Coccolith evidence for instabilities in surface circulation south of Iceland during Holocene times
(Earth and Planetary Science Letters. vol. 179, n° 0012-821X, pp. 257-268, 01/06/2000)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LDEO
Un paléolac du dernier interglaciaire pléistocène dans l'Extrême-Sud hyperaride de la Jordanie
(Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science. vol. 330, n° 1778-4107, pp. 259-264, 01/02/2000)
JU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ESEP, UJF, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LGQ, CNRS
Phylogenetic relationships of Pleurotus species according to the sequence and secondary structure of the mitochondrial small-subunit rRNA V4, V6 and V9 domains
A comparative study of the V4, V6 and V9 domains of the mitochondrial small-subunit (SSU) rRNA was conducted to evaluate the use of these sequences to investigate phylogenetic relatedness within the genus Pleurotus. The PCR products encompassing these regions from 48 isolates belonging to 16 Pleurotus species were sequenced and compared. From this comparison, the length and sequence of the three domains were found to be constant within a species. Significant inter-species variations due to insertion/deletion events were found, in most cases occurring in regions not directly involved in the maintainance of the standard SSU rRNA secondary structure. Phylogenetic analysis based upon these mitochondrial sequences was in agreement with relationships previously established by morphological descriptions and with previous studies based upon the nuclear genome or isozymes; moreover such analysis resolved some ambiguities in earlier analyses. It was confirmed that P. ostreatus and P. florida represent a single species, as well as P. pulmonarius and P. sajor-caju. The phylogenetic analysis also made it possible to assess the relative positions of P. rattenburyi, P. lampas, P. sapidus, P. colombinus and P. eryngii. The results clearly showed that sequences of the V4, V6 and V9 domains of the mitochondrial SSU rRNA could provide good markers for use in the taxonomy and phylogeny of species of Basidiomycota. Because of their nucleotide conservation, the major advantage of these species-specific markers was the possibility to study only one isolate from each species to determine phylogenetic relatedness.
(Microbiology. vol. 146, n° 1350-0872, pp. 209-221, 01/01/2000)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Premières observations sur la morphologie et les processus sédimentaires récents de l’Éventail celtique
First observations on the morphology and recent sedimentary processes of the Celtic Deep Sea Fan. During the SEDIFAN 1 cruise we surveyed the bathymetry and the acoustic properties of the surface sediment of the Celtic Deep Sea Fan. We also collected Küllenberg cores in order to study recent sedimentary processes. From the bathymetry survey it is relatively easy to recognize the main areas of modern fan. The upper fan included a large sedimentary ridge which constitutes the right levee of the prominent meandering Whittard valley. After its confluence with the Shamrock valley the course of the Whittard valley is abruptly deflected to the south. At a short distance to the south the valley divides into two upper-fan channels, the Celtic channel to the west being the deeper one. This point constitutes the centre of a radiating pattern which is developed on a 150° quadrant and a radius of about 100 km. The acoustic imagery displays contrasted features, related to change in lithology within the first metre beneath the sea bottom and to the sea floor roughness. The Austell ridge exhibits a contrasted pattern of elongated areas with high and low acoustic backscattering levels. This pattern is related to the development of abyssal dunes, the amplitude of which is of metric order. Particularly remarkable is a lobe-shaped low back-scattering area in the western part of the middle fan, also noteworthy are a lineated facies to the west and a braided facies to the east of the fan. The laminated silty-clayey sequences deposited on the Whittard ridge and on the Trevelyan levee were deposited during the deglaciation. We interpret these as turbidity currents overflow deposits from the Whittard valley. At the end of isotopic stage 3 and during stage 2, the English Channel was a large plain flooded by the Channel River. During this period a broad delta developed at 100 m below the present-day depth and a wide spectrum of material was bound to be supplied to the deep sea and contributed particularly to the deposition of the Whittard ridge silty-clayey sequences. The stage 2 deposits are characterized by rhythmic levels enriched in monosulfides. These types of deposits are common in areas affected by fluvial discharges. Excluding the sedimentary ridge and the channel levees the surface deposits sampled with the Küllenberg corer are sandy. These sands are deposited in various contexts on the interfluve between the western and eastern channels and at channel mouths. They were emplaced during high sea level stands as a result of high energy gravity processes. The precise sources of these sands have not yet been identified, however benthic foraminifers from included ooze pebbles have living depths of between 500 and 1 000 m. The gravity processes which eroded this marly ooze may have been triggered on the upper slope. The Celtic shelf is presently a high energy platform where the conjunction of storms and spring tides can lead to enhanced sediment transport from near-shore to the deep sea. The relict or palimpsest deposits of the glacial delta also constitute a large reservoir of sandy material which can also be subject to reworking. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SASdeep-sea fan / Quaternary / sediment / turbidity / palaeoclimate
(Oceanologica Acta. vol. 23, n° 0399-1784, pp. 109-116, 01/01/2000)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Were the North Atlantic Heinrich events triggered by the behavior of the European ice sheets?
(Geology. vol. 28, n° 0091-7613, pp. 123, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, IFREMER
Hydrological Impact of Heinrich Events in the Subtropical Northeast Atlantic
Reconstructing the impact of Heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events. A high-resolution study of a marine sediment core from the Iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low-salinity arctic water masses during the last three Heinrich events. These paleoclimatic time series reveal the internal complexity of each of the last three Heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments.
(Science. vol. 289, n° 0036-8075, pp. 1321-1324, 21/02/2026)
CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Spatial variations in nutrient utilization, production and diagenesis in the sediments of a coastal upwelling regime (NW Africa): Implications for the paleoceanographic record
A biogeochemical study of recent (multicores) sediments of the northwest African slope was undertaken to understand how the sediment composition varies with respect to the location of core sites relative to the centers of coastal upwelling, and how this has affected the palaeoceanographic record. Sedimentary organic carbon contents are inversely correlated with the nitrogen isotopic composition (15N), high Corganic concentrations and low 15N occurring at proximal (shallow) sites and the opposite at distal (deep) ones. These spatial differences are interpreted to result from higher relative nutrient utilization and a decrease in production as waters are advected offshore from the zone of upwelling. Highest Corganic contents also correlate positively with highest concentrations of redox-sensitive elements (U, Mo and S) that are fixed diagenetically in the sediments. These results suggest that the sedimentary regime at a fixed position depends on the spatial location of the productive areas relatively to a given core site. Downcore records of Zr/Al, Ti/Al, mean grain size of the terrigenous fraction, 15N, Corganic , biogenic Ba, U, Mo and sulfur at a single site on the slope are interpreted to reflect glacial-interglacial changes in the core location relative to the coastline (sea-level effect), and hence changes in production as the area of coastal upwelling moved on- and offshore as sea-level changed, as well as undoubtedly changes in upwelling intensity through wind forcing. Further studies are needed to fully understand the interrelationships of all these processes, which are required for building more reliable paleoceanographic-paleoclimatic records.
(Journal of marine research. vol. 58, n° 0022-2402, pp. 5, 809-835, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UBC EOAS, UBC, ISTO, INSU - CNRS, UO, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Seasonal changes in macrophyte and macrozoobenthos assemblages in three coastal lagoons under varying degrees of eutrophication
The dynamics of macrophytic and macrozoobenthic communities were studied during two consecutive years in three French lagoons with differing degrees of eutrophication: (1) Arcachon Bay, a macrotidal lagoon on the Atlantic coast; (2) the fishponds of Certes, an almost enclosed system adjacent to Arcachon Bay; and (3) the Etang du Prévost, a highly eutrophic Mediterranean lagoon experiencing summer dystrophic crises. Two stations were sampled seasonally in each system. The intertidal area of Arcachon Bay was covered by a dense, stable seagrass (Zostera noltii) bed. In terms of abundance, macrofauna were dominated by oligochaetes, which could be related to the high below-ground plant biomass, including slow-decaying debris; faunal biomass remained relatively constant, throughout the study period. In the Certes lagoons, which were intermediate between the other two systems in terms of eutrophication, vegetation was dominated by another rooted phanerogam (Ruppia cirrhosa) with fairly constant biomass, while sporadic development of green macroalgae occurred in spring; both biomass and species richness of macrofauna were low. In the Prévost lagoon, macrophytes were opportunistic macroalgae that first proliferated and then disappeared over a short period in summer; this seasonal crisis resulted in a marked decrease in both biomass and abundance of macrozoobenthos. Macrobenthic dominance shifted after the first summer from suspension-feeding bivalves to subsurface deposit-feeding annelids. The differences in structure and seasonal dynamics of benthos in the three systems may have significant effects on higher trophic levels
(ICES Journal of Marine Science. vol. 57, n° 1054-3139, pp. 1495-1506, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A high-resolution time-series analyses of particle fluxes in the Northern Benguela coastal upwelling system: carbonate record of changes in biogenic production and particle transfer processes
Fluxes of biogenic particles at the shelf edge off Walvis Bay, Namibia, are investigated from a time-series sediment trap in order to evaluate the response of biogenic production to rapid changes in the dynamics of the upwelling process, as well as the importance of particle transfer processes on the nature of sediments accumulating at a high rate on the Namibian margin. Total mass flux displays a smooth trend of lowered values from the start to the end of the experiment despite evidence, from the SST and wind records, of a variable pattern of upwelling dynamics. Contributions of the various biogenic components (carbonates, opal, organic matter) to the total mass flux were relatively constant throughout the period of trapping, suggesting that changes in upwelling dynamics have no obvious implications on the nature of biogenic particles sedimenting at the trap location. A detailed examination of the carbonate fraction indicates a partitioning of its various contributors (coccolithophores and planktonic foraminifera) in terms of sources and mechanisms of transfer to depth. From these data, it is suggested that the bulk of the biogenic particles sedimenting on the slope is resuspended material from the outer shelf, and conversely that direct input from surface waters does not contribute to a high extent to the particle flux at depth. A highly partitioned, three-dimensional flow field is proposed to explain the observed pattern of particle flux as well as the suggested transfer processes affecting the biogenic components.
(Deep Sea Research Part II: Topical Studies in Oceanography. vol. 47, n° 0967-0645, pp. 1999-2028, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The Fetch experiment; a study of atmosphere-ocean fluxes in the Golfe du Lion
The Fetch experiment took place in March-April 1998 in the Golfe du Lion (Mediterranean sea) and was carried out by French and international scientists. Its objectives were to study the exchanges at the air-sea interface, oceanic circulation on the medium scale and the improvement in the use of remote-sensing to estimate wind, waves and fluxes at the sea surface. The special conditions to be found in the experimental area (strong local winds like the Mistral and Tramontane, the presence of the Liguro-Provençal current andsmall extent of the continental shelf) had to be taken into account when the detailed objectives and the strategy were defined. In this paper we summarize the objectives of the experiment, means used and give preliminary results.
(La Météorologie. vol. 29, n° 0026-1181, pp. 14-31, 21/02/2026)
CETP, UVSQ, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS, LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, SA, UVSQ, UPMC, INSU - CNRS, CNRS, LOS, IFREMER, CNRM, INSU - CNRS, CNRS, Comue de Toulouse