Invasion of the eastern Bay of Biscay by the nassariid gastropod Cyclope neritea: origin and effects on resident fauna
The distribution area of the nassariid gastropod Cyclope neritea (L.) includes the Mediterranean and the Black Sea, as well as the Atlantic coasts of the southern Iberian Peninsula. The species has spread north to the eastern Bay of Biscay (Arcachon Bay in 1976, Marennes-Oléron area and Morbihan Gulf in 1983-84). This spread might be explained either by (1) a natural spread favoured by environmental changes (e.g. an increase of temperature) or (2) a sudden range expansion due to the introduction of individuals from distant native populations. Molecular genetic analyses based on mitochondrial markers suggest that the present C. neritea population in Arcachon Bay has been introduced, probably unintentionally with oyster transfers, from several source populations, genetically similar to the populations analysed in this study, i.e. those in the western Mediterranean and in south Portugal. Within its new distribution area, C. neritea could potentially compete with the autochthonous nassariid Nassarius reticulatus, both species being scavengers. Although C. neritea tends to occur mainly in relatively clean sands in the intertidal and N. reticulatus in subtidal, organic rich sediments, the habitats of both species partially overlap. Laboratory experiments showed that in still water conditions C. neritea was more active and reached carrion faster than N. reticulatus, thereby having a competitive advantage over the latter; flow conditions ( ~1 cm s-1) appeared to stimulate the activity of N. reticulatus. Analysis of parasite load in both species in Arcachon Bay indicated that N. reticulatus was more heavily parasitized by digenean trematodes than C. neritea. This suggests that the spread and population dynamics of C. neritea along the French Atlantic coast has been favoured by the lack of parasites. Altogether, recurrent introduction, competitive ability and lack of heavy parasitic load might explain the successful settlement of C. neritea along the French Atlantic coast.
(Marine Ecology Progress Series. vol. 276, n° 0171-8630, pp. 147 - 159, 02/08/2004)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS, LBEM, ULR, CREMA, IFREMER, CNRS, SBR, UPMC, CNRS
Climatic "pause" during Termination II identified in shallow and intermediate waters off the Iberian margin
The sequence of Termination II, from the end of marine isotopic stage 6 (MIS 6) to MIS 5e, is observed through an isotopic study (δ18O) of planktic and benthic foraminifera in core MD99-2331 (42°09′N; 09°41′W), collected in the North Atlantic, on the Iberian margin. First, to build an approximate time scale, a record of the planktic δ18O signal is achieved from the top of the core (Holocene) to MIS 6. The remarkable similarity of this planktic record to the Greenland Ice Core Project ice core δ18O record allows a rough dating of our core. A focus on Termination II reveals one "standstill" in the benthic record. This "pause" can be linked either to a perturbation of North Atlantic oceanic circulation pattern, as a slowing down of the North Atlantic Deep Water formation, or to an interruption in polar ice sheet melting, which could be a more global phenomenon. © 2004 Elsevier Ltd. All rights reserved.
(Quaternary Science Reviews. vol. 23, n° 0277-3791, pp. 1523-1528, 01/07/2004)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, IRSN/PSE-ENV/SRTE/LRC, IRSN/PSE-ENV/SRTE, IRSN
Etude sédimentologique de la Grande Vasière.
(10/06/2004)
M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GM, IFREMER
The distribution of heavy metals in the Sidi Moussa lagoon sediments (Atlantic Moroccan Coast)
The superficial and cored sediments of the Sidi Moussa lagoon (Atlantic Moroccan coast) have been analysed in order to determine their main characteristics and their heavy metals contents. Two groups of metals can be distinguished: Al, Fe and Cu whose distribution is mainly governed by the intra-lagoonal dynamics. These contents are near of those of the natural geochemical background noise that underlines their natural origin. Zn, Cr and Ni have relatively more elevated contents than the natural geochemical background noise indicating human-made pollution. The geo-accumulation indicator shows that the Sidi Moussa lagoon is moderately polluted. The totality of results in this context compared to the standard values suggested by the Agency of Protection of the Environment of United States leads to the conclusion that the sediments of Sidi Moussa lagoon would rank as slightly polluted for, Cu, Zn, Cr and Ni.
(Journal of African Earth Sciences, n° 1464-343X, pp. 473-483, 01/06/2004)
LETG - Nantes, UNICAEN, NU, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Comparing the Epica and Vostok dust records during the last 220,000 years: stratigraphical correlation and provenance in glacial periods
(Earth-Science Reviews. vol. 66, n° 0012-8252, pp. 63 - 87, 01/06/2004)
CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, LGGE, OSUG, UJF, Grenoble INP, INSU - CNRS, IRSTEA, USMB [Université de Savoie] [Université de Chambéry], CNRS, INSU - CNRS, CNRS, GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A massive dissolved inorganic carbon release at spring tide in a highly turbid estuary
[1] In September 2003, the highly turbid Loire estuary (France) showed drastic oxygen depletions (down to 11% of saturation), high pCO 2 (up to 3740 matm) and high CO 2 fluxes (280 ± 100 mmol.m À2 .d À1). A rapid rise in Dissolved Inorganic Carbon (DIC) was observed when the tidal amplitude increased from 3.8 m to 5.8 m. In two days, average concentrations in the 0.1-25 salinity range increased by 106 ± 17 mmol.kg À1 for DIC, by 80 ± 14 meq.kg À1 for Total Alkalinity (TA) and by 684 ± 142 matm for pCO 2. In parallel, oxygen decreased by 65 ± 12 mmol.kg À1. These changes in concentrations were attributed in majority to a massive fluid mud resuspension in the estuarine turbidity maximum. At spring tide, this DIC input was 30% higher than the river input. When averaged over the neap-spring period, resuspension contributed to only 10% of the atmospheric CO 2 flux from the estuary, but to 60% to the net TA production in the estuary.
(Geophysical Research Letters. vol. 31, n° 0094-8276, pp. n/a-n/a, 16/05/2004)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSN/PSE-ENV/SRTE/LRC, IRSN/PSE-ENV/SRTE, IRSN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Intense summer Si-recycling in the surface Southern Ocean
(Geophysical Research Letters. vol. 31, n° 0094-8276, pp. L09305, 01/05/2004)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, LBCM, UPMC, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Copper detection in the Asiatic clam Corbicula fluminea: optimum valve closure response
When exposed to a contaminant, bivalves close their shell as a protective strategy. The aim of the present study was to estimate the maximum expected dissolved copper sensitivity in the freshwater bivalve Corbicula fluminea using a new approach to determine their potential and limit to detect contaminants. To take into account the rate of spontaneous closures, we integrated stress problems associated with fixation by a valve in usual valvometers and the spontaneous rhythm associated with nycthemeral activity, to optimize the response in conditions where the probability of spontaneous closing was lowest. Moreover, we used an original system with impedance valvometry, using lightweight impedance electrodes, to study free-ranging animals in low stress conditions combined with an analytical approach describing dose-response curves by logistic regression, with valve closure reaction as a function of response time and concentration of contaminant. In C. fluminea, we estimated that copper concentrations >4 μg/l (95% confidence interval (CI95%), 2.3–8.8 μg/l) must be detected within 5 h after Cu addition. Lower values could not be distinguished from background noise. The threshold values were 2.5 times lower than the values reported in the literature.
(Aquatic Toxicology. vol. 66, n° 0166-445X, pp. 333-342, 25/02/2004)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSN/DPRE/SERLAB/LRE, IRSN/DPRE/SERLAB, IRSN, LMBA, UBS, UBO EPE, CNRS
Sédimentation organique profonde sur la marge continentale namibienne (Lüderitz, Atlantique Sud-Est) : impacts des variations climatiques sur la paléoproductivité
L'objectif de cette étude multimarqueurs est de fournir une meilleure compréhension du rôle joué par le système d'upwellings du Benguela vis à vis de la séquestration du carbone au cours des deux derniers cycles climatiques. Les sédiments de la pente continentale namibienne sont riches en matière organique (MO) bien que les processus sédimentaires soient exclusivement hémipélagiques. La première partie de ce travail consiste en la détermination des mécanismes de préservation qui ont participé à la fossilisation de la MO dans la colonne d'eau et le sédiment et leur distribution du haut en bas de pente, au large de Lüderitz (25°6S). Les analyses moléculaires, spectroscopiques, pétrographiques et les pyrolyses révèlent que l'enfouissement de carbone organique était plus efficace pendant les périodes glaciaires du fait de flux de MO accrus vers le sédiment. Ces flux agissent positivement sur l'initiation de mécanismes de fossilisation tels que la sulfuration naturelle. Par ailleurs, des associations organo-minérales dans la colonne d'eau ont probablement été responsables de la protection pendant le transport d'une quantité non négligeable de MO, et assuré son accumulation sur la pente inférieure. Les teneurs en carbone organique varient au rythme des cycles glaciaires-interglaciaires. La deuxième étape de l'étude est donc consacrée à l'estimation des effets des variations climatiques sur la paleoproductivité et les flux exportés. L'étude des signaux d15N, de la taille des particules lithogéniques et des contenus terrigènes et biogènes des sédiments montre que la productivité, soutenue par l'apport de nitrate en surface, n'est que partiellement controllée par la force des alizés. Les advections de masses d'eaux Angolaises, Indiennes et l'utilisation des nutriments en Antarctique conditionnent l'alimentation en nitrate et silicium, le rendement et la nature de la production primaire de l'upwelling à l'échelle des cycles climatiques.
(19/02/2004)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ISTO, INSU - CNRS, UO, CNRS
Late Quaternary sea ice history in the Indian sector of the Southern Ocean as recorded by diatom assemblages
A Modern Analog Technique (MAT 5 201/31) has been applied to fossil diatom assemblages to provide down-core estimates of February sea-surface temperatures (SSTs) and of sea ice duration over the past 220 000 years at 56 ‡40PS, 160 ‡14PE. At the core location, sea ice progression lagged the SST drop by V1 ka at interglacial^glacial transitions, and sea ice retreat was almost synchronous to the SST increase at glacial^interglacial terminations. Sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times, although SSTs were almost constant during glacials. This indicates that SSTs are the major parameter determining the advance and retreat of sea ice at transitions, but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo, air temperature and meridional wind stress. The strong correlation (r = 0.75) between sea ice duration at the core location and the Vostok CO 2 record argues for a control of Antarctic sea ice extent on atmospheric CO 2 concentration via the modification of the ocean-to-atmosphere gas balance. ß
(Marine Micropaleontology. vol. 50, n° 0377-8398, pp. 209-223, 01/02/2004)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS