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Mineral dust as a forcing factor behind primary productivity in the northwestern Arabian Sea since the Last Glacial Maximum
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Weakening of the Arctic Water Outflow From the Barents Sea and Consequences on the Fram Strait Warming
No full textInternational audienceAtlantic waters are transported to the Arctic Ocean mainly through the Fram Strait and the Barents Sea. Anomalous warm temperatures at the Fram Strait are generally interpreted as the consequence of a stronger and warmer West Spitsbergen Current (WSC) transporting the Atlantic Water (AW) northwards or as the propagation of warm anomalies across the Nordic Seas. In this study, we suggest that warm anomalies in the Fram Strait are also linked to a weakening of the westward flowing colder Arctic waters from the northern Barents Sea to the Svalbard region. Using a suite of satellite, in situ and reanalysis data, we propose two processes that could explain the weakening of this outflow during the recent decades. While direct wind forcing contributes to part of the observed weakening of the outflow, a reduction of the sea ice import from the central Arctic to the Barents Sea could impact the salinity in the northern Barents Sea, modify the meridional density gradient and further weaken the outflow. This phenomenon is eventually discussed in the context of long term trends and linked to the enhanced sea surface warming observed in the Fram Strait.Plain Language Summary An important part of the transport of warm and salty Atlantic Water to the Arctic Ocean occurs through the Fram Strait. Warm ocean anomalies in that region are generally interpreted as the consequence of a warmer and stronger current bringing more warm waters from the north Atlantic and the Nordic Seas. In this study, we suggest that colder waters exiting from the northern Barents Sea mix with Atlantic Waters before they reach the Fram Strait and that the weakening of the transport of this cold water input could be responsible for warm anomalies downstream. We propose that changes in the wind patterns could directly impact the outflow, but also reduce the sea ice and freshwater import from the central Arctic to the northern Barents Sea, which is expected to further reduce the intensity of the outflow. This mechanism could be linked to the accelerated warming observed in the Fram Strait region during the past decades.</p
Foraminiferal assemblages and organic matter relationships in a coastal lagoon on the arid coast of the Southeast Pacific
No full textInternational audienceThe Southeast Pacific arid zone, encompassing Peruvian and Chilean coastal deserts, features several wetlands that are influenced by upwelling waters and provide critical ecosystem services. Despite the significance of wetlands such as the coastal lagoon Poza La Arenilla (PLA) in Lima, Peru, their proximity to urban areas exposes them to eutrophication. This, in turn, presents considerable challenges for conservation efforts. Effective conservation strategies demand a comprehensive assessment of trophic conditions, achieved here by studying living and dead benthic foraminifera assemblages. These microorganisms serve as bioindicators for organic sources and enrichment. We explored their relationships with hydrological factors (dissolved oxygen, temperature, salinity) and sedimentary parameters (total organic matter, carbon, nitrogen, stable isotopes) in the PLA. Our results show that foraminifera distribution is influenced by organic matter (OM) from marine phytoplankton/algae and bacterial sources. Foraminifera were dominated by hyaline and soft-walled species, and 4 distinct foraminiferal assemblages were identified. Psammophaga sp1 prevailed in areas with abundant OM, while Bathysiphon sp. was associated with less organic conditions in sandy sediments. Additionally, Quinqueloculina seminulum , Buliminella elegantissima , Ammonia confertitesta , and Bathysiphon sp. were frequent and abundant species in the PLA. Dead assemblages showed a 2-fold increase in species richness compared to living foraminifera, indicating seasonal species turnover. Our study evidenced the importance of the whole diversity of foraminifera for environmental and/or ecological assessments, as groups of soft-walled and agglutinated foraminifera comprise potential bioindicators for eutrophication
Modelling oxidative potential of atmospheric particle: A 2-year study over France
No full textInternational audienceThe oxidative potential (OP) of particulate matter (PM) has emerged as a promising indicator of the adverse effects of PM on human health. In particular, OP is an indicator for oxidative stress in biological media through formation of reactive oxygen species. To provide a mapping of the spatial and temporal OP variability over France, we have developed a strategy to simulate the volume-normalized oxidative potential (OPv) in the state-of-the-art CHIMERE air quality model over the metropolitan French territory for the years 2013 and 2014. To do so, we combined a measurement-derived and source specific intrinsic OP (OPi) receptor modelling approach with Particle Source Apportionment Technology (PSAT) in CHIMERE. First, the model's ability to reproduce PM10 concentrations and speciation was verified using in situ observations in mainland France. Furthermore, a mostly satisfying correspondence between receptor model and PSAT outputs was obtained considering their source specific chemical profiles. Simulated versus observed OPv values showed median correlations ranging from 0.35 to 0.60 and mean fractional biases from −30 % to zero, depending on the OP assay considered (ascorbic acid AA, or dithiothreitol DTT) and the PM sources taken into account (i.e. two methods with different PM sources have been used, the reduced and the extended set methods). The modelled two-year average OPv fields show greater spatial hot spots over large urban areas (especially along roadsides) compared to those for PM10 distributions, due to elevated intrinsic OPi values for the primary anthropogenic sources such as traffic and biomass burning. These effects are stronger for the AA compared to the DTT assays, and for a method with a reduced set compared to an extended set of sources. Overall, through the OP apportionment, these results advocate for reinforcing action plans to reduce emissions from road traffic as well as biomass burning emissions
Methane (CH₄) Point Source Fine-Scale Modeling in the Aix-Marseille-Provence Metropolis Area, France
No full textInternational audienceThis study investigates methane (CH₄) emissions from point sources in the Aix-Marseille-Provence area, utilizing WindTrax 2.0 for fine-scale dispersion modeling. Datasets from sonic anemometers and line concentration sensors were integrated to simulate and predict CH₄ plume movements at wastewater treatment and industrial sites.The results highlight significant temporal variability in CH₄ emissions, with detailed visualizations identifying high-concentration zones. The findings highlight the utility of WindTrax 2.0 in understanding CH₄ dispersion, assisting in the development of more effective emission control strategies and regional environmental management
Pourquoi le record de températures en 2024 est une surprise pour les scientifiques
No full textInternational audiencePlus de 1,5 °C par rapport à l’ère préindustrielle : c’est l’augmentation moyenne des températures mesurées par les agences de surveillance du climat pour l’année 2024. Un record qui ne s’explique que partiellement par les activités humaines émettrices de gaz à effet de serre et que les scientifiques cherchent désormais à comprendre
Influence of the reproductive cycle and sex on microplastic toxicity in mussels
No full textInternational audiencePlastic contamination has become a major scientific and societal concern. While research on this issue has been flourishing over the last decade, several aspects remain insufficiently explored, including the chemical impact of plastic leachates (i.e., a complex mix of chemical compounds released by plastic particles). Furthermore, essential biological factors, such as the reproductive cycle and sex, are still largely overlooked, particularly in marine invertebrates, further limiting our ability to fully assess the ecotoxicological risks posed by pollutants. Here, we investigate the influence of these biological factors on organismal sensitivity to microplastic leachates (MPL) using two mussel species, Mytilus edulis and Mytilus galloprovincialis, which are important ecosystem engineers with significant economic values. The role of reproductive cycle was assessed in M. edulis through aggregation assays, while sex-based differences in sensitivity were assessed in M. galloprovincialis through byssal thread production assays. M. edulis showed increased sensitivity to MPL post-spawning, through a delay in their time to form their first aggregation, while female M. galloprovincialis showed higher sensitivity to MPL through increased byssal thread production. The observed effects may result from the high energetic cost of reproduction, coupled with potential endocrine-disrupting effects of plastic additives, highlighting the need for further studies. Our work stresses the importance of incorporating biological factors, such as the reproductive cycle and sex, into pollution risk assessments to enhance their ecological relevance.</div
Geomorphic consequences of freshwater discharge and microbial mats in a macrotidal environment: The case of the beach of Dannes (northern France)
No full textInternational audienceAbstract This study focuses on the geomorphic consequences of possible microbial mats associated with freshwater discharge on the macrotidal sandy beach of Dannes (northern France). The aim was to explain the lack of foredune at Dannes, in contrast to nearby beaches, despite similar sand resources and meteorological‐marine conditions. A transdisciplinary research was carried out, involving microbiology, geomorphology and sedimentology. In addition to topographic, hydrographic and sedimentological analyses related to the tidal cycle and storm occurrence, SEM analysis of the microtextures of quartz grains collected from the beach surface provided data on the marine and aeolian forces in the coastal system, as well as on the biological processes active in the sediment. The microbial composition of the beach surface sediment was identified using the metabarcoding approach with DNA extracted from samples collected in the field. The study highlights the presence of a millimetre layer of coloured sand that is strictly associated with freshwater outflows fed by groundwater from the Cretaceous Chalk aquifer. Several facts converge to identify this layer as a microbial mat where the aggregation of grains by bio‐mineralogical mechanisms stabilizes the beach surface. Although less than 50 m wide, and located in the supratidal beach, the microbial mats, which are constantly washed by freshwater, inhibit wind transport of sand and prevent foredune formation. On the other hand, they promote the formation of a berm in relation to the run‐up of storm waves, which could be enhanced by the low roughness of the microbial mat surface. Aerial photographs since 1946 show that the berm can form in less than 20 years, but it can suddenly disappear when the wave height and run‐up exceed the threshold that triggers berm erosion. Thus, physical and biological processes that are active on the supratidal beach interact to create distinctive landforms, i.e. berms instead of foredunes
Exploring coronal abundances of M dwarfs at moderate activity levels
No full textInternational audienceContext. Main sequence stars of spectral types F, G, and K with low to moderate activity levels exhibit a recognizable pattern known as the first ionization potential effect (FIP effect), where elements with lower first ionization potentials are more abundant in the stellar corona than in the photosphere. In contrast, high activity main sequence stars such as AB Dor (K0), active binaries, and M dwarfs exhibit an inverse pattern known as iFIP.Aims. We aim to determine whether or not the iFIP pattern persists in moderate-activity M dwarfs.Methods. We used XMM-Newton to observe the moderately active M dwarf HD 223889 that has an X-ray surface flux of log FX,surf = 5.26, the lowest for an M dwarf studied so far for coronal abundance patterns. We used low-resolution CCD spectra of the star to calculate the strength of the FIP effect quantified by the FIP bias (Fbias) to assess the persistence of the iFIP effect in M dwarfs.Results. Our findings reveal an iFIP effect similar to that of another moderately active binary star, GJ 338 AB, with a comparable error margin. The results hint at a possible plateau in the Teff -Fbias diagram for moderately active M dwarfs.Conclusions. Targeting stars with low coronal activity that have a coronal temperature between 2 MK and 4 MK is essential for refining our understanding of (i)FIP patterns and their causes
Tracing magnetic switchbacks to their source: An assessment of solar coronal jets as switchback precursors
No full textInternational audienceContext. The origin of large-amplitude magnetic field deflections in the solar wind, known as magnetic switchbacks, is still under debate. These structures, which are ubiquitous in the in situ observations made by Parker Solar Probe (PSP), likely have their seed in the lower solar corona, where small-scale energetic events driven by magnetic reconnection could provide conditions ripe for either direct or indirect generation.Aims. We investigated potential links between in situ measurements of switchbacks and eruptions originating from the clusters of small-scale solar coronal loops known as coronal bright points to establish whether these eruptions act as precursors to switchbacks.Methods. We traced solar wind switchbacks from PSP back to their source regions using the ballistic back-mapping and potential field source surface methods, and analyzed the influence of the source surface height and solar wind propagation velocity on magnetic connectivity. Using extreme ultraviolet images, we combined automated and visual approaches to identify small-scale eruptions (e.g., jets) in the source regions. The jet occurrence rate was then compared with the rate of switchbacks captured by PSP.Results. We find that the source region connected to the spacecraft varies significantly depending on the source surface height, which exceeds the expected dependence on the solar cycle and cannot be detected via polarity checks. For two corotation periods that are straightforwardly connected, we find a matching level of activity (jets and switchbacks), which is characterized by the hourly rate of events and depends on the size of the region connected to PSP. However, no correlation is found between the two time series of hourly event rates. Modeling constraints and the event selection may be the main limitations in the investigation of a possible correlation. Evolutionary phenomena occurring during the solar wind propagation may also influence our results. These results do not allow us to conclude that the jets are the main switchback precursors, nor do they rule out this hypothesis. They may also indicate that a wider range of dynamical phenomena are the precursors of switchbacks