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Lesser Antilles seismotectonic zoning model for seismic hazard assessment
No full textInternational audienceSubduction zones pose a considerable challenge within the realm of seismotectonics, owing to their fault and structure interactions. The Lesser Antilles arc is a good example of how these complexities impact seismic hazard studies with strong along-strike variations in tectonic, seismic, and volcanic activities. While these activities have generated significant damage, the 1839 and 1843 event characteristics (locations, depths, mechanisms, magnitudes) along with their potential implications for megathrust seismicity remain a subject of debate, in particular in the frame of low interseismic coupling. This study is grounded in the compilation of instrumental and historical seismicity and fault catalogs, complemented by analyses of focal mechanisms and rupture types as well as geodetic velocities and strain rates. The resulting seismotectonic zoning model of the Lesser Antilles encompasses the upper plate, subducting oceanic plate, subduction interface, mantle wedge, and volcanoes. We propose a better depth resolution, resulting from recent studies on slab top and upper-plate bottom geometries; a specific area source for the Marie-Galante graben; new propositions for mantle wedge and volcanic zoning; and fully revised area sources for the subduction interface. Our study highlights specific needs for a better seismic hazard assessment in this region
Une oasis dans un désert océanique
No full textLe long de l'arc volcanique des Tonga, au large de la Nouvelle-Calédonie, une zone très productive et importante pour la pêche a été identifiée dans le vaste désert océanique du Pacifique tropical. Un mystère éclairci grâce à une campagne océanographique
Water, Waterborne Pathogens and Public Health: Environmental Drivers. Report on an American Academy of Microbiology Colloquium held on Dec. 5 and 6, 2024 Washington (D.C.)
No full textInternational audienceHumans were once nomadic, constantly moving in search of resources. However, the Industrial Revolution marked a significant turning point. We chose to abandon our wandering ways and establish permanent settlements, creating communities designed to meet our diverse needs. Water, an elemental necessity for life, continued to be a crucial resource. Yet we failed to foresee how fluctuations in water availability would profoundly affect the ecology of environmentally sensitive pathogens, thereby impacting human health in unforeseen ways. This oversight has led to complex challenges in managing water resources and safeguarding public health functions. With more than 3.5 million deaths each year attributable to waterborne pathogens, it is a critical time to question our ability to understand the relationships between water and public health, particularly to the etiological pathways in which environmentally sensitive pathogens interact with human populations and have resulted in major pandemics of our times. We also need to provide introspection on the very basic tenet of life: is safe water a right or a privilege? This report seeks scientific scholarship and evidence to answer this question, with particular emphasis on waterborne pathogens as the key indicators of safe water available for humans. This report is based on the deliberations of experts who participated in a colloquium on December 5 and 6, 2024, organized by the American Academy of Microbiology, the honorific leadership group and think tank within the American Society for Microbiology (ASM), and the American Geophysical Union (AGU). These experts, from various fields and sectors, focused on how changes in water and the environment affect the spread of infectious diseases. They reviewed current knowledge and identified key gaps in understanding the relationship between water and disease-causing microorganisms in today's world. They identified several key issues to enhance public health.• Expand collaboration and engagement. Experts in earth sciences, microbiology, hydrology and public health along with community leaders need to collaborate.• Strengthen water systems. Modern and resilient water infrastructure allows for improved water safety, reduced disease risk and sustainable economic benefits.• Improve knowledge sharing. Integrate data systems that link Earth observationsand weather parameters with public health information for proactive public healthsupport
Pyrite morphology and sulfur isotopes refine taphonomic models for the 2.1 Ga Francevillian biota, Gabon
No full textInternational audiencePyritization is a key taphonomic process that preserves some of Earth's oldest fossils. It is influenced by various factors such as organic matter type, the availability of iron and sulfur, and sedimentation rates. In this study, we analyzed pyritized biotic and abiotic structures from 2.1 Ga deposits in Gabon's Francevillian Basin, to reconstruct their taphonomic pathway at the micron scale. Using secondary ion mass spectrometry and scanning electron microscopy, we examine sulfur isotope compositions, pyrite morphology and grain size within individual fossils and compare them to abiotic pyritic concretions from the same stratigraphic level. Our results reveal differences in pyrite grain size and sulfur isotope composition between fossils and concretions. More importantly, chemical and morphological variations are observed within individual fossils, likely due to distinct reactive environments for pyrite mineralization, linked to organic matter, sulfate and iron availability during early diagenesis. This remarkable variation in pyrite morphology and δ34S values in the fossilized specimens, indicates that they were compositionally more complex than the substrate that formed the homogeneously pyritized concretions. This well-preserved ecological window represents an exceptional record of the earliest multicellular life forms on Earth
Inventory of landslides affecting the coastal cliffs of Charente-Maritime (France): Typology, frequency, surface area and observation methods
No full textInternational audienceCharente-Maritime is a French department featuring 90 km of rocky coastline, of which 60 km remain unprotected by artificial longitudinal coastal defenses (Figure 1.A). The dynamics of these rocky coasts have been relatively understudied compared to other French regions, such as Normandy (Lissak et al., 2013; Letortu et al., 2014) or the Basque Country (Prémaillon, 2018; Martins et al., 2022; Guillen, 2024). As a result, the processes driving cliff retreat and coastal evolution in Charente-Maritime remain poorly understood, despite the fact that these cliffs represent a substantial portion of the department's coastline. Both human interests (e.g., coastal pathways, residential areas) and environmental priorities (e.g., sensitive natural habitats) are directly affected by the retreat of these rocky coasts. Without adequate adaptation to climate change, coastal erosion could endanger approximately 46.000 homes and 5.000 businesses along all types of coastlines in Charente-Maritime by 2100, with potential financial losses estimated at 15 billion euros (Hédou et al., 2024). In this context, it is crucial to identify rocky coastlines exposed to a high erosion hazard in order to implement appropriate coastal management and adaptation strategies.This study investigates the retreat mechanisms of the rocky coasts in Charente-Maritime through an inventory of landslides. It aims to address both scientific and methodological questions: (i) How are these rocky coasts retreating? (ii) What is the relationship between the frequency and the volumes of landslides? (iii) Which acquisition method — pedestrian surveys or drone-based inventories — proves to be the most comprehensive?Seven study sites were selected in Charente-Maritime based on their diverse geographical and geomorphological characteristics (Figure 1.A). Quarterly data acquisition was conducted through field surveys, complemented by drone surveys performed every six months. These two methods were selected for their ability to capture data over short time intervals and to detect landslides involving small volumes (≤ 10 m³). Since November 2023, five field surveys and two UAV (unmanned aerial vehicle) acquisitions have been conducted across all study sites. This approach has already documented hundreds of events, largely due to a succession of storms during the winter of 2023–2024 combined with very high tidal coefficients.According to the scientific literature (Sunamura, 1992; Dikau et al., 1996; Hungr et al., 2014), five main types of landslides responsible for the dismantling of the cliffs in Charente-Maritime have been identified: rockfall, rock topple, slide, flow, and debris flow. Initial results from surveys conducted between November 2023 and December 2024 reveal that rockfalls (x̄ = 15 m³) and debris flows (x̄ = 11 m³) are the most frequent modes of cliff retreat at the departmental scale, despite involving relatively small volumes due to the low height of the cliffs. At the scale of individual study sites, the hierarchy of processes varies depending on the specific characteristics of each site, with lithology playing a key role in determining the mechanisms of cliff dismantling.The statistical sample obtained from the inventory confirms that the rockfalls affecting the cliffs of Charente-Maritime are characterised by small volumes (x̄ = 17 m³; σ = 37.4 m³) but a high spatio-temporal frequency (about 20 rockfalls per kilometre per year). An initial assessment of the frequency/intensity relationship can be proposed at both the departmental and site-specific scales
CLIMAAX - Deliverable Phase 1 – Climate risk assessment
No full textRéunion Island’s Climate Risks Atlas project (RISC-RA) aims to carry out an assessment of climate risks on Réunion Island, a French overseas territory exposed to intense natural hazards. Réunion Island’s Regional council, hereafter called Region Réunion, a local public authority in charge of sustainable development and regional planning, has been managing the project since 1st October 2024 in collaboration with a scientific research group.This deliverable presents the organization, methodology and results of the RISC-RA project at the end of the first 6 months of work. The initial climate risks assessment has prioritized two main climate hazards: Droughts and Heavy Rainfall events, each already posing substantial and growing threats to socio-economic stability, infrastructure integrity, public health, and environmental sustainability. The general CLIMAAX methodology was adapted to the local context, using high-resolution climate data and local exposure and vulnerability datasets. The first phase of RISC-RA was also devoted to setting up the team's operational organization, establishing project governanceand making initial contacts with external stakeholders.Regarding the two main risks addressed during this phase, the following observations and results can be drawn:(1) Drought Risk: Droughts on Réunion Island are slow-onset hazard Island caused by prolonged periods of below-normal rainfall. The territory experienced extreme drought in December 2024 and January 2025, the driest months recorded for over 50 years. The analysis using regional climate projections indicates an increase in both intensity and spatial extent of drought risk, particularly in the northern and northwestern regions.(2) Extreme Rainfall Risk: the island holds most world records for rainfall duration over time intervals ranging from 12 hours (1144 mm) to 15 days (6083 mm). Heavy rainfall is a sudden-onset hazard expected to intensify, with projections indicating extreme rainfall events becoming more frequent, notably affecting northern, eastern, and southern coastal regions. Historical analysis identified a threshold of approximately 220 mm/day, regularly triggering catastrophic events.Phase 1 provided significant insights into regional climate vulnerabilities and risks, particularly highlighting drought and extreme rainfall as pressing concerns. This year 2025 was a perfect example of this, with a persistent heatwave during the first’s months, a severe drought in the northeastern areas, including water unavailability and water restrictions usages. This was followed by Cyclone Garance, one of the strongest cyclones experienced in La Reunion with devastating impacts.The climate risks analysis produced during phase 1 will serve as the first version of the Risk Atlas, which will be refined and discussed with local public authorities and practitioners. The findings of deliverable no. 1 will be used as the basis for the first local workshop to present the RISC-RA projectto local stakeholders, such as the Drought Committee, for example. The preliminary results for both historical data and projection will be improved in Phase 2 with case studies for the validation of vulnerability indicators and the extended analysis of heavy rainfall. At the same time, one or two new Workflow(s) will be explored
A 60-year atmospheric nitrate isotope record from a southeastern Greenland ice core with minimal postdepositional alteration
No full textInternational audienceStable isotopes of atmospheric nitrate (NO-3) are valuable tools for tracing nitrogen sources and processes; however, their signals in ice core records are often disrupted by postdepositional processes. The ice core from the southeastern Dome (SE-Dome) in Greenland is a potential record of variations in atmospheric chemistry that has experienced a lower postdepositional effect owing to a high accumulation rate (∼1 m water equivalent per year). Herein, we report 60-year (1959–2014) δ15N(NO) and Δ17O(NO-3) records from the SE-Dome ice core. The δ15N(NO-3) decreased from 1960 to 1974 and exhibited clear seasonal changes (high in summer and low in winter). The Δ17O(NO-3) did not exhibit any significant long-term trends, but it did contain seasonal patterns. The mass-weighted annual average of δ15N(NO-3) values in the SE-Dome core were 4.2±2.8 ‰ lower than those in the Greenland Summit ice core between 1959 and 2006. The TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow (TRANSITS) model under the SE-Dome condition estimated changes of only 0.9 ‰ for δ15N(NO-3) and −0.2 ‰ for Δ17O(NO-3) from the initial deposition. Although differences in the source of NO-3 cannot be discounted, the lower δ15N(NO-3) values observed at SE-Dome compared to Summit were likely due to reduced postdepositional alteration. Therefore, the SE-Dome ice core NO-3 record offers a precise reconstruction of nitrogen oxides (NOx) emissions from both North America and western Europe, as well as atmospheric oxidation chemistry and transport, thereby providing reliable insight into atmospheric nitrogen cycling
Large live biomass carbon losses from droughts in the northern temperate ecosystems during 2016-2022
No full textInternational audienceNorthern ecosystems (≥ 30°N) have been accumulating vegetation biomass carbon in recent decades, but increasing droughts and wildfires threaten this carbon sink. Here, we analyse annual changes in live vegetation biomass in northern ecosystems using low-frequency microwave satellite observations at 25 km spatial resolution from 2010 to 2022. We find that live biomass carbon stocks have undergone a reversal from a positive to a negative trend during the study period with 2016 marking the turning point. During 2016-2022, live biomass carbon stocks decreased at a rate of À0:20 À0:11 À0:26 PgC yr -1 across northern ecosystems, primarily in temperate biomes (À0:26 À0:17 À0:33 PgC yr -1 ). The annual mean gross loss of 4% of live biomass carbon in this region during 2016-2022 reflects high interannual variability, with significant losses associated with droughts and a further drop of À0:60 À0:47 À0:75 PgC in the very dry year of 2022. Our findings highlight the vulnerability of live biomass carbon stocks to emerging climate-induced disturbances in northern ecosystems, challenging the sustainability of the current large terrestrial carbon sink in this key region for the global carbon balance.Northern ecosystems (north of 30°N) hold about 41% of the world's forest area 1 , and are critical for mitigating global warming 2,3 , contributing an estimated 1.4-2.0 PgC annually to the global terrestrial carbon sink 4 . In recent decades, rising CO 2 levels and global warming have been reported to increase mid-and high-latitude vegetation productivity by lengthening the growing season 5 , which has resulted in a 'greening' trend as observed by optical satellite systems 6 . Concordantly, multiple lines of evidence from forest inventories 7,8 and satellite-based studies 9-11 suggest that biomass carbon has increased in northern ecosystems in recent decades.Climate hazards, however, may have affected the biomass carbon budget of northern ecosystems as a result of increased wildfire frequency 12 , extensive drought-induced tree mortality 13,14 and unprecedented scale of insect outbreaks 15 . Previous studies have indicated that threats to forest carbon sinks have increased in North America 16-18 and Europe 19-21 over recent decades due to tree mortality caused by very high temperatures and droughts. Wildfires, a main driver of Siberian and Canadian boreal forest disturbances, have been reported to cause large carbon emissions during recent extreme fire years 12,22 and have even led to parts of Siberia turning into a carbon source 13,23 . Compound droughtsheat waves (typically characterized by low soil moisture and high air temperatures) and wildfires have affected the northern Hemisphere in</div
Impact of environmental data on wind turbine noise level estimation
No full textInternational audienceWind energy is one of the most widely used renewable energy sources in the world and has grown rapidly in recent years. However, wind turbines generate noise that is often perceived as a disturbance by nearby residents. So, developing tools to assist wind farm developers and regulatory authorities is essential. This study focus on the impact of environmental data on wind turbine noise (WTN) level estimation using recurrent neural networks (RNNs). We compare the performance of an architecture which is based on long-short term memory cells (LSTM). LSTM model trained using only acoustic features in the frequency range of 31.5 Hz to 2 kHz with those incorporating additional environmental features, such as wind speed and wind turbine power accorded to each wind speed value. The results highlight the influence of these factors on noise characterization and demonstrate the extent to which environmental data enhances WTN level estimation
Raman lidar water vapor observations to assess the uncertainty of MLS and ERA5 at the upper troposhere
No full textInternational audienceWater vapor information in the upper troposphere (UT) is crucial for understanding the thermodynamic conditions leading to the formation of cirrus clouds and persistent contrails. Both phenomena significantly contribute to aviation-induced radiative forcing, driving global mitigation efforts. Raman lidars provide high-resolution humidity profiles, describing altitudes prone to ice supersaturation—conditions that are challenging to detect and accurately represent in current models.In this study, Raman lidar Water Vapor Mixing Ratio (WVMR) measurements from various sites in France were used to evaluate the performance of the ERA5 model in assessing humidity at typical aircraft altitudes. Additionally, the uncertainties in Microwave Limb Sounder (MLS) WVMR measurements at the same altitudes were assessed. Raman lidar profiles were aggregated into pseudo-monthly datasets to facilitate comparison with the limited number of MLS overpasses at each site, enabling validation of spatio-temporal pseudo-monthly lidar-matched MLS and ERA5 WVMR profiles.The MLS dataset offers one of the longest records of WVMR, making it a valuable resource for trend assessment. This investigation enables the validated use of these datasets for studying UT humidity trends and variability on seasonal and annual scales over the past decade