Vulnerability of early developmental stages of the endangered species Acipenser sturio to pollution and global warming
European sturgeon (Acipenser sturio) is an anadromous fish which has been in sharp decline since the beginning of the 20th century. The last wild population of European sturgeon is settled in the Gironde Garonne Dordogne catchment. Because of global change, temperatures have risen and frequency and severity of hypoxic events have increased in this catchment. In addition, the A. sturio population faces chronic pollutant exposure due to increasing agricultural, industrial and domestic releases. The goal of this work is to examine the sensitivity of A. sturio early developmental stages to temperature variations, oxygen depletion and pollutions in environmentally realistic exposure conditions. Embryo-larvae were exposed to combined temperature conditions, ranged from 12°C to 30°C, and dissolved oxygen, ranged from 30 to 90 % O2 saturation (% O2 sat) and to four natural spawning grounds sediments. Lethal and sub-lethal effects were evaluated using embryonic and larval mortality, hatching success, malformation rate, yolk sac resorption, tissue development, routine metabolic rate (RMR), swimming speed and DNA damage (only for sediment exposure). Embryonic survival peaked at 20°C and no survival was recorded at 30°C. No hatching occurred at 50 % O2 sat or below. Malformation rate appeared to be minimum at 20°C and 90 % O2 sat. Maximum RMR were recorded at 20°C under 90 % O2 sat and at 16°C under 70 % O2 sat. At 20°C, RMR was lower at 70% O2 sat than at 90% O2 sat. Swimming speed peaked at 16°C. A. sturio's temperature optimum was shown to be close to 20°C. Its upper tolerance limit is between 26 and 30°C. Its lower tolerance limit was not reached and is supposed to be below 12°C. Oxygen depletion induce sublethal effects at 70 % and lethal effects at 50 % O2 sat. Strikingly, sediment quality of spawning ground had no effect on embryo-larval survival and hatching success. A significant increase of developmental defects and percentage of apoptotic cells was observed for one of the studied sediment. Current temperature, oxygen and sediment quality conditions in the Gironde basin are globally sustainable for A. sturio but a slight O2 levels decrease would impair European sturgeon maintenance capacity in the basin.
(pp. 21, 23/04/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, INRA
Evidence for the non-influence of salinity variability on the Porites coral Sr/Ca palaeothermometer
Porites coral-based sea surface temperature (SST) reconstructions are obtained from the measurement of skeleton Sr/Ca ratio. However, the influence of salinity in the incorporation of these trace elements in the Porites aragonitic skeleton is still poorly documented. Laboratory experiments indicate that in three different coral species (not including the widely used Porites genus), salinity does not influence the Sr/Ca thermometer. In this study, we test the salinity effect on Porites Sr/Ca-based SST reconstructions at monthly and interannual timescales in open-ocean environmental conditions. We use a large spatial compilation of published Porites data from the Red Sea and Pacific and Indian oceans. Additionally to those published records, we add a new eastern Pacific coral Sr/Ca record from Clipperton Atoll.Using two different salinity products (Simple Ocean Data Assimilation (SODA) SSS reanalyses version 2.2.4, Carton and Giese, 2008; and instrumental SSS from the Institut de Recherche pour le Développement, France (IRD) Delcroix et al., 2011), we find no evidence of salinity bias on the Sr/Ca SST proxy at monthly and interannual timescales. We conclude that Porites Sr/Ca is a reliable palaeothermometer that is not influenced by salinity variability.
(Climate of the Past Discussions [Climate of the Past Preprints]. vol. 11, n° 1814-9340, pp. 523-532, 23/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LDEO, BTP, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS
On the reduced sensitivity of the Atlantic overturning to Greenland ice sheet melting in projections: a multi-model assessment
(Climate Dynamics. vol. 44, n° 0930-7575, pp. 3261 - 3279, 23/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, MPI-M, DMI, MOHC, NERSC, PARVATI, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS
Phytoplankton versus macrophyte contribution to primary production and biogeochemical cycles of a coastal mesotidal system. A modelling approach
This study presents an assessment of the contributions of various primary producers to the global annual production and N/P cycles of a coastal system, namely the Arcachon Bay, by means of a numerical model. This 3D model fully couples hydrodynamic with ecological processes and simulates nitrogen, silicon and phosphorus cycles as well as phytoplankton, macroalgae and seagrasses. Total annual production rates for the different components were calculated for different years (2005, 2007 and 2009) during a time period of drastic reduction in seagrass beds since 2005. The total demand of nitrogen and phosphorus was also calculated and discussed with regards to the riverine inputs. Moreover, this study presents the first estimation of particulate organic carbon export to the adjacent open ocean.
The calculated annual net production for the Arcachon Bay (except microphytobenthos, not included in the model) ranges between 22,850 and 35,300 tons of carbon. The main producers are seagrasses in all the years considered with a contribution ranging from 56% to 81% of global production. According to our model, the -30% reduction in seagrass bed surface between 2005 and 2007, led to an approximate 55% reduction in seagrass production, while during the same period of time, macroalgae and phytoplankton enhanced their productions by about +83% and +46% respectively. Nonetheless, the phytoplankton production remains about eightfold higher than the macroalgae production. Our results also highlight the importance of remineralisation inside the Bay, since riverine inputs only fulfill at maximum 73% nitrogen and 13% phosphorus demands during the years 2005, 2007 and 2009. Calculated advection allowed a rough estimate of the organic matter export: about 10% of the total production in the bay was exported, originating mainly from the seagrass compartment, since most of the labile organic matter was remineralised inside the bay.(Estuarine, Coastal and Shelf Science. vol. 165, n° 0272-7714, pp. 52-60, 23/04/2026)
IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Glacial ice and atmospheric forcing on the Mertz Glacier Polynya over the past 250 years
The Mertz Glacier Polynya off George V Land, East Antarctica, is a source of Adélie Land Bottom Water, which contributes up to B25% of the Antarctic Bottom Water. This major polynya is closely linked to the presence of the Mertz Glacier Tongue that traps pack ice upstream. In 2010, the Mertz Glacier calved a massive iceberg, deeply impacting local sea ice conditions and dense shelf water formation. Here we provide the first detailed 250-year long reconstruction of local sea ice and bottom water conditions. Spectral analysis of the data sets reveals large and abrupt changes in sea surface and bottom water conditions with a B70-year cyclicity, associated with the Mertz Glacier Tongue calving and regrowth dynamics. Geological data and atmospheric reanalysis, however, suggest that sea ice conditions in the polynya were also very sensitive to changes in surface winds in relation to the recent intensification of the Southern Annular Mode.
(Nature Communications. vol. 6, n° 2041-1723, pp. 6642, 23/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULaval, INSU - CNRS, CNRS, LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, VOG, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, BTP, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS
The coccolithophores Emiliania huxleyi and Coccolithus pelagicus: Extant populations from the Norwegian–Iceland Seas and Fram Strait
The distributions of the coccolithophore species Emiliania huxleyi and Coccolithus pelagicus (heterococcolith-bearing phase) in the northern North Atlantic were investigated along two zonal transects crossing Fram Strait and the Norwegian–Iceland Sea, respectively, each conducted during both July 2011 and September–October 2007. Remote-sensing images as well as CTD and ARGO profiles were used to constrain the physico-chemical state of the surface water and surface mixed layer at the time of sampling. Strong seasonal differences in bulk coccolithophore standing stocks characterized the northern and southern transects, where the maximum values of 53×103 cells/l (fall) and 70×103 cells/l (summer), respectively, were essentially explained by E. huxleyi. This pattern confirms previous findings of a summer to fall northwestward shift in peak coccolithophore cell densities within the Nordic Seas. While depicting an overall zonal shift in high cell densities between the summer (Norwegian Sea) and fall (northern Iceland Sea) conditions, the southern transects were additionally characterized by local peak coccolithophore concentrations associated with a geographically and temporally restricted convective process (Lofoten Gyre, summer), as well as an island mass effect (in the vicinity of Jan Mayen Island, fall). Maximum coccolithophore abundances within Fram Strait were found during both seasons close to the western frontal zone (Polar and Arctic Fronts) an area of strong density gradients where physical and chemical properties of the surface mixed layer are prone to enhance phytoplankton biomass and productivity. Here, changes in species dominance from E. huxleyi in summer, to C. pelagicus in fall, were related to the strengthened influence during summer, of surface AW, as well as to high July solar irradiance, within an area usually characterized by C. pelagicus-dominated low density populations.
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 98, n° 0967-0637, pp. 1-9, 23/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UiT
Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions
While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood. Here we show that the subset of CMIP5 historical climate simulations that produce such bidecadal variability exhibits a robust synchronization, with a maximum in Atlantic Meridional Overturning Circulation (AMOC) 15 years after the 1963 Agung eruption. The mechanisms at play involve salinity advection from the Arctic and explain the timing of Great Salinity Anomalies observed in the 1970s and the 1990s. Simulations, as well as Greenland and Iceland paleoclimate records, indicate that coherent bidecadal cycles were excited following five Agung-like volcanic eruptions of the last millennium. Climate simulations and a conceptual model reveal that destructive interference caused by the Pinatubo 1991 eruption may have damped the observed decreasing trend of the AMOC in the 2000s. Our results imply a long-lasting climatic impact and predictability following the next Agung-like eruption.
(Nature Communications. vol. 6, n° 2041-1723, pp. 6545, 23/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, PARVATI, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CNRM, INSU - CNRS, CNRS, Comue de Toulouse
Carbon fixation and emission within dense aquatic weed mats of a temperate shallow lake
Dense aquatic weed mats are likely to enhance oxygen depletion and build-up of organic matter. As a result of a thick biomass layer, water flow is reduced and hypoxic conditions prevail; the imbalance between aerobic and anaerobic processes can influence the net ecosystem metabolism and its carbon budget. We here present results from a multi-year investigation (2013-2015) carried out on a mesotrophic shallow lake of south-west of France (Lacanau Lake), where 10% of surface is occupied by dense beds of Egeria densa and Lagarosiphon major. Investigations were carried out through multiple approaches, such as 24h-cycle water collection, GIS mapping, growth rates measurements and sedimentary organic matter assessment. Results from this study revealed that, thanks to advantageous hydrodynamics local conditions (strong wind), those plants do not necessarily trigger water stagnation and hypoxia. Nevertheless, their fast growth generates the accumulation of a huge quantity of labile litter, which feeds respiration processes and methanogenesis on the bottom of the macrophytes bed. Our study underlines that dense aquatic weed mats may constitute important hotspots for greenhouse gases emissions at our latitude, notably enhanced by mild temperature and strong irradiation all over the year.
(pp. 17, 23/04/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Radar altimetry backscattering signatures at Ka, Ku, C, and S bands over West Africa
This study presents a comprehensive comparison of radar altimetry signatures at Ka-, Ku-, C-, and S-bands using SARAL, ENVISAT and Jason-2 data over the major bioclimatic zones, soil and vegetation types encountered in West-Africa, with an emphasis on the new information at Ka-band provided by the recently launched SARAL–Altika mission. Spatio-temporal variations of the radar altimetry responses were related to changes in surface roughness, land cover and soil wetness. Analysis of time series of backscattering coefficients along the West African bioclimatic gradient shows that radar echoes at nadir incidence are well correlated to soil moisture in semi-arid savannah environments. Radar altimeters are able to detect the presence of water even under a dense canopy cover at all frequencies. But only measurements at Ka-band are able to penetrate underneath the canopy of non-inundated tropical evergreen forests.
(Physics and Chemistry of the Earth. Parts A/B/C. vol. 83-84, n° 1474-7065, pp. 96-110, 23/04/2026)
GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, USTTB
Atlas des diatomées des eaux douces de la Réunion
L’ile de la Réunion, de par son caractère insulaire et son isolement, présente de grandes particularités des assemblages biologiques, doublée d’un fort taux d’endémisme. Les diatomées des cours d’eau ne font pas exception à ce constat, et étaient fortement méconnues jusqu’à un passé récent. Or la connaissance des espèces présentes et de leur écologie est le premier pas pour leur protection face aux pollutions et aux pressions qui s’exercent sur leurs habitats. Un programme de recherche-développement financé par l’Office de l’Eau de la Réunion, la DEAL Réunion, le FEDER et l’ONEMA a été lancé à partir de 2008 et a duré jusqu’à fin 2013. Il a été conduit par le consortium Asconit-Cemagref (devenu depuis Irstea). Le but était d’identifier les espèces diatomiques locales, de les nommer, de leur affecter une écologie et une écologie de l’altération, de fonder un nouvel indice diatomique adapté à l’évaluation des cours d’eau de la Réunion (l’IDR) et de transférer cette nouvelle méthode avec la production des documents et outils d’accompagnement (guide méthodologique, guide taxonomique, outil de calcul sous R et sa notice d’utilisation etc. Au cours de ce programme, 343 taxons ont pu être identifiés ou reconnus à l’espèce, certains non trouvés dans la littérature taxonomique mondiale se voyant affecter un code de genre et un numéro d’espèce. Le présent Atlas taxonomique édité par l’Office de l’Eau de la Réunion contient un grand nombre de fiches-taxons décrivant la plupart de ces espèces locales, avec des indications morphologiques et des supports iconographiques au microscope optique et électronique permettant de les reconnaître et de les déterminer : des cartes chorologiques permettant de résumer à quels sites ou dans quels cours d’eau on les trouve, de façon différenciée aux deux saisons ; et enfin, des figurations permettant de situer et de résumer leurs caractéristiques autoécologiques par rapport à des variables abiotiques naturelles et à d’autres sous forte influence des altérations anthropiques.
(pp. 230, 23/04/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse