Millennial-scale iceberg discharges in the Irminger Basin during the Last Glacial Period: Relationship with the Heinrich events and environmental settings
High-resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the Irminger Basin. The last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from Iceland and corresponding to millennial-scale instabilities of the coastal ice sheets and ice shelves in the Nordic area. A comparison with midlatitude sediment cores shows that ice-rafted material corresponding to the Heinrich events was deposited synchronously from 40 ø to 60øN. There are thus two oscillating systems: every 5-10 kyr massive iceberg armadas are released from large continental ice caps, whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1.2-3.8 kyr. At the time of the Heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems.
(Paleoceanography. vol. 13, n° 0883-8305, pp. 433-446, 01/10/1998)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LDEO, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Infection characteristics of Himasthla elongata cercariae in cockles as a function of water current
Digenean trematodes are widespread parasites of marine fauna. The first intermediate host of Himasthla elongata (Echinostomatidae) is the periwinkle Littorina littorea. The second host is less specific, as it includes various bivalve species. The definitive host is a waterbird. The free-living cercaria acts to ensure transmission from the first and second intermediate hosts. We examined the impact of water flow (still and running water) and host size (6-8, 8-10, 10-12 mm shell length classes) on the settling success of H. elongata cercariae in the second intermediate host by utilizing the common cockle Cerastoderma edule. Under 2 scenarios (free-stream velocity of 0 and 6 cm s-1) more than 90% of the experimental population of cockles (90 individuals per replicate) acquired infections and 60% of the added cercariae were recovered as metacercariae in cockle tissue (mainly foot and siphons). Infection intensity increased significantly with cockle size. Considering the filtering capacity of cockles, the dimension of the flume, and the flow velocity, a passive infection mechanism is proposed based on the suspension feeding activity of the host organism. The scale of potential dispersal of H. elongata is at least a few hundred metres.
(Diseases of Aquatic Organisms. vol. 34, n° 0177-5103, pp. 63 - 70, 11/09/1998)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
Sr, Pb isotopes and REE analyses of five cores of the Red Sea: An insight into hydrothermal input
(30/08/1998)
LHyGeS, ENGEES, UNISTRA, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UAG, INSU - CNRS, UM, CNRS
Improving past sea surface temperature estimates based on planktonic fossil faunas
A new method of past sea surface temperature (SST) reconstruction based on the modem analog technique (Prell, 1985) and on the indirect approach (Bartlein et al., 1986) has been developed: the revised analog method (RAM). Applied to planktonic foraminifera, this technique leads to significant improvements in modern SST reconstruction with respect to former methods: our estimates are characterized by much lower residuals and a better coverage of the observed SST range. Moreover, the error of RAM estimates of past SSTs is lower than that associated with former reconstructions, particularly at middle and high latitudes. In low latitudes, cold season SSTs reconstructed by RAM during glacials are 1 degrees-3 degrees C lower than previously estimated. Our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics.
(Paleoceanography. vol. 13, n° 0883-8305, pp. 272-283, 01/06/1998)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, IMEP, AU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Growth of green sulphur bacteria in experimental benthic oxygen, sulphide, pH and light gradients
(Microbiology. vol. 144, n° 1350-0872, pp. 1051-1061, 01/04/1998)
ECOLAG, UM2, IFREMER, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Crepidula fornicata L. (Mollusca, Gastropoda) in the Marennes-Oléron Bay: side-scan sonar mapping of subtidal beds and stock assessment
Extensive and detailed subtidal ground mapping of the Marennes-Oléron Bay and Fouras-Aix areas was performed with a side-scan sonar. Side-scan sonographs gave a comprehensive view of sedimentological bottom environments and also allowed us to outline locations of grounds colonised by the gastropod mollusc Crepidula fornicata L. with a precise estimate of their surface. A sedimentological map of the centre of the Marennes-Oléron Bay is given, describing spatial organisation of the following four types of sediment: pure mud, fine sand, coarse sand and rocks. Crepidula beds were also recognised on sonographs and were estimated to coyer 181 hectares in the Fouras-Aix area and 615 hectares within the Marennes-Oléron Bay. Standard sampling methods were then combined with the side-scan sonar mapping results, allowing an estimate to be made of the stocks of Crepidula fornicata (live specimens and dead shells). A stratified sampling procedure was performed in April-May 1995, including 80 stations sampled with a Smith McIntyre grab (two grabs per station). The live stock of Crepidula was estimated to be 2 494 ± 3344 tons at Fouras-Aix and 2644 ± 1 137 tons within the bay of Marennes-Oléron. This latter estimate is similar to the previous one performed in this bay in spring 1984, i.e. 1 800 ± 900 tons, due to the overlap of 95 % confidence intervals. These comparable estimates within the Marennes-Oléron Bay give no evidence to suggest that dredging operations (1 000-1 500 tons·yr-1) performed in the bay for 15 years are not efficient. However, annuallanding operations of slipper limpet cannot prevent further spread of the species, as pointed out by the large development of a new Crepidula ground in the north-western centre of the bay (north Lamouroux sand bank). Both natural processes (cuITent action and bed load transport) and bottom-trawl activities can facilitate spread of the species in the bay, as revealed by side-scan sonar image analysis.
(Oceanologica Acta. vol. 21, n° 0399-1784, pp. 353 - 362, 01/03/1998)
LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER
A high-resolution record of the Last Deglaciation in the Central Mediterranean sea: Palaeovegetation and palaeohydrological evolution
(Quaternary Science Reviews. vol. 17, n° 0277-3791, pp. 303-317, 01/01/1998)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOPS, INSU - CNRS, CNRS
Application of modern analog technique to marine Antarctic diatoms: Reconstruction of maximum sea-ice extent at the Last Glacial Maximum
Modern analog technique (MAT) applied to Antarctic diatoms is a new approach for quantitative sea‐ice paleoreconstructions in the Southern Ocean. In a first step we show that MAT is a better approach than the Imbrie and Kipp Method to reconstruct the modern sea‐ice pattern. We then use this approach to reconstruct sea‐ice presence in number of months per year during the last glacial maximum (LGM). At this time, sea‐ice presence was greater than today, leading to a shorter diatom growing season. The maximum sea‐ice extent, inferred from quantitative values of sea‐ice presence, was located 5–8° north of its actual position, leading to double the surface of modern winter sea ice. This greater sea‐ice extent may have played a significant role on atmospheric and surface oceanic circulations and therefore on southern mid‐latitude and high‐latitude climates. It may also have reduced the amount of heat, moisture, and CO2 from the ocean to the atmosphere, thus participating in the lowering of atmospheric CO2 during the LGM
(Paleoceanography. vol. 13, n° 0883-8305, pp. 284-297, 21/02/1998)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LDEO
Acceleration of Horizontal Mean Currents in DNS of Stratified Turbulent Shear Flows
(. vol. 46, pp. 423-424, 21/02/1998)
IMFT, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, CERFACS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Reappraisal of Antarctic seasonal sea ice at the Last Glacial Maximum
We used modern analog technique applied to Antarctic diatoms to quantitatively reconstruct seasonal sea‐ice extent at the Last Glacial Maximum. Winter maximum sea‐ice limit occurred around 48°S in the Atlantic and western Indian sectors, around 55°S in the eastern Indian and western Pacific sectors, and around 58–60°S in the eastern Pacific sector of the Southern Ocean. Summer maximum sea‐ice extents during the last ice age and today are similar, which contradicts CLIMAP's findings. This implies a reduced summer albedo feedback of the Southern Hemisphere and a greater transfer of heat and moisture from the ocean to the atmosphere than shown by previous qualitative studies.
(Geophysical Research Letters. vol. 25, n° 0094-8276, pp. 2703-2706, 21/02/1998)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LDEO