by large‐scale tectonic and climatic shifts, while also influencing climate through its integral role in marine phytoplankton and Earth's biogeochemical cycles
New Neandertal remains from Sirogne Cave (Lot, France): implications for human evolution and behavior prior to the last interglacial
No full textInternational audienceWhile neighboring regions have yielded numerous Neandertal remains, few discoveries have been reported from the limestone plateaus of the Quercy region in France [1]. However, the accidental discovery in 2006 of a Neandertal-like hemimandible and a deciduous tooth by a speleologist in Sirogne Cave — located within a Jurassic karst system in the northern part of the Alzou Canyon near Rocamadour (Lot, France) — prompted six excavation seasons between 2013 and 2018. These aimed to better understand the chronology, modes of Neandertal occupation, and biological evolution of the populations using the site.The excavations clarified the context of the 2006 discovery and revealed a partially disturbed stratigraphy, affected by recent human interventions. Nevertheless, several preserved layers, covered by stalagmitic floors along the western wall of the cave, were identified. Most notably, nearly 100 human fossils were unearthed from the cave, representing at least 10 individuals: Three children (aged 3–8 years), two adolescents, three young adults, and two older adults. The remains include two hemimandibles (one immature, one adult), over 80 isolated teeth, and infracranial elements. Although most come from sediments affected by post-depositional processes, all exhibit unambiguous Neandertal features. Several infracranial bones show cutmarks indicative of dismemberment and disarticulation, suggesting complex mortuary behaviors. The reworked layers also contained faunal remains from over 20 taxa, reflecting a broad but clearly Pleistocene spectrum resulting from both natural and anthropogenic accumulations. More than 2,000 lithic artefacts in quartz, flint, and limestone were also recovered, pointing to at least two Paleolithic techno-complexes: one attributed to the Middle Paleolithic and another to the end of the Last Glacial Maximum. Moreover, Sirogne may correspond to the “Crozo del Dua” cave excavated in the early 20th century by André Niederlander, which yielded five isolated Neandertal teeth and a lithic assemblage [1-3]. Our reanalysis of his faunal collectionled to the identification of two additional Neandertal remains — a phalanx and a lower permanent canine — morphologically consistent with the Sirogne material. Combined geological, taphonomic, biochronological, and absolute dating of the stalagmitic floors and associated sediments place the Neandertal fossils within Marine Isotope Stage (MIS) 6, most probably at the end of the Middle Pleistocene (ca. 150,000–130,000 years ago), which represents a critical, yet poorly documented, phase in Neandertal evolutionary history [4].Morphometric analyses of the teeth and mandibles suggest that the Sirogne individuals are more closely aligned with early Neandertals (pre-MIS 5) than with later groups. They exhibit classic Neandertal features and share affinities with Middle Pleistocene fossils based on external dental dimensions, enamel-dentine junction (EDJ) shape, and non-metric dental traits. Additionally, the low inter-individual variation in EDJ morphology indicates significant biological homogeneity within the Sirogne group. This homogeneity appears even greater than that observed at the Krapina MIS 5e site (Croatia), possibly reflecting regional isolation during MIS 6. Altogether, this exceptional assemblage offers rare and crucial insights into 18 population dynamics and evolutionary processes during a key period in Neandertal history. The evidence supports a model of strong group structuring and complex demographic patterns in Europe prior to 120,000 years ago [4]. Further analyses are currently underway, including attempts at ancient DNA extraction, calcium isotope studies for dietary reconstruction, and SR-microCT imaging of dental microstructures to explore growth patterns and developmental stress. A new three-year excavation project will further refine the chronocultural context and clarify the processes underlying the accumulation of human remains at the site
The Internal Waves Service Workshop: observing internal waves globally with Deep Learning and Synthetic Aperture Radar
No full textInternational audienceThe Internal Waves Service Workshop What: This workshop gathered leading experts in satellite remote sensing, oceanography, and artificial intelligence to advance the development of the Internal Waves Service (IWS)-the first global, operational platform for automatic detection of internal solitary waves (ISWs) from synthetic aperture radar (SAR) imagery. The participants reviewed the current state of internal wave research, shared technical advances, and defined priorities for future collaboration. When: 3-4 April 2025 Where: Angra do Hero & iacute;smo, Azores, Portuga
A colour code to raise public awareness of lithium resources
No full textInternational audienceThe supply of lithium to industry and its impact on the environment is a matter of growing public concern. Here, we propose a simple colour code to capture the diversity and characteristics of lithium resources in order to raise public awareness
Enhancing marine protected areas with effective ecological and environmental data integration
No full textInternational audienceMarine Protected Areas (MPAs) play a critical role in marine conservation, but their effectiveness, among other things, depends on robust ecological and environmental data integration. This paper explores key gaps and suggests ways forward for evaluating MPA ecological functionality, emphasizing the integration of species and habitat functional roles, process-based, and ecosystem-based indicators to assess species roles and ecosystem processes when identifying areas for conservation and supporting their management and governance. Connectivity is highlighted as a fundamental process, ensuring MPAs contribute to broader ecological coherence rather than acting as isolated spatial units. Given the dynamic nature of marine ecosystems, temporal adaptability, supported by long-term monitoring and data-driven decision-making, is essential for maintaining resilience amid climate change and anthropogenic pressures. Additionally, leveraging local and traditional knowledge through stakeholder engagement enhances MPA governance and implementation. By combining a diverse range of ecological indicators to aid decision-making, we can improve MPA effectiveness, ensuring they sustain biodiversity, ecosystem services, and resilience in the face of environmental change
Evaluer la participation : repères pour construire un protocole adapté
No full textÉvaluer un processus participatif est une démarche aussi nécessaire que complexe. Nécessaire, car elle permet d’analyser de manière rigoureuse comment un dispositif a été conçu et déployé (processus), ce qu’il a produit (résultats, effets, impacts), et ce que ces enseignements permettent d’améliorer ou de transformer. En ce sens, l’évaluation se définit comme un examen systématique et argumenté d’une action, visant à en apprécier la valeur au regard de qualités ou de principes explicites. Complexe, car chaque processus participatif est singulier : il s’inscrit dans un contexte spécifique, poursuit des intentions variées et mobilise des acteurs aux attentes multiples. Dans ce cadre, l’évaluation de la participation reste aujourd’hui limitée en quantité comme en qualité au regard des ambitions affichées de la participation. Elle se réduit souvent à des retours d’expérience partiels, à des analyses descriptives ou à l’usage parfois inadéquat de listes d’indicateurs génériques, qui peinent à rendre compte de la portée réelle des démarches.Ce document prend appui sur ce constat : l’évaluation ne peut pas se réduire à l’application mécanique de listes d’indicateurs préexistantes. Si elles constituent des ressources utiles, l’évaluation doit surtout être conçue comme un exercice réflexif et contextualisé, ajusté aux spécificités de chaque démarche. Plutôt qu’une méthode « clé en main », il s’agit ici d’accompagner la réflexion en identifiant les principales questions à se poser pour construire un protocole d’évaluation pertinent, qui invite à une démarche de clarification progressive, depuis les intentions du processus jusqu’aux choix méthodologiques
Influence des environnements vécus sur les perceptions des représentations des risques littoraux
No full textInternational audienc
Euclid preparation. Cosmology Likelihood for Observables in Euclid (CLOE). 3. Inference and Forecasts
No full textInternational audienceThe Euclid mission aims to measure the positions, shapes, and redshifts of over a billion galaxies to provide unprecedented constraints on the nature of dark matter and dark energy. Achieving this goal requires a continuous reassessment of the mission's scientific performance, particularly in terms of its ability to constrain cosmological parameters, as our understanding of how to model large-scale structure observables improves. In this study, we present the first scientific forecasts using CLOE (Cosmology Likelihood for Observables in Euclid), a dedicated Euclid cosmological pipeline developed to support this endeavour. Using advanced Bayesian inference techniques applied to synthetic Euclid-like data, we sample the posterior distribution of cosmological and nuisance parameters across a variety of cosmological models and Euclid primary probes: cosmic shear, angular photometric galaxy clustering, galaxy-galaxy lensing, and spectroscopic galaxy clustering. We validate the capability of CLOE to produce reliable cosmological forecasts, showcasing Euclid's potential to achieve a figure of merit for the dark energy parameters and exceeding 400 when combining all primary probes. Furthermore, we illustrate the behaviour of the posterior probability distribution of the parameters of interest given different priors and scale cuts. Finally, we emphasise the importance of addressing computational challenges, proposing further exploration of innovative data science techniques to efficiently navigate the Euclid high-dimensional parameter space in upcoming cosmological data releases