Evènements extrêmes en Afrique de l'ouest durant le dernier glaciaire et l'Holocène
(11/04/2026)
OASU, UB, INSU - CNRS, ULR, CNRS, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, L3AB, UB, INSU - CNRS, CNRS, OASU, UB, INSU - CNRS, ULR, CNRS, INRAE, LAB, UB, INSU - CNRS, CNRS, UB, LGF, UP1, CNRS
Long-term evolution (1988-2008) of Zostera spp. meadows in Arcachon Bay (Bay of Biscay)
The spatial variability of seagrass meadows in Arcachon Bay, was studied between 1988 and 2008 using a combination of mapping techniques based on aerial photographs for intertidal dwarf-grass ( Zostera noltii) beds and acoustic sonar for permanently submerged eelgrass ( Zostera marina) populations. The results show a severe decline over the period for both species, as well as an acceleration of the decline since 2005 for Z. noltii. The total surface regression over the studied period is estimated to be 22.8 km 2 for Z. noltii and 2.7 km 2 for Z. marina, which represent declines of 33 and 74% respectively. Environmental data time series spanning the same period were investigated in order to seek the causes for such a decline. The calculated inter-annual trends for temperature, salinity, nitrate plus nitrite, ammonia, suspended sediment and chlorophyll a did not identify any clear environmental change capable of explaining the observed seagrass regression. For instance, no evident sign of eutrophication was observed over the study period. On the other hand, we suggest that the observed variations of ammonia in the inner part of the lagoon are a symptom of the seagrasses' disappearance and thus, a first sign indicating a change of the Arcachon Bay ecosystem towards more instability and vulnerability. Several hypotheses to explain the observed seagrass decay are proposed.
(Estuarine, Coastal and Shelf Science. vol. 87, n° 0272-7714, pp. 357-366, 11/04/2026)
IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Exploitation of trophic resources by fish under stressful estuarine conditions
Despite the high complexity and variability of estuaries, these ecosystems are very productive and play an important role in fish feeding. This paper constitutes a preliminary investigation to test how fish optimize the use of the available trophic resources, by studying trophic preference variability and feeding strategies of some pelagic and demersal fish in the Gironde estuary (southwest France). Fish and their prey were collected approximately every two months from July 2003 to June 2004 in the upstream area of the saline estuary. Stomach content analyses were realized to describe the variability of fish feeding according to their size and the time of year. Intra- and interspecific food niche overlap was evaluated using Schoener's index and a cross-calculation method was used to highlight the general fish trends in predation strategy. Stomach content results showed interspecific and intraspecific variability in fish feeding, which can be explained by their different or evolutionary ecomorphology. Their diets are composed mainly of zooplankton and hyperbenthic crustaceans with temporal variations in the consumed taxa. Optimization of the available trophic resource use, a key element in estuarine resilience, is thus possible due to the temporal adaptation of this structural trophic web. However, in spite of their temporal adaptation capacity, most fish species exhibited a specialist feeding strategy. This result was not expected, especially in the high turbidity of the Gironde estuary; the loss of one of these species could affect the fish trophic web structure and hence the resilience of the system.
(Marine Ecology Progress Series. vol. 400, n° 0171-8630, pp. p. 207 - p. 219, 11/04/2026)
UR EPBX, CEMAGREF, LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Behavioral responses of Crassostrea gigas exposed to the harmful algae Alexandrium minutum
We describe the valve-activity behavior of oysters, Crassostrea gigas, exposed experimentally to the harmful alga Alexandrium minutum (≈ 3500 cell ml− 1) for 7-day periods under laboratory conditions. Our aim was to assess behavioral responses of oyster species during a mimicked bloom exposure. We determined different characteristic parameters of valve activity, such as daily valve opening duration, daily number of micro-closures, and valve-opening amplitude using a High Frequency-Non Invasive valvometer. In comparison with oysters exposed to non-toxic algae, T-Isochrysis or Heterocapsa triquetra, the valve activity of C. gigas is measurably different when exposed to toxic algae A. minutum. Surprisingly, daily valve-opening duration increased, as well as micro-closure activity, while valve-opening amplitude decreased. The response to A. minutum is fast, within 1 h after algae exposure. Following A. minutum exposure, recovery to control patterns was observed within 4-5 days. The behavioral alterations upon exposure to A. minutum can be thus used as a complementary physiological variable to other well-established physiological and biochemical measurements.
(Aquaculture. vol. 298, n° 0044-8486, pp. 338-345, 11/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS
Holocene Antarctic climate variability from ice and marine sediment cores: Insights on ocean–atmosphere interaction
Holocene climate variability in the southeast Atlantic sector of the Southern Ocean and Antarctic is assessed and quantified through integration of available marine sediment core and Antarctic ice core data. We use summer sea surface temperature (SSST) and sea ice presence (SIP) reconstructions from two marine sediment cores recovered north (50 S) and south (53.2 S) of the present day Antarctic Polar Front (APF), as well as an atmospheric temperature and sea ice proxy from the EPICA ice core from Dronning Maud Land (EDML). We find reasonably good agreement in the timing of climate evolution in the analyzed series. Almost all records show a gradual glacial-to-Holocene climate transition, interrupted by the Antarctic cold reversal around 13 000 cal yr BP, and early Holocene climatic optimum (HCO) at about 11 000 cal yr BP. During the early HCO, the seasonal ice cover retreats to south of 53 S; it then readvances in the course of the mid-to late Holocene. The maximum winter sea ice edge position during the recent 10 000 years varied mainly within 51-53 S, with sporadic growth to north of 50 S, a position similar to that during the last glacial. The onset of the Neoglacial period after ca 4000 yr BP is associated with a steepening of the SSST gradient between the marine core sites, strengthening of the westerlies and cooling in the inland ice sheet. The agreement in timing between elevated SSST during the early HCO and decreased deuterium excess in EDML and other ice cores from different locations in the East Antarctic suggests that the retreat of sea ice during the early HCO and weakening of the APF was a general feature of the East Antarctic climate during that time.
(Quaternary Science Reviews. vol. 29, n° 0277-3791, pp. 303-312, 11/04/2026)
UiT, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impact of solid waste disposal on nutrient dynamics in a sandy catchment
Groundwaters impacted by mature landfill leachate are generally enriched in ammonium. In order to assess the dynamics of ammonium exchanges between leachates and the water system inside a sandy permeable catchment we measured ammonium, nitrate and chloride concentrations in the stream and in sediment pore waters of the streambed of a landfill impacted aquifer. Geophysical investigation methods complemented the biogeochemical survey. The studied zone is a 23 km² catchment located in a coastal lagoon area sensitive to eutrophication risk. Ammonium concentrations in the river were up to 800 µmol l−1 during low water period in summer. Three surveys of the river chemistry showed a regular increase in ammonium, nitrate and chloride concentrations along a 1 km section of the watercourse, downstream the landfill, implying that the leachate plume exfiltrates along this section. Sediment cores collected within this section showed all an increase in ammonium concentrations with depth in pore waters as a consequence of the landfill leachate dispersion, as attested by a simultaneous increase in chloride concentrations. Nitrate enrichment in the river water was due to nitrification of ammonium at the interface between groundwater and streamwater. The apparent nitrification rate obtained was within values reported for turbid estuaries, although the river contained very little suspended particulate matter. Actually, pore water chemistry suggests that nitrification occurred for the most part in subsurface permeable sediments, rather than in stream water. The overall topographic, hydrological, geochemical, and geoelectrical data set permit to estimate the extension of the chloride and ammonium plume. The estimation of the apparent ammonium plume velocity is 23 m year−1 whereas the chloride plume velocity should be 50 m year−1. The river is the outlet of the impacted groundwaters. Considering that the input of ammonium from the landfill is balanced by the present day output via the river, the residence time of ammonium in the aquifer is between 7 and 18 years.
(Journal of Contaminant Hydrology. vol. 116, n° 0169-7722, pp. 1-15, 11/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, Ghymac, UB, EGID
THE EXTENSION OF ID11 FOR NANOSCALE AND HIERARCHICAL CHARACTERIZATION
Beamline ID11 at the ESRF has been recently upgraded by the complete redesign of the optics and by the extension of the beamline to 100 m in length. This has been coupled with the construction of a dedicated endstation for micro- and nano-focusing applications for diffraction and microscopy experiments in solid state chemistry, physics and materials science. Parallel detector schemes allow simultaneous characterization of samples over many length scales and throughout a multi-dimensional parameter space. We report the current ID11 scientific and technical status and the ongoing evolution.
(pp. 457-476, 11/04/2026)
ESRF, CEMHTI, UO, INC-CNRS, CNRS, LCND, LMA, AMU, ECM, CNRS, MATEIS, UCBL, INSA Lyon, INSA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DTU
The European carbon balance. Part 3: forests
(Global Change Biology. vol. 16, n° 1354-1013, pp. 1429-1450, 11/04/2026)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, ICOS-ATC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, MPI-BGC, UNITUS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHYSE, INRA, CNR, UNIBO, EFI, TKK, VU, ICOS-RAMCES, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, MOSAIC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Fish under influence: a macroecological analysis of relations between fish species richness and environmental gradients among European tidal estuaries
Estuarine fish assemblages are subject to a great environmental variability that largely depends on both upstream fluvial and downstream marine influences. From this ecohydrological view, our study introduces a macroecological approach aiming to identify the main environmental factors that structure fish assemblages among European tidal estuaries. The present paper focuses on the influence of large scale environmental gradients on estuarine fish species richness. The environment of 135 North-eastern Atlantic estuaries from Portugal to Scotland was characterized by various descriptors especially related to hydromorphology. Major environmental trends among estuaries were underlined using multivariate techniques and cluster analyses applied to abiotic data. In particular, an integrative system size covariate was derived from a principal component analysis. Factors explaining patterns of species richness at different scales from local habitat to regional features were highlighted. Based on generalised linear models, the estuarine system size, and more particularly the entrance width, and also the continental shelf width were identified as the best explanatory variables of estuarine fish species richness at a large scale. Our approach provides a standardized method to estimate the relationship between fish assemblages and environmental factors. This constitutes a first step in assessing estuarine ecological status and studying the effects of additional factors such as anthropogenic disturbances.
(Estuarine, Coastal and Shelf Science. vol. 86, n° 0272-7714, pp. p. 137 - p. 147, 11/04/2026)
UR EPBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ESE, INRA, ULISBOA
Temporal variability of carbon recycling in coastal sediments influenced by rivers: assessing the impact of flood inputs in the Rhône River prodelta
River deltas are particularly important in the marine carbon cycle as they represent the transition between terrestrial and marine carbon: linked to major burial zones, they are reprocessing zones where large carbon fluxes can be min-eralized. In order to estimate this mineralization, sediment oxygen uptake rates were measured in continental shelf sediments and river prodelta over different seasons near the outlet of the Rhône River in the Mediterranean Sea. On a selected set of 10 stations in the river prodelta and nearby continental shelf, in situ diffusive oxygen uptake (DOU) and laboratory total oxygen uptake (TOU) measurements were performed in early spring and summer 2007 and late spring and winter 2008. In and ex situ DOU did not show any significant differences except for shallowest organic rich stations. Sediment DOU rates show highest values concentrated close to the river mouth (approx. 20 mmol O 2 m −2 d −1) and decrease offshore to values around 4.5 mmol O 2 m −2 d −1 with lowest gradients in a south west direction linked to the preferential transport of the finest riverine material. Core incubation TOU showed the same spatial pattern with an averaged TOU/DOU ratio of 1.2±0.4. Temporal variations of sediment DOU over different sampling periods, spring summer and late fall, were limited and benthic mineralization rates presented a stable spatial pattern. A flood of the Rhône River occurred in June 2008 and delivered up to 30 cm of new soft muddy deposit. Immediately after this flood, sediment DOU rates close to the river mouth dropped from around 15-20 mmol O 2 m −2 d −1 to values close to 10 mmol O 2 m −2 d −1 , in response to the deposi-tion near the river outlet of low reactivity organic matter associated to fine material. Six months later, the oxygen distribution had relaxed back to its initial stage: the initial spatial distribution was found again underlining the active microbial degradation rates involved and the role of further deposits. These results highlight the immediate response of the sediment oxygen system to flood deposit and the rapid relaxation of this system towards its initial state (6 months or less) potentially linked to further deposits of reactive material.
(Biogeosciences. vol. 7, n° 1726-4170, pp. 1187-1205, 11/04/2026)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, OCEANIS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LEP, EEP, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité, CEFREM, UPVD, INSU - CNRS, CNRS, LECOB, SU, CNRS, OOB, SU, CNRS