Modulation of the vertical particle transfer efficiency in the oxygen minimum zone off Peru
The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth's system. The OM produced through photosynthe-sis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive eastern boundary upwelling systems (EBUSs) associated with oxygen minimum zones (OMZs) would be expected to foster OM preservation due to low O 2 conditions. But their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru. Data provided high-temporal-resolution O 2 series charac-terising two seasonal steady states at the upper trap: sub-oxic ([O 2 ] < 25 µmol kg −1) and hypoxic-oxic (15 < [O 2 ] < 160 µmol kg −1) in austral summer and winter-spring, respectively. The OMZ vertical transfer efficiency of particulate organic carbon (POC) between traps (T eff) can be classi-Published by Copernicus Publications on behalf of the European Geosciences Union. 5094 M. Bretagnon et al.: Modulation of the vertical particle transfer efficiency fied into three main ranges (high, intermediate, low). These different T eff ranges suggest that both predominant preservation (high T eff > 50 %) and remineralisation (intermediate T eff 20 < 50 % or low T eff < 6 %) configurations can occur. An efficient OMZ vertical transfer (T eff > 50 %) has been reported in summer and winter associated with extreme limitation in O 2 concentrations or OM quantity for OM degradation. However, higher levels of O 2 or OM, or less refractory OM, at the oxycline, even in a co-limitation context, can decrease the OMZ transfer efficiency to below 50 %. This is especially true in summer during intraseasonal wind-driven oxygenation events. In late winter and early spring, high oxy-genation conditions together with high fluxes of sinking particles trigger a shutdown of the OMZ transfer (T eff < 6 %). Transfer efficiency of chemical elements composing the majority of the flux (nitrogen, phosphorus, silica, calcium car-bonate) follows the same trend as for carbon, with the lowest transfer level being in late winter and early spring. Regarding particulate isotopes, vertical transfer of δ 15 N suggests a complex pattern of 15 N impoverishment or enrichment according to T eff modulation. This sensitivity of OM to O 2 fluctuations and particle concentration calls for further investigation into OM and O 2-driven remineralisation processes. This should include consideration of the intermittent behaviour of OMZ towards OM demonstrated in past studies and climate projections .
(Biogeosciences. vol. 15, n° 1726-4170, pp. 5093-5111, 26/04/2026)
LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, LOV, INSU - CNRS, SU, CNRS, IMEV, INSU - CNRS, SU, CNRS, IMARPE, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, CAU, UABC, CICESE, IGP, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMARPE, IMAGO, INSU - CNRS, LOPS, IRD, IFREMER, INSU - CNRS, UBO EPE, CNRS
Ingestion and contact with polyethylene microplastics does not cause acute toxicity on marine zooplankton
Toxicity of polyethylene microplastics (PE-MP) of size ranges similar to their natural food to zooplanktonic organisms representative of the main taxa present in marine plankton, including rotifers, copepods, bivalves, echinoderms and fish, was evaluated. Early life stages (ELS) were prioritized as testing models in order to maximize sensitivity. Treatments included particles spiked with benzophenone-3 (BP-3), a hydrophobic organic chemical used in cosmetics with direct input in coastal areas. Despite documented ingestion of both virgin and BP-3 spiked microplastics no acute toxicity was found at loads orders of magnitude above environmentally relevant concentrations on any of the invertebrate models. In fish tests some effects, including premature or reduced hatching, were observed after 12 d exposure at 10 mg L-1 of BP-3 spiked PE-MP. The results obtained do not support environmentally relevant risk of microplastics on marine zooplankton. Similar approaches testing more hydrophobic chemicals with higher acute toxicity are needed before these conclusions could be extended to other organic pollutants common in marine ecosystems. Therefore, the replacement of these polymers in consumer products must be carefully considered.
(Journal of Hazardous Materials. vol. 360, n° 0304-3894, pp. 452-460, 26/04/2026)
IEO | CSIC, CSIC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GABI, INRA, IFREMER, UMR MARBEC, IRD, IFREMER, UM, CNRS, CNR
Qualité des Milieux Naturels
Qualité des Milieux Naturels
(pp. 96 p., 26/04/2026)
IC2MP [Poitiers], UP, INC-CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS, IPREM, UPPA, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IC2MP [Poitiers], UP, INC-CNRS, CNRS, P3F, INRA, ECOSYS, INRA
Les effets de la crue de juin 2016 sur la qualité de l'eau du bassin de la Seine
(26/04/2026)
GEOSCIENCES, PSL, METIS, EPHE, PSL, INSU - CNRS, SU, CNRS, GIP-Seine-Aval, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEESU, ENPC, UPEC UP12, GEDI, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LISIS, CNRS, INRAE
Towards the Development of a Storm Erosion EWS for the French Aquitaine Coast
Towards the development of a storm erosion EWS for the French Aquitanian coast. The 230-km long Aquitaine sandy coast, SW France, is vulnerable to erosion hazards owing to its full exposure to Atlantic storm waves. Since 2015, the Observatory of the Aquitaine Coast and several academic and local partners have developed a network to better survey and forecast storm-driven morphological changes at regional scale. This paper presents the implementation of an early warning system (EWS) with the primary objective to alert the network members 2-3 days ahead in order to perform pre-storm and post-storm surveys. Regional bulletins are edited to identify the most exposed coastal sections. At local scale, tests are realized on two morphological indicators used to forecast qualitatively and quantitatively the likelihood of beach and dune erosion. The two indicators (namely the Collision Regime Indicator, CRI, and the Eroded Volume Indicator, EVI, were calibrated and further validated at two nearby beaches where extensive morphological data are collected regularly: bimonthly surveys from 2009 to 2015 at Truc Vert beach and surveys every 2 to 7 days during the winters since 2015 at Biscarrosse beach. Results indicate promising performance, with the CRI predicting collision regime when front dune erosion was indeed observed, and the EVI predicting fairly accurate eroded sediment volume on cross shore beach profile. Nevertheless, more extensive validation of the CRI and EVI is needed to extend the indicators to the entire Aquitaine coast and for a wide range single storms and storm clusters.
(Journal of Coastal Research. vol. SI 85, n° 0749-0208, pp. 5 p., 26/04/2026)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Interaction of freshwater diatom with gold nanoparticles: adsorption, assimilation, and stabilization by cell exometabolites
The rising concern about the potential toxicity of synthetic gold nanoparticles (AuNPs) in aquatic environments requires a rigorous estimation of physico-chemical parameters of reactions between AuNPs and major freshwater microorganisms. This study addresses the interaction of 10-nm size, positively charged AuNPs with periphytic freshwater diatoms (Eolimna minima). The adsorption experiments on viable cells were performed in 10 mM NaCl and 5 mM NaCl + 5 mM NaHCO3 solution at a variable pH (3–10), at an AuNPs concentration from 1 µg/L to 10,000 µg/L, and an exposure time from a few minutes to 55 days. Three types of experiments, adsorption as a function of time (kinetics), pH-dependent adsorption edge, and constant-pH “Langmuirian” type isotherms, were conducted. In addition, long-term interactions (days to weeks) of live diatoms (under light and in the darkness) were performed. The adsorption was maximal at a pH from 3 to 6 and sizably decreased at a pH of 6 to 10. Results of adsorption experiments were modeled using a second order kinetic model, a Linear Programming Model, Freundlich isotherm, and a ligand binding equation for one site competition. The adsorption of AuNPs(+) most likely occurred on negatively-charged surface sites of diatom cell walls such as carboxylates or phosphorylates, similar to previously studied metal cations. Under light exposure, the AuNPs were stabilized in aqueous solution in the presence of live cells, probably due to the production of exometabolites by diatoms. The adsorbed amount of AuNPs decreased after several days of reaction, suggesting some AuNPs desorption. In the darkness, the adsorption and assimilation were stronger than under light. Overall, the behavior of positively charged AuNPs at the diatom–aqueous solution interface is similar to that of metal cations, but the affinity of aqueous AuNPs to cell exometabolites is higher, which leads to the stabilization of nanoparticles in solution in the presence of diatoms and their exudates. During photosynthetic activity and the pH rising above 9 in the vicinity of diatom cells, the adsorption of AuNPs strongly decreases, which indicates a decreasing potential toxicity of AuNPs for photosynthesizing cells. The present study demonstrates the efficiency of a thermodynamic and kinetic approach for understanding gold nanoparticles interaction with aquatic freshwater peryphytic microorganisms.
(Minerals. vol. 8, n° 2075-163X, pp. 99, 26/04/2026)
IOCAG, ULPGC, GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, TSU, FECIAR UrB RAS, RAS, IPGG SB RAS, SB RAS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ICMCB, UB, INC-CNRS, CNRS
Influence des conditions édaphiques sur la réponse des communautés alpines au changement global
Les effets du réchauffement climatique et de l'augmentation de la sécheresse estivale sur la composition et la diversité des communautés alpines ont été largement étudiés. Cependant le rôle modulateur des facteurs locaux tels que la roche mère, la mésotopographie et l'enneigement, est encore mal connu. Dans cette étude nous ré-échantillonnons la végétation d'un site de l'alpin inférieur des Alpes dauphinoises (France) étudié en 1997 et où se juxtaposent des variations importantes de roches mères (calcaire et siliceuse), de mésotopographie et d'enneigement susceptibles de moduler la réponse des communautés alpine au changement climatique. 112 relevés effectués en 1997 et 2017 et précisément géo-référencés, sont analysés par Analyse Factorielle des Correspondances. La végétation a très sensiblement évolué en 20 ans et montre une tendance vers la xérophilisation et l'oligotrophisation. La xérophilisation s'observe le long de l'axe 1 de l'AFC par déplacement de la position des relevés vers un pôle caractérisé par des sols superficiels calcaires à disponibilité en eau réduite, qui s'oppose à un autre pôle représenté par des sols acides développés sur roche siliceuse ou sur matériau mixte. Cet effet est particulièrement sensible au milieu du gradient de disponibilité en eau, en bordure de combes à neige. L'oligotrophisation, est probablement due à une baisse du pâturage et s'observe principalement le long de l'axe 2 de l'AFC, par déplacement de la position des relevés vers un pôle caractérisé par des sites exposés à déneigement précoce (mésotopographie convexe) sur sols siliceux. La richesse spécifique de l'ensemble des communautés décroit en moyenne de 15%, très probablement sous l'effet de l'augmentation de la compétition par les ligneux induite par la baisse du pâturage. Nos résultats montrent que les facteurs édaphiques locaux peuvent limiter la remontée altitudinale des espèces telle qu'elle est prédite par les principaux modèles de niche, la plupart des espèces pouvant trouver à la même altitude des refuges microclimatiques leur permettant d'éviter les effets du changement climatique.
(Botany / Botanique. vol. 4, n° 1916-2790, pp. 81-91, 26/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UB, UR LESSEM, IRSTEA, UGA [2016-2019], Fédération OSUG, UGA [2016-2019], LECA, USMB [Université de Savoie] [Université de Chambéry], CNRS, UGA [2016-2019]
The influence of natural dissolved organic matter on herbicide toxicity to marine microalgae is species-dependent
Microalgae, which are the foundation of aquatic food webs, may be the indirect target of herbicides used for agricultural and urban applications. Microalgae also interact with other compounds from their environment, such as natural dissolved organic matter (DOM), which can itself interact with herbicides. This study aimed to evaluate the influence of natural DOM on the toxicity of three herbicides (diuron, irgarol and S-metolachlor), singly and in ternary mixtures, to two marine microalgae, Chaetoceros calcitrans and Tetraselmis suecica, in monospecific, non-axenic cultures. Effects on growth, photosynthetic efficiency (Ф’M) and relative lipid content were evaluated. The chemical environment (herbicide and nutrient concentrations, dissolved organic carbon and DOM optical properties) was also monitored to assess any changes during the experiments. The results show that, without DOM, the highest irgarol concentration (I0.5: 0.5 mg.L−1) and the strongest mixture (M2: irgarol 0.5 μg.L−1 + diuron 0.5 μg.L−1 + S-metolachlor 5.0 μg.L−1) significantly decreased all parameters for both species. Similar impacts were induced by I0.5 and M2 in C. calcitrans (around −56% for growth, −50% for relative lipid content and −28% for Ф’M), but a significantly higher toxicity of M2 was observed in T. suecica (−56% and −62% with I0.5 and M2 for growth, respectively), suggesting a possible interaction between molecules. With DOM added to the culture media, a significant inhibition of these three parameters was also observed with I0.5 and M2 for both species. Furthermore, DOM modulated herbicide toxicity, which was decreased for C. calcitrans (−51% growth at I0.5 and M2) and increased for T. suecica (-64% and −75% growth at I0.5 and M2, respectively). In addition to the direct and/or indirect (via their associated bacteria) use of molecules present in natural DOM, the characterization of the chemical environment showed that the toxic effects observed on microalgae were accompanied by modifications of DOM composition and the quantity of dissolved organic carbon excreted and/or secreted by microorganisms. This toxicity modulation in presence of DOM could be explained by (i) the modification of herbicide bioavailability, (ii) a difference in cell wall composition between the two species, and/or (iii) a higher detoxification capacity of C. calcitrans by the use of molecules contained in DOM. This study therefore demonstrated, for the first time, the major modulating role of natural DOM on the toxicity of herbicides to marine microalgae.
(Aquatic Toxicology. vol. 198, n° 0166-445X, pp. 103-117, 26/04/2026)
UR EABX, IRSTEA, BE, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPM
Updated calibration of the clumped isotope thermometer in planktonic and benthic foraminifera
Accurate reconstruction of past ocean temperatures is of critical importance to paleoclimatology. Carbonate clumped isotope thermometry (“Δ47 ”) is a relatively recent technique based on the strong relationship between calcification temperature and the statistical excess of 13C–18O bonds in carbonates. Its application to foraminifera holds great scientific potential, particularly because Δ47 paleotemperature reconstructions do not require assumptions regarding the 18O composition of seawater. However there are still relatively few published observations investigating the potential influence of parameters such as salinity or foraminiferal size and species. We present a new calibration data set based on 234 replicate analyses of 9 planktonic and 2 benthic species of foraminifera collected from recent core-top sediments, with calcification temperatures ranging from −2 to 25 °C. We observe a strong relationship between Δ47 values and independent, oxygen-18 estimates of calcification temperatures:
Δ47 = 41.63 × 103/T2 + 0.2056
The formal precision of this regression (± 0.7–1.0 °C at 95 % confidence level) is much smaller than typical analytical errors. Our observations confirm the absence of significant species-specific biases or salinity effects. We also investigate potential foraminifer size effects between 200 and > 560 μm in 6 species, and conclude that all size fractions from a given core-top location and species display statistically undistinguishable Δ47 values. These findings provide a robust foundation for future inter-laboratories comparisons and paleoceanographic applications.
(Geochimica et Cosmochimica Acta. vol. 239, n° 0016-7037, pp. 1-16, 26/04/2026)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, CLIMAG, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
A comparison between water circulation and terrestrially-driven dissolved silica fluxes to the Mediterranean Sea traced using radium isotopes
The circulation of seawater through permeable coastal sediments is increasingly recognized as an important source of nutrients, including dissolved silica (DSi), to the coastal ocean. Here, we utilized a Ra isotope (223 Ra, 224 Ra ex , 228 Ra) mass balance to quantify DSi fluxes driven by water circulation to a small shallow coastal lagoon (La Palme; French Mediter-ranean) during June 2016, as compared to karstic groundwater spring inputs. The DSi flux driven by lagoon water circulation (derived from 224 Ra ex) was approximately one order of magnitude greater (1900 ± 1700 mol d À1) than the DSi load of the karstic groundwater spring (250 ± 50 mol d À1) and greater than molecular diffusion (970 ± 750 mol d À1). Lagoon water circulation was a negligible source of 228 Ra, indicating that circulation-driven DSi inputs occur over a timescale of days. Offshore transects were studied to quantify fluxes of marine-derived submarine groundwater discharge (SGD) from the permeable sandy coastline adjacent to the lagoon, into the Mediterranean Sea. Surface water transects revealed near-shore enrichments of Ra and DSi, attributed to wave-setup and water exchange through the permeable beach between the lagoon and the sea. Upscaling over the 9.5 km stretch of sandy beaches results in a marine SGD-driven DSi flux of 2.3 ± 1.3 Â 10 4 mol d À1 , similar in magnitude to the Têt river during November 2016 (3.3 ± 2.4 Â 10 4 mol d À1), the largest river in the region. A positive relationship between DSi and 224 Ra ex in lagoon water and seawater, but not 228 Ra, suggests that 224 Ra ex and DSi enrichments are derived from a similar source, the sediment (i.e. lithogenic particle dissolution), operating on short timescales. A marine SGD-driven DSi flux to the Gulf of Lions (3.8 ± 2.2 Â 10 5 mol d À1) is likely continuous over time. The relatively constant DSi inputs from water circulation for the shallow lagoons and beaches along the French Mediterranean Sea
(Geochimica et Cosmochimica Acta. vol. 238, n° 0016-7037, pp. 496-515, 26/04/2026)
LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, UAB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOMIC, INSU - CNRS, SU, CNRS, OOB, SU, CNRS, GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, JCU, VUB