Seasonal progression of diatom assemblages in surface waters of Ryder Bay, Antarctica
Phytoplankton assemblages from seasonally sea-ice covered Ryder Bay (Adelaide Island, Antarctica) were studied over three austral summers (2004-2007), to link sea-ice variability and environmental conditions with algal speciation. Typical of near-shore Antarctic waters, biomass was dominated by large diatoms, although the prymnesiophyte Phaeocystis antarctica was numerically dominant. Although there was considerable interannual variability between main diatom species, high biomass of certain species or species groups corresponded consistently to certain phases of seasonal progression. We present the first documentation of an extensive bloom of the late-season diatom Proboscia inermis in February 2006, accounting for over 90% of diatom biomass. At this time, water column stratification and nutrient drawdown were high relative to other periods of the study, although carbon export was relatively low. Melt water flux in this region promotes well-stratified surface waters and high chlorophyll levels, but not necessarily concurrent increases in export production relative to seasons with lower freshwater inputs.
(Polar Biology. vol. 33, n° 0722-4060, pp. 13-29, 01/01/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BAS, NERC
What drives the millennial and orbital variations of δ18Oatm?
(Quaternary Science Reviews. vol. 29, n° 0277-3791, pp. 235-246, 01/01/2010)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UNIBE, ITU
Testing the Hypothesis of Fire Use for Ecosystem Management by Neanderthal and Upper Palaeolithic Modern Human Populations
Background: It has been proposed that a greater control and more extensive use of fire was one of the behavioral innovations that emerged in Africa among early Modern Humans, favouring their spread throughout the world and determining their eventual evolutionary success. We would expect, if extensive fire use for ecosystem management were a component of the modern human technical and cognitive package, as suggested for Australia, to find major disturbances in the natural biomass burning variability associated with the colonisation of Europe by Modern Humans. Methodology/Principal Findings: Analyses of microcharcoal preserved in two deep-sea cores located off Iberia and France were used to reconstruct changes in biomass burning between 70 and 10 kyr cal BP. Results indicate that fire regime follows the Dansgaard-Oeschger climatic variability and its impacts on fuel load. No major disturbance in natural fire regime variability is observed at the time of the arrival of Modern Humans in Europe or during the remainder of the Upper Palaeolithic (40-10 kyr cal BP). Conclusions/Significance: Results indicate that either Neanderthals and Modern humans did not influence fire regime or that, if they did, their respective influence was comparable at a regional scale, and not as pronounced as that observed in the biomass burning history of Southeast Asia.
(PLoS ONE. vol. 5, n° 1932-6203, pp. e9157, 24/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PACEA, UB, CNRS, WITS
Experimental toxicity and bioaccumulation of cadmium in freshwater periphytic diatoms in relation with biofilm maturity
A study was undertaken to examine cadmium accumulation in freshwater biofilm, its effects on biofilm development and on diatom community structure in laboratory experimental conditions. A suspension of a biofilm originated from the Riou-Mort River (South West France) was inoculated into three experimental units containing clean glass substrates under laboratory conditions. Settling and already developed biofilms were exposed to a Cd concentration of 100 μgL−1. Metal accumulation (total and intracellular metal content) in biofilms, dry weight and ash-free dry mass, diatom cell density and diatom community composition were analyzed. Both total and intracellular Cd accumulated by the biofilm throughout the experiment increased with duration of metal exposure. Biofilms in the course of maturation were showed higher Cd content and less effective development than settled biofilms. However diatom communities in younger biofilms exposed to Cd increased their tolerance to Cd by a highly significant development of Nitzschia palea. In contrast, Cd exposure had different effect in installed biofilm and taxonomic composition. These results indicate that mature biofilm may limit Cd accumulation into its architecture and protect diatom communities from the effects of metals.
(Science of the Total Environment. vol. 408, n° 0048-9697, pp. 552-562, 24/02/2026)
IRSTEA, UR REBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Viability of differentiated epilithic bacterial communities in the River Garonne (SW France)
Epilithic bacterial community viability was assessed on natural biofilm assemblages from environmentally contrasting locations over a 17-months period to determine if it reflects environmental conditions or conditions within the biofilm assemblage. Vital state was assessed by membrane integrity using LIVE/DEAD® BacLight staining kit. Samples were regularly collected in a large river, up and downstream of a large urban centre. Epilithic biomasses were similar between sites irrespective of the distinct water quality but varied temporarily, peaking up to 48 g AFDM m−2. Bacterial community composition assessed by 16S rDNA based PCR-DGGE significantly differed between sites. Bacterial densities (median of 2.5 × 1011 cell g AFDM−1) were stable whatever the sample origin or biomass. Viable bacterial fractions ranged between 13 and 83% of the total bacterial densities and were correlated with hydrological stability indicators (average of 41.9% during stable water periods, 62.4% during intermediate flow regimes and 50.0% during flow instability) and seasonal parameters. At the river section and epilithic community scales, consistent bacterial densities per unit of biomass could reflect a biofilm assemblage carrying capacity while variable membrane integrity likely integrates changes in the vital state of the community under changing environmental conditions.
(Hydrobiologia. vol. 637, n° 0018-8158, pp. 207-218, 24/02/2026)
CNRS, UR MALY, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Structural vs functional approaches: A first comparison between WFD indicators and Ecological Network Analysis indices on French estuaries
At summary: general context, issue indicators, material and methods data, results.
(pp. 22, 24/02/2026)
UR EPBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
PREDATION OF MUDFLAT MEIO-MACROFAUNAL METAZOANS BY A CALCAREOUS FORAMINIFER, AMMONIA TEPIDA (CUSHMAN, 1926)
Benthic foraminifera are heterotrophic protists that utilize different trophic mechanisms and nutritional resources. They exhibit a wide range of trophic behaviours: selective (grazing) and indiscriminate herbivory, symbiosis, carnivory, parasitism, uptake of dissolved organic matter, passive suspension feeding and, most commonly, deposit feeding. The benthic foraminifera Ammonia tepida, previously known as an herbivore, fed as a carnivore in laboratory experiments where mobile metazoans were provided. We observed predation on the three types of metazoans provided: nematodes, copepods, and a larval gastropod. This foraminifera used its pseudopodial network to entrap the invertebrates, which were then stripped of their soft internal tissues within 24 hours. Our experiments are the first to demonstrate that Ammonia tepida, despite its limited motility, is able to utilize larger mobile animals as a food source. The great abundance of small metazoans in most marine environments suggests that they are a food source for foraminifera. Further study of foraminiferal feeding strategies will enhance our understanding of their role in marine communities.
(Journal of Foraminiferal Research, n° 0096-1191, 24/02/2026)
LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BIAF, UA, UAG, UPMC, UNS, CNRS
Changes in precipitation regimes over North America during the Holocene as recorded by mineralogy and geochemistry of Gulf of Mexico sediments
Changes in terrigenous-transfer patterns from North America toward the Gulf of Mexico via the Mississippi River during the Holocene were investigated using mineralogical and geochemical records from the northern Gulf of Mexico (Pigmy Basin). Clay mineralogy (smectite/illite + chlorite) and geochemical signatures (K and Ti intensities) indicate fluctuations in the detrital sedimentation during the Holocene in the Pigmy Basin. They likely reflect alternations between at least two dominant terrigenous sources: the smectite-rich NW Mississippi watershed, and the illite-and chlorite-rich Great Lakes province and NE Mississippi watershed. These recurring and rapid modifications of erosional processes over this period suggest changes in the hydrological regime via rainfall patterns. Such a modification during the Holocene is likely linked with the rapid atmospheric reorganization following the final collapse of the Laurentide Ice Sheet. Indeed, mineralogical and geochemical proxies indicate east-to-west migrations of the main detrital source (from the Great Lakes and northeastern province toward the northwestern province) associated with Mississippi River megaflood episodes. These modifications of the main detrital sources likely record migrations of the precipitation belt, which are constrained by atmospheric configuration (Jet Stream, Bermuda High and Intertropical Convergence Zone position) and subtropical oceanic hydrological properties (meridional extension of the Atlantic Warm Pool). In the frame of previously published rainfall patterns over the Caribbean and North America, our results highlight some marked modifications of moisture transfer throughout the Holocene. These changes are interpreted as resulting from two atmospheric configurations that have driven alternately the precipitation distribution over North America for the last 10 ka with an apparent cyclicity of~2.5 ka. The coherent common cyclicity between the Gulf of Mexico detrital parameters and Greenland atmospheric proxies over the Holocene suggests that the initial external forcing was rapidly transferred latitudinally through atmospheric processes.
(Global and Planetary Change. vol. 74, n° 0921-8181, pp. 132 - 143, 24/02/2026)
CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], IUEM, IRD, INSU - CNRS, UBO EPE, CNRS, USF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
100,000 Years of African monsoon variability recorded in sediments of the Nile margin
Multiproxy analyses were performed on core MS27PT recovered in hemipelagic sediments deposited on the Nile margin in order to reconstruct Nile River palaeohydrological fluctuations during the last 100,000 years. The strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source, oscillating between a dominant aeolian Saharan contribution during arid periods and a dominant Nile River contribution during pluvial periods. Iron content shows a strong correlation with strontium and neodymium isotopes. This allows the use of a high-resolution continuous Fe record as a proxy of Blue Nile sediment input over the last 100,000 years. The detailed Fe record, with approximately 10 years resolution during pluvial periods, is consistent with subtropical African records of well-dated lake level fluctuations and thus constitutes a first continuous high resolution record of the East African monsoon regime intensity over Ethiopia.;The detailed Fe record shows the two main known pluvial periods attributed to strengthening of the African monsoon over Ethiopia, the Nabtian period from 14 to 8 ka cal BP and the Saharan period from 98 to 72 ka BR For the first time, the last glacial period (Marine Isotope Stage (MIS) 2,3 and 4) is documented with a continuous record showing large oscillations between high and low East African palaeo-monsoon regimes.;The end of the Nabtian period occurred at 8 ka in core MS27PT, i.e. much earlier than on the East Equatorial African region where it ended around 5.5 ka. We interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the Eastern Ethiopian Highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka. During the last glacial period, two wet periods are present around 60-50 ka BP and 38-30 ka BP. These two humid periods are in phase with the rise of atmospheric CH4 concentrations suggesting that wetland tropical African area was one of the sources of the atmospheric CH4 during the MIS 3. During the Last Glacial Maximum and MIS 4, high Saharan aeolian influxes in phase with records of aeolian dust deposited in East Antarctica are documented. This study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low- and high-latitude climate variability at millennial timescales.
(Quaternary Science Reviews. vol. 29, n° 0277-3791, pp. 1342-1362, 24/02/2026)
GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ETH Zürich, UAG, INSU - CNRS, UM, CNRS
Recovery potential of periphytic biofilm exposed to industrial contamination: field and experimental studies
This study was conducted in a context of impacted hydrosystem remediation in France. The Gironde fluvio-estuarine system has been subjected to polymetallic pollution (Cadmium and Zinc) for over a century, coming from an industrial site specialized in zinc ore treatment carrying contaminated wastes into a small tributary, located about 400 km upstream from the estuary. Since 2007 a major remediation phase has been initiated in the industrial site. This study aims to assess first biological modifications due to remediation procedure on periphytic diatoms biofilms, dominant primary producers in freshwaters. Therefore a yearly biomonitoring of the contamination was conducted in situ through 24 days colonizations cycles along the pollution gradient. The experiments were renewed every 48 days during a year. Glass slides were exposed in three stations located upstream the industrial site and one station dowstream the factory (Joany). After 24 days of colonization the glass slides were scraped to collect biofilm. Different tests were then performed: analyses of metal bioaccumulation, taxonomic investigations, numerations of diatom densities and biomass, and Chlorophyll a concentrations, completed by physicochemical measurements in water. Cadmium and zinc bioaccumulation concentrations were discriminating factors for biofilms from Joany, reaching maximum concentrations in dry weights (DW) of 861 ± 387 μg Cd.g-1 and 21 256 ± 5 701 μg Zn.g-1. Joany biofilms presented high densities too and low BDI values in comparison with the three other stations of colonization, located upstream the industrial site probably in relation with the important nutrients concentrations at this station due to urban wastewaters. Moreover, special attention was devoted to abnormal forms in the taxonomic investigations as it is established in the literature that contaminants promote abnormal forms frequencies. Maximum abnormality rate was observed in biofilms from Joany with 12, value significantly higher compared to biofilm from the 3 other stations below 5. Consequently, initial results show yet a persistence of metallic contamination in situ and high bioaccumulation in biofilms located dowstream industrial site. However, remediation is already perceivable in comparison with previous studies in which bioaccumulation (DW) reached 1809 ± 200 μg Cd.g-1 and 23 750 ± 2 469μg Zn.g-1 after 24 days of colonization at Joany in August 2004. Regarding the frequency of abnormal forms, it remains in the same order of magnitude of 10 to 20 at Joany according to this previous study . To understand in a detailed and integrated way whether the periphytic biofilm can initiate total or partial recovery, laboratory decontamination experiments free of environmental variations have thus been developped. The aim was to characterize the kinetics of biofilm recovery under controlled conditions after in situ and artificial expositions to Cd and Zn following the same analysis criteria than used for in situ experiments. Firsts results have shown a rapid decrease of metallic bioaccumulation with a return to control concentrations after 14 days under recovery conditions. This kind of results suggests the resurgence of sensitive species and the decrease of abnormal forms frequencies and put out diatom biofilm as an appropriate model to reveal effective recovery of polluted freshwater ecosystems.
(pp. 2, 24/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR REBX, CEMAGREF