Sea ice seasonality during the Holocene, Adélie Land, East Antarctica
Thin sections of laminated cores from different Antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale. Here we present the relative abundances of four diatom species and species groups (Fragilariopsis curta group as a proxy for yearly sea ice cover, F. kerguelensis as a proxy for summer sea-surface temperature, Chaetoceros Hyalochaete resting spores as a proxy for spring sea ice melting and the Thalassiosira antarctica group as a proxy for autumn sea ice formation) in core MD03-2601 retrieved off Adélie Land on the Antarctic continental shelf. These abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years. Both the marine records and the simulated climate demonstrated a cooler Early Holocene (9000-7700 years BP), a warmer Mid-Holocene (7700-4000 years BP) and a colder Late Holocene (4000-1000 years BP). Yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the Mid-Holocene Hypsithermal than during the Late Holocene Neoglacial. However, diatom census counts and model output indicate that sea ice spring melting happened earlier in the season, as expected, but that autumn sea ice formation also occurred earlier in the season during the Hypsithermal than during the colder Neoglacial, thereby following seasonal changes in local insolation.
(Marine Micropaleontology. vol. 66, n° 0377-8398, pp. 222-232, 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Long term survey of heavy metal pollution, biofilm contamination and diatom community structure in the Riou-Mort watershed, South West France
In a metal-polluted stream in the Riou Mort watershed in SW France, periphytic biofilm was analyzed for diatom cell densities and taxonomic composition, dry weight and metal bio-accumulation (cadmium and zinc). Periphytic diatom communities were affected by the metal but displayed induced tolerance, seen through structural impact (dominance of small, adnate species) as well as morphological abnormalities particularly in the genera Ulnaria and Fragilaria. Species assemblages were characterized by taxa known to occur in metal-polluted environments, and shifts in the community structure expressed seasonal patterns: high numbers of Eolimna minima, Nitzschia palea and Pinnularia parvulissima were recorded in Summer and Autumn, whereas the species Surirella brebissonii, Achnanthidium minutissimum, Navicula lanceolata and Surirella angusta were dominant in Winter and Spring. Commonly used indices such as the Shannon diversity index and Specific Pollution Sensitivity Index reflected the level of pollution and suggest seasonal periodicity, the lowest diversities being observed in Summer.
(Environmental Pollution. vol. 151, n° 0269-7491, pp. 532-542, 09/04/2026)
UR REBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UT3, Comue de Toulouse
The "storm of the century" (December 1999) and the accidental escape of Siberian sturgeons (Acipenser baerii) into the Gironde estuary (Southwest France): an original approach for metal contamination
Goal, Scope and Background. The Gironde estuary is considered as a reference ecosystem with a large fish assemblage (75 species) and the presence of eleven diadromous species. However, geochemical studies and biomonitoring using oysters have shown high metal pollution levels. During the December 1999 hurricane, more than 5,000 young Siberian sturgeons (Acipenser baerii) accidentally escaped from a fish farm into the estuary, where this species had not been present until then. Methods. In 2002/2003, thirteen sturgeons were collected from the estuary and twelve were obtained from the fish farm, from the same initial batch. Analysis of five metals (cadmium, zinc, copper, lead, mercury) measured in the gills, muscle, liver and kidneys, revealed significantly higher levels of cadmium, lead and mercury in the sturgeon collected from the estuary compared with those from the fish farm. Results and Discussion. Metal analysis of the stomach contents of fish collected from the estuary and artificial food used in the fish farm indicated that dietary exposure might account for the differences observed. Nevertheless, metal concentrations in sturgeons that had spent about three years in the Gironde estuary may be considered low when compared with other species (mullets, eels) or with data in the literature regarding concentrations able to induce structural and functional perturbations in fish. As the introduced Siberian sturgeons live in the same place and feed on the same prey as the juveniles of the endangered A. sturio, our results indicate in the short term that this strictly protected species does not appear to be much affected by the polymetallic pollution in the Gironde estuary. Marked differences in the concentrations of three metals (Cd, Pb, Hg) were established in four organs (gills, liver, skeletal muscle, kidneys) of Siberian sturgeons between specimens that had accidentally escaped into the Gironde estuary (France) during the December 1999 hurricane and were collected in March/June 2003 and specimens from the same initial batch at the fish farm. Recommendations and Perspectives. Based on these results, a programme will be set up, with sampling campaigns carried out in the estuary every two years, with systematic monitoring of age in order to check the origin of individuals, in conjunction with sampling of sturgeon from the fish farm. This programme will complement other studies on several biological species representative of the main trophic levels in the estuary, especially the plankton component, benthic macroinvertebrates and oysters.
(Environmental Science and Pollution Research. vol. 15, n° 0944-1344, pp. 89-94, 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR EPBX, CEMAGREF, UB
Seasonal effects of cadmium accumulation in periphytic diatom communities of freshwater biofilms
The relationships between diatom species and cadmium (Cd) accumulated in biofilms of the Riou-Mort River (SW, France) were studied in July 2004 and March 2005. Biofilms were sampled from artificial substrates immersed along a metallic pollution gradient during 20 days. Dynamics of diatom communities and cadmium accumulation were followed by collecting samples after 4, 7, 14 and 20 days of biofilm colonization. Cd accumulation in biofilms during experiment was significantly higher in Cd polluted station (Joanis) than in reference station (Firmi) for both seasons. Periphytic diatom composition varied between sites and seasons. At Firmi station, seasonal dynamics of diatom communities were stable with the dominance of Cyclotella meneghiniana and Melosira varians in July and Surirellabrebissonnii and Navicula gregaria in March. At Joanis station, diatom communities mainly responded to high levels of metal by a high proportion of small, adnate species. Positive correlations between Eolimna minima, Nitzschia palea, Encyonema minutum, Surirella angusta, and Gomphonema parvulum and cadmium accumulation were observed, indicating that these species are tolerant to high levels of cadmium. On the other hand, negative correlations of C. meneghiniana, N. gregaria, Navicula lanceolata, M. varians and Nitzschia dissipata with cadmium qualify them as sensitive diatom species. Periphytic diatom composition through the presence of specific species highlight metal tolerant indicator diatom groups which will be meaningful for biomonitoring pollution in natural aquatic systems.
(Aquatic Toxicology. vol. 90, n° 0166-445X, pp. 19-28, 09/04/2026)
IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR REBX, CEMAGREF
Les micropolluants sont-ils responsables des déformations observées chez les crevettes blanches de l'estuaire de la Gironde ? Description du phénomène et recherches en cours
Présentation et analyse des déformations observées sur la crevette blanche dans l'estuaire de la Gironde.
(pp. 11, 09/04/2026)
UR EPBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
In-Water Reflectance Spectra Measured On Board a Jet-Ski Across a Complex Nearshore Zone of Case-2 Waters during the ECORS Experiment
(pp. CDrom, 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CRC, UB, CNRS
Cadmium toxicity and bioaccumulation in freshwater biofilms
A microcosm study was undertaken to examine the effects of dissolved cadmium at various concentrations (0, 10, and 100 μg · L−1) on biofilm accumulation and diatom assemblages. A natural biofilm sampled from the Riou-Mort River (Southwest France) was inoculated into three experimental systems, where biofilm settled on glass slides. Samples collected after 1, 2, 4, and 6 weeks of colonization were analyzed for metal accumulation (total metal content and intracellular metal content in the biofilm), biomass (as measured through dry weight and ash-free dry matter), and quantitative as well as qualitative analysis of diatom assemblages. There was a positive correlation between cadmium accumulation and dissolved cadmium concentrations and duration of exposure: a linear relationship was found between concentration factors (CFs) of growing biofilms and time (CFs/day = 0.25 and 0.38 under contaminations of 10 and 100 μgCd · L−1, respectively). Biofilm settlement, more than photosynthetic activity, was affected by high cadmium concentrations: we observed for all stages of settlement a drastic and significant (p < 0.05) reduction in biofilm biomass and in diatom densities in the highest cadmium contamination, compared to control and low cadmium concentration units.
(Archives of Environmental Contamination and Toxicology. vol. 54, n° 0090-4341, pp. 173-186, 09/04/2026)
UR REBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Live and Dead Foraminiferal Faunas from Saint-Tropez Canyon (bay of Fréjus): Observations Based on in Situ and Incubated Cores
The impact of sedimentary processes on the live (rose-Bengal-stained) foraminiferal faunas and on the composition of dead assemblages was investigated at a 373-m-deep station in Saint-Tropez Canyon (Bay of Fréjus, France). For the >150-μm fraction, biocoenoses and thanatocoenoses were investigated in two 10-cm-long cores collected with a classical Barnett multi-corer. In the 63- to 150-μm size fraction, living faunas were investigated in the first centimeter of the sediment. The first core was fixed with ethanol and rose-Bengal at the time of the sampling (the in situ core) whereas the second core was stored in a culture room during a 2.5-year-long incubation before its fauna was investigated.Both cores present similar thanatocoenoses (>150-μm size fraction) that are substantially contaminated by neritic foraminifera presumably transported from adjacent shelves. The sedimentological analysis of a third core reveals neither graded sediments nor erosional surfaces. Abundant organic remains are detected downcore in the muddy silt sediment. All these observations preclude the idea of deposition by a recent turbidite. Therefore, our canyon environment seems to behave at present as a depocenter for a rather continuous flux of fine sediment and resuspended organic matter originating from shallower areas. The living in situ faunas in the 63- to 150-μm and >150-μm size fractions are quite diverse with a moderate evenness. In the >150-μm size fraction, the high abundance of intermediate and deep infaunal taxa (Uvigerina elongatastriata, Bolivina alata, Melonis barleeanus, Globobulimina spp. and Chilostomella oolina) underlines the importance of organic matter focusing (and the related redox conditions) in this submarine canyon environment. The dominance of M. barleeanus and bolivinids in the 63- to 150-μm size fraction confirms the eutrophic aspect of our study area. Because of logistical problems, the incubated core suffered important salinity changes throughout the 2.5 years of incubation. Salinity ranged between 35 and 62 psu. Oxygen concentration was almost zero at the sediment-water interface at the end of incubation. In the larger size fraction (>150 μm), only one taxon, Rosalina bradyi (Cushman, 1915), survived these adverse experimental conditions. Its density (516 ind/100 cm2) is two orders of magnitude higher than that of the in situ core (3 ind/100 cm2). No living foraminifera were found in the first centimeter of the 63- to 150-μm size fraction. Rosalina bradyi was obviously the last species able to reproduce and grow in the incubated core. Our results show that this taxon is capable of tolerating extreme salinity changes.
(Journal of Foraminiferal Research. vol. 38, n° 0096-1191, pp. 137 - 156, 09/04/2026)
LPGN, UN, CNRS, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effects of seasonal dynamics in a Zostera noltiimeadow on phosphorus and iron cycles in a tidalmudflat (Arcachon Bay, France)
A study was conducted in Arcachon Bay, France, to determine the effect of seasonal dynamics in a Zostera noltii meadow on P and Fe cycles in the superficial sediments of a tidal mudflat. The redox-sensitive Fe particulate pool and associated P in the root zone showed a seasonal variation following the growth and decay of Z. noltii biomass, with a maximum content during the growth period. In comparison, the bare sediments did not show significant seasonal changes. A dissolved inorganic phosphorus (DIP) uptake was measured from the water column to the sediment in vegetated sediments, whereas a net DIP efflux was observed in the unvegetated sediments. During the growth period, the formation of an iron oxihydroxide-rich zone occurred and acted as a trap for dissolved phosphorus, constituting a reserve of available P for eelgrass growth. At the periphery of the rhizosphere, a strong reduction of the sediment occurred during the growth phase, probably due to increasing organic matter inputs via the roots. The iron oxihydroxide dissolution releases Fe(II) and the recently bound phosphorus to the pore water, making it available for assimilation by the eelgrass roots for growth metabolism. Fe(II) is re-oxidized to solid Fe(III) forms depleted in P into the root zone, or re-precipitated below as sulphur forms. The highest P uptake occurs by this process, and the seasonal variations in redox-sensitive P stock are sufficient to support the annual Z. noltii P requirement. During the decline period, as the P plant demand and the oxic layer thickness drop, the unused released DIP pool supplies large amounts of DIP to the pore water and water column.
(Marine Ecology Progress Series. vol. 355, n° 0171-8630, pp. 59-71, 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité, LEMAR, IRD, IFREMER, UBO EPE, CNRS
Neanderthal Extinction by Competitive Exclusion
Background: Despite a long history of investigation, considerable debate revolves around whether Neanderthals became extinct because of climate change or competition with anatomically modern humans (AMH). Methodology/Principal Findings: We apply a new methodology integrating archaeological and chronological data with high-resolution paleoclimatic simulations to define eco-cultural niches associated with Neanderthal and AMH adaptive systems during alternating cold and mild phases of Marine Isotope Stage 3. Our results indicate that Neanderthals and AMH exploited similar niches, and may have continued to do so in the absence of contact. Conclusions/Significance: The southerly contraction of Neanderthal range in southwestern Europe during Greenland Interstadial 8 was not due to climate change or a change in adaptation, but rather concurrent AMH geographic expansion appears to have produced competition that led to Neanderthal extinction.
(PLoS ONE. vol. 3, n° 1932-6203, pp. e3972, 09/04/2026)
PACEA, UB, CNRS, KU, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS