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, 31/08/2026)
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
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, 31/08/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, INRA
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, 31/08/2026)
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
Trophic opportunism of central Amazon floodplain fish
1. The food web of the central Amazon basin displays one of the largest discrepancies in food source utilisation versus availability for consumers. While C 4 macrophytes dominate the primary producing biomass in floodplains, the food web is dominated by the use of C 3 carbon sources. Amazon fish species have wide-ranging diets and show feeding flexibility in response to spatial and temporal patterns in food source availability. Fish are therefore expected to use a range of available resources. Fatty acids and stable carbon and nitrogen isotopic compositions were studied to investigate their trophic behaviour and provide a better assessment of food source utilisation by nine fish species from two Amazon floodplains. 2. Although nitrogen stable isotopes positioned detritivores at the base of the food chain, their large proportions of polyunsaturated fatty acids (FAs) suggest selection of a high-quality food source, such as microalgae. Omnivores and insectivores displayed a wide range of food source utilisation, indicating opportunist feeding behaviour. Piscivores displayed the most 15 N-enriched signature (up to 10.6&), concomitant with their predator position in the studied food web. 3. C 3 carbon was the dominant source for most species, which is a finding consistent with current classical knowledge. However, consumption of C 4 macrophytes was detected for the herbivore Schiz-odon fasciatus, in line with the spatial availability of this food source in the floodplain system. Large amounts of polyunsaturated and essential FAs in these C 4 macrophytes indicate their high nutritive value. Our results suggest that this food source is rather neglected by fish due to low digestibility, with the exception of the herbivore that may possess modification of its digestive system that allows the use of C 4 plants.
(Freshwater Biology. vol. 60, n° 0046-5070, pp. 1659-1670, 31/08/2026)
UMR ISEM, Cirad, IRD, EPHE, PSL, UM, CNRS, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Stratification of surface waters during the last glacial millennial climatic events: a key factor in subsurface and deep-water mass dynamics
The last glacial period was punctuated by abrupt climatic events with extrema known as Heinrich and Dansgaard–Oeschger events. These millennial events have been the subject of many paleoreconstructions and model experiments in the past decades, but yet the hydrological processes involved remain elusive. In the present work, high-resolution analyses were conducted on the 12–42 ka BP section of core MD99-2281 retrieved southwest of the Faeroe Islands, and combined with analyses conducted in two previous studies (Zumaque et al., 2012; Caulle et al., 2013). Such a multiproxy approach, coupling micropaleontological, geochemical and sedimentological analyses, allows us to track surface, subsurface, and deep hydrological processes occurring during these rapid climatic changes. Records indicate that the coldest episodes of the studied period (Greenland stadials and Heinrich stadials) were characterized by a strong stratification of surface waters. This surface stratification seems to have played a key role in the dynamics of subsurface and deep-water masses. Indeed, periods of high surface stratification are marked by a coupling of subsurface and deep circulations which sharply weaken at the beginning of stadials, while surface conditions progressively deteriorate throughout these cold episodes; conversely, periods of decreasing surface stratification (Greenland interstadials) are characterized by a coupling of surface and deep hydrological processes, with progressively milder surface conditions and gradual intensification of the deep circulation, while the vigor of the subsurface northward Atlantic flow remains constantly high. Our results also reveal different and atypical hydrological signatures during Heinrich stadials (HSs): while HS1 and HS4 exhibit a "usual" scheme with reduced overturning circulation, a relatively active North Atlantic circulation seems to have prevailed during HS2, and HS3 seems to have experienced a re-intensification of this circulation during the middle of the event. Our findings thus bring valuable information to better understand hydrological processes occurring in a key area during the abrupt climatic shifts of the last glacial period.
(Climate of the Past. vol. 11, n° 1814-9324, pp. 1507-1525, 31/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UQAM, IFREMER, LDO, INSU - CNRS, UBO EPE, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
La restauration écologique comme nouveau paradigme d'aménagement ?
Bien que les politiques aménagistes aient permis d'améliorer la maîtrise globale des fleuves, elles ont également généré de nombreuses perturbations et altérations. Aujourd'hui, la restauration des cours d'eau fait l'objet de nouvelles expérimentations. Dans le sud-ouest de la France, sur le fleuve Garonne et l'estuaire de la Gironde, elles se traduisent notamment par des remises en eau des marais liées au passage de tempêtes (dynamique de dépoldérisation). Plus en amont, dans la moyenne Garonne toulousaine, les réflexions en cours concernent la réouverture de bras morts ou la création de zones d'expansion de crues. Nous proposons, de questionner l'émergence de ce nouveau paradigme, dans une perspective pluridisciplinaire, par une évaluation géohistorique, géochimique, écologique et sociologique.
(Cahiers de géographie du Québec. vol. 59, n° 0007-9766, pp. 293-314, 31/08/2026)
GEODE, UT2J, Comue de Toulouse, CNRS, UR ETBX, IRSTEA, UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS
Climbing experience in glass eels: a cognitive task or a matter of physical capacities?
The European eel is a panmictic species, whose decline has been recorded since the last 30 years. Among human induced environmental factors of decline, the impact of water dams during species migration is questioned. Indeed, water impoundments can be a severe obstacle for young eels trying to reach the upstream freshwater zones, even if they are equipped with fish-friendly passes. The passage by such devices could be an important event shaping the outcome of the future life and life history traits of eels. We studied what phenotypic traits were associated with the event of experience of passage by water obstacles. We analyzed specific enzyme activities and/or gene transcription levels in the muscle and brain to test whether the obstacle passage is rather a physical or cognitive task.Wefound that after a long period of maintenance under homogenous conditions, transcription levels of several genes linked to synaptic plasticity, neurogenesis and thyroid activity differed among the field-experience groups. In contrast, muscle gene transcription levels or enzymatic activities did not show any differences among fish groups.We suggest that cognitive processes such as learning and memory acquisition rather than swimming-related metabolic capacities are involved in passage of water obstacles by young eels.
(Physiology & behavior. vol. 151, n° 0031-9384, pp. 448-455, 31/08/2026)
UR EABX, IRSTEA, SEEM, UT3, Comue de Toulouse, CNRS, EDB, IRD, UT3, Comue de Toulouse, CNRS, EDF [E.D.F.], EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Spatial heterogeneity of benthic biogeochemistry in two contrasted marine environments (Arcachon Bay and Bay of Biscay, SW France)
We have studied the heterogeneity of vertical profiles of biogeochemical components obtained from sediment core slicing. Sediment cores were collected in the intertidal zone of the Arcachon Bay and on the continental slope of the Bay of Biscay, at 550 and 1000 m depth. At each station of the Arcachon Bay, five 1 m-side zones were delimited at low tide. In each square, 3 cores were collected. Spatial heterogeneity on the continental slope was obtained from the study of 3 cores of multi-corer while 2 or 3 multi-corer deployments were used during the same oceanographic cruise. Similarity between profiles was determined to estimate the spatial heterogeneity at different scales. In the Arcachon Bay, results showed a spatial heterogeneity at a decimetre scale on apparently homogeneous areas. Despite the spatial variability, all the replicated profiles in Arcachon Bay sediments had similar trends, suggesting homogeneous benthic properties. However, a sampling with replicate cores handling is required for seasonal monitoring or study of biogeochemical mechanisms in coastal environments. We observe that the spatial variability on the continental margin of the Bay of Biscay is lower than in coastal environment of the Arcachon Bay. Heterogeneity is equivalent at a decimetre scale and at a hundred meters scale, which is the precision of the sampling positioning due to the drift of the boat and the tilt of the corer cable. In addition, our 10-year-long database for the Bay of Biscay showed that differences in the shape of profiles obtained in sediment cores collected at the same stations throughout this long period may not be interpreted in terms of evolution with time, because the observed variability is as high as the spatial heterogeneity.
(Estuarine, Coastal and Shelf Science, n° 0272-7714, pp. 51–65, 31/08/2026)
BIAF, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Programme PIREN-Seine - Phase 6 Axe 4 : « Ecologie & Ecotoxicologie » Les déterminants de la qualité écologique du milieu aquatique
Les organismes vivants dans le milieu aquatique sont soumis à de multiples pressions combinées : chimique, hydro- morphologique, thermique, trophique (matière organique, eutrophisation...), qui impactent, et éventuellement perturbent leur fonctionnement. La santé des individus qui composent la biocénose peut aussi être altérée par ces différentes pressions. S'il est possible de faire des relations causales entre une pression et une réponse biologique, l'enjeu aujourd'hui est de pouvoir prédire les conséquences sur les différentes composantes de la biocénose de l'ensemble des pressions qui interagissent. L'observation des organismes vivants, à différents niveaux d'organisation (la cellule, l'organe, l'organisme, la population, ou la communauté) est proposée depuis plusieurs années pour renseigner sur l'état de santé des organismes, des communautés (bio- indication de type DCE), sur l'état écologique global du milieu, ou sur l'impact des contaminants chimiques (biomarqueurs en écotoxicologie). Au cours de la phase 6 PIREN -Seine, nous avons étudié à la fois comment les observations faites sur la biocénose peuvent nous renseigner sur les impacts des différentes pressions, y compris la pression chimique (domaine de l'écotoxicologie), mais aussi comment la multiplicité de ces pressions (caractéristique d'un bassin versant très anthropisé comme l'est celui de la Seine), ou les modifications de ces pressions, impactent le vivant.
(pp. 172, 31/08/2026)
SEBIO, INERIS, URCA, ULH, NU, URCA, CNRS, UR HBAN, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULB, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LSPE - UP-S, UR MALY, IRSTEA
Rapid longitudinal migrations of the filament front off Namibia (SE Atlantic) during the past 70 kyr
Although productivity variations in coastal upwelling areas are mostly attributed to changes in wind strength, productivity dynamics in the Benguela Upwelling System (BUS) is less straightforward due to its complex atmospheric and hydrographic settings. In view of these settings, past productivity variations in the BUS can be better investigated with downcore sediments representing different productivity regimes. In this study, two sediment cores retrieved at ca. 25°-26°S in the BUS and representing different productivity regimes were studied. By using micropaleontological, geochemical and temperature proxies measured on core MD96-2098, recovered at 2910 m water depth in the bathypelagic zone at 26°S off Namibia, variations of filament front location, productivity and temperature in the central BUS over the past 70 kyr were reconstructed. The comparison with newly-generated alkenone-based sea-surface temperature (SST) and previously obtained data at site GeoB3606-1 (~ 25°S; ca. 50 km shoreward from MD96-2098) allowed the recognition of four main phases: (1) upwelling front above the mid slope (70 kyr-44 kyr), (2) seaward displacement of the upwelling front beyond the mid slope (44 kyr-31 kyr), (3) main upwelling front over the hemipelagial (31 kyr-19 kyr), and (4) shoreward contraction of the upwelling filament, and decreased upwelling strength over most of the uppermost bathypelagic (19 kyr-6 kyr). The latitudinal migration of the Southern Hemisphere westerlies and the consequent contractions and expansions of the subpolar gyre played a significant role in millennial and submillennial variability of SST off Namibia. The strength of the southeasterly trade winds, rapid sea-level variations and the equatorward leakage of Antarctic silicate might have acted as amplifiers. Although late Quaternary variations of productivity and upwelling intensity in eastern boundary current systems are thought to be primarily linked to the variability in wind stress, this multi-parameter reconstruction shows that interplaying mechanisms defined the temporal variation pattern of the filament front migrations and the diatom production off Namibia during the past 70 kyr.
(Global and Planetary Change. vol. 125, n° 0921-8181, pp. 1-12, 31/08/2026)
IACT, CSIC, UGR, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, NIOZ, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS