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, 23/10/2026)
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
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, 23/10/2026)
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, 23/10/2026)
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
Interactions between metal oxides and species of nitrogen and iodine in bioturbated marine sediments
By using a gold amalgam (Au/Hg) voltammetric microelectrode, we have measured simultaneously and with millimeter resolution the distributions of O 2, Mn(II), Fe(II), I(-I), and HS(-I) in bioturbated sediment cores from the Laurentian Trough. We also measured nitrate and ammonia in the pore water, total I and ascorbate- and HCl-extractable Fe and Mn in the solid-phase sediment, and fluxes of O 2, NO 3-, and NH 4+ across the sediment-water interface. The concentrations of O 2 and Mn(II) were below their respective detection limits of 3 and 5 μM between 4 and 12 mm depth, but a sharp iodide maximum occurred at the depth where upward diffusing Mn(II) was being removed. We propose that the iodide peak is maintained through the reduction of IO 3- by Mn(II), reoxidation of I(-I) to IO 3- in the oxic zone above the peak and oxidation to I 2 below where it is ultimately trapped by reaction with organic matter. The iodide production rate is sufficient to account for the oxidation of all of the upward diffusing Mn(II) by IO 3-. Nitrate plus nitrite (ΣNO 3) decreased to a minimum within 10 mm of the sediment-water interface, in agreement with flux measurements which showed ΣNO 3 uptake by the sediment. Below the minimum, ΣNO 3 rebounded, and reached a maximum at 40- to 50-mm depth. This rebound is attributed to the anaerobic oxidation of ammonia by manganese oxides. Fe(II) was always first detected below the anoxic ΣNO 3 maximum, and was accompanied by colloidal or complexed Fe(III). A sharp upward-directed ammonia gradient was recorded near the sediment-water interface, but no ammonia was released during the first 48 h of the incubations. If the ammonia removal were due to coupled bacterial nitrification-denitrification, more than one half of the total measured oxygen uptake (6.7 to 7.3 mmol/m 2/d) would be required, and more organic carbon would be oxidized by nitrate than by oxygen. This scenario is not supported by nitrate flux calculations. Alternatively, the oxidation of ammonia to N 2 by manganese oxides is a potential removal mechanism. It would require one quarter of the total oxygen flux. The high-resolution profiles of redox species support the conceptualization of bioturbated sediments as a spatially and temporally changing mosaic of redox reactions. They show evidence for a multitude of reactions whose relative importance will vary over time, and for reaction pathways complementing those usually considered in diagenetic studies.
(Geochimica et Cosmochimica Acta. vol. 64, n° 0016-7037, pp. 2751-2763, 23/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
La faune interstratifiée dans les gypses Messiniens de Los Yesos (bassin de Sorbas, SE Espagne): implications
De récentes investigations menées sur les niveaux fossilifères interstratifiés dans les gypses messiniens de Los Yesos (bassin de Sorbas, Andalousie) ont permis la récolte d'une macrofaune et d'une microfaune marines diversifiées avec au total plus de 80 espèces identifiées représentant principalement des bivalves, des échinides, des foraminifères, des ostracodes, des crustacés décapodes et des bryozoaires... L'assemblage est caractéristique d'un milieu de plate-forme de type infralittoral inférieur ~ circalittoral supérieur. Sur le plan stratigraphique, la faune présente un net cachet messinien, mais contient des espèces qui survivront du Pliocène ~ l'Actuel au sein du bassin méditerranéen. Ces résultats pèsent de nouveau le problème de l'influence réelle de la crise messinienne sur les peuplements littoraux méditerranéens.
(Geobios, n° 0016-6995, pp. 13, 23/10/2026)
MNHN, UPMC, CNRS, GR, UR, INSU - CNRS, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS, GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, CNRS
Contribution to a synopsis of marine species richness in the Pertuis Charentais Sea with new insights in soft-bottom macrofauna of the Marennes-Oléron Bay
The catalogue of soft-bottom macrofauna in the Marennes-Oléron Bay (French Atlantic coast) has been updated from a benthic survey conducted in April-May 1995. 262 stations were selected using a stratified random strategy based on sediment types and bathymetric levels. 231 soft-bottom macrofauna species were identified. A synopsis of all available literature since the first local marine study published in 1710 by Antoine Ferchauld de Réaumur indicated that 60 benthic species were reported in the Marennes-Oléron Bay for the first time. The sampling effort, i.e. more than 1 station per km2 and size of the sieving square mesh (1 mm), can partially explain these results. Most of the new recorded species were crustaceans (28 species) and polychaete annelids (25 species) for only five molluscs. First report of Ocinebrellus inornatus, Mollusca Gastropoda, should be noted for the European Atlantic coasts. Additionally, alteration of subtidal habitats, colonized by Crepidula fornicata Linnaeus (Mollusca, Gastropoda) since the 1970's, may also have facilitated the recruitment and spread of some annelid polychaetes which were not previously reported in the Marennes-Oléron Bay. The total number of macrofauna species in the Pertuis Charentais Sea is 858.
(Cahiers de Biologie Marine. vol. 41, n° 0007-9723, pp. 181-222, 23/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
Dissolved organic matter fluorescence spectroscopy as a tool to estimate biological activity in a coastal zone submitted to anthropogenic inputs
Here we report on an investigation of the three-dimensional excitation-emission-matrix (EEM) fluorescence spectra of unconcentrated water samples collected in 1996, 1998 and 1999 at a site particularly propitious for macro-algae development. The degradation of these macro-algae was studied to determine the influence of their exudates on natural water EEM fluorescence spectra. This work demonstrates that biological activity is one of the major factors involved in the formation of the blue-shifted fluorescence band observed in marine waters (β component Ex/Em = 310-320 nm/380-410 nm); our study also shows that fluorescence can be used to evaluate the biological activity both quantitatively and to determine its different phases. \textcopyright 2000 Elsevier Science Ltd.
(Organic Geochemistry. vol. 31, n° 0146-6380, pp. 1765--1781, 23/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The proliferating Gastropoda Crepidula fornicata may stimulate macrozoobenthic diversity
Since the late 19th century, the accidentally introduced Gastropoda Crepidula fornicata has been invading sheltered coastal waters of western Europe. The consequences of this proliferation on macrozoobenthic communities were studied in the Bay of Marennes-Oléron, France. Crepidula fornicata was found in a wide range of sediment grain sizes and depths, with however, a predilection for shallow muddy areas where abundance and biomass reached 4770 ind m−2 and 354 g DW m−2, respectively. Soft-sediment macrofaunal assemblages were compared in similar habitats, in the presence and absence of C. fornicata. In muddy and medium sand areas, abundance, biomass and species richness of macrofauna were generally greater in presence of C. fornicata, with Annelida dominating, although the differences were significant (P<0.05) only in one location out of five. The species composition was moderately different in the presence of C. fornicata. In coarse sand, the abundance of C. fornicata was low and did not affect abundance, biomass and species richness of the macrofauna. However, species composition differed where C. fornicata was absent, with a higher proportion of mobile Crustaceana. The effect of C. fornicata on benthic communities differs in relation to the habitat they colonize: in muddy sediments, the presence of C. fornicata apparently stimulates zoobenthic community diversity and abundance (mostly deposit-feeders), whereas in coarser sediments, macrofauna community is different (more suspension-feeders) from the community associated with C. fornicata.
(Journal of the Marine Biological Association of the United Kingdom. vol. 79, n° 0025-3154, pp. 1069-1077, 01/12/1999)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
Présentation du logiciel SnB ( Shake and Bake ) Exemples d'applications
On présentera le principe de fonctionnement du programme de résolution de structures cristallographiques par méthode directe SnB (Shake and Bake) développé par une équipe de l'Université de Buffalo. Des exemples d'application aux petites protéines seront donnés, ainsi qu'à deux structures d'antibiotiques résolues au LMCP grâce à SnB. A cette occasion on passera rapidement en revue les caractéristiques de ces Pristinamycines.
(26/11/1999)
LMCP, UPMC, UPD7, IPG Paris, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Anomalous directions of the natural remanent magnetization in Late Pleistocene marine sediments from the coast of Mauritania (West Africa)
(Physics of the Earth and Planetary Interiors. vol. 115, n° 0031-9201, pp. 81-100, 01/09/1999)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEOTRAC, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS