Nitrogen isotopic evidence for deglacial changes in nutrient supply in the eastern equatorial Pacific
The Eastern Equatorial Pacific (EEP) is a high nutrient-low chlorophyll region of the ocean. Downcore nitrogen isotope records from the EEP have been previously interpreted as a direct reflection of changes in nutrient consumption. However, the observed changes in sedimentary d 15 N since the last glacial maximum have no coherent relationship with export productivity or an inferred variation in the iron-to-nitrate ratio of the surface waters. Rather, downcore N isotope records in the EEP strongly resemble changes in the extent of water column denitrification as recorded in nearby sedimentary d 15 N records along the western margin of the Americas. This similarity is attributed to the overprinting of the N isotopic composition of nitrate in the EEP through the advection of nitrate westward from the margins in the subsurface. A local nitrogen isotope record of changes in the degree of nutrient consumption is extracted from the bulk sedimentary record by subtracting two different sedimentary d 15 N records of denitrification changes from two new EEP d 15 N records (TR163-22 and ODP Site 1240). The denitrification records used are from 1) the Central American margin (ODP Site 1242) and 2) the South American margin (GeoB7139-2). The degree of consumption in the surface waters declines rapidly from elevated values during the last glacial maximum to a pair of minima around 15 and 11-13 ka, and finally it increases into the Holocene. The derived EEP nitrogen isotope record indicates that the regional peak in export productivity occurred when the supply of nutrients exceeded the apparently high demand. The influx of nutrients during the deglaciation is attributed to the resumption of intense overturning in the Southern Ocean and the release of sequestered CO 2 and nutrient-rich, O 2 poor waters from the deep ocean. This has important implications for understanding the glacial-interglacial scale variation in intermediate water suboxia and water column denitrification.
(Paleoceanography. vol. 24, n° 0883-8305, 01/12/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A 1.2Ma record of glaciation and fluvial discharge from the West European Atlantic margin
(Quaternary Science Reviews. vol. 28, n° 0277-3791, pp. 2974-2981, 01/12/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER, CAM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
A 1.2Ma record of glaciation and fluvial discharge from the West European Atlantic margin
The correlation of continental sedimentary records with the marine isotope stratigraphy is a challenge of central importance in Quaternary stratigraphy, particularly in Western Europe where long records of glaciation on land areas are particularly rare. Here we demonstrate for the first time the interrelationship of events during the last 1.2 Ma in an ocean-sediment core from the Bay of Biscay (NE Atlantic), SW of the Channel. The identification of discharge variations from tributary river systems to the ‘Fleuve Manche’ palaeoriver during glacio-eustatic sea-level lowstands demonstrates the correlation of the marine sediment stratigraphy to the expansion and recession of the European ice-sheets. The amplitude and chronology of European ice-sheet oscillations since the late Early Pleistocene is discussed and our results demonstrate that the first coalescence of the Fennoscandian and British ice-sheets in the North Sea basin ca 450 ka ago caused a profound change in lowstand European drainage alignment. This change caused a rerouting of Fennoscandian and eastern British ice-sheets-derived meltwaters from northwards into the Nordic Seas to southwards into the eastern North Atlantic thereafter. Besides allowing a thorough synchronisation of the European ice-sheet palaeogeography with the well-dated records of palaeoceanographical changes, our results improve the stratigraphy of the English Channel palaeovalleys and will provide important constraints on paleoclimatic scenarios considering the impact that such rerouting and meltwater surges might have on the stability of the oceanic conveyor belt.
(Quaternary Science Reviews. vol. 28, n° 0277-3791, pp. 2974 - 2981, 01/12/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER, CAM, LSCE, CEA, CNRS
Cadmium-Induced genotoxicity in zebrafish at environmentally relevant doses
Genotoxic effects of cadmium on zebra fish Danio rerio have been assessed by random amplified polymorphic DNA and real time PCR, followed by a comparison of the melting temperature patterns between each amplification reaction. Fish were exposed to two concentrations of cadmium chloride dissolved in the medium (1.9+/-0.6 microg Cdl(-1), C(1); 9.6+/-2.9 microg Cdl(-1), C(2)) for 21 days. A discriminative RAPD probe, OPB11, was first selected producing differential band patterns between control and metal-exposed genomic DNAs. RAPD-PCR showed an increase in the relative hybridization efficiency of OPB11 on the genomic DNAs coming from fish exposed to both Cd concentrations as compared to the control condition. In addition, the RAPD-PCR melting temperature patterns showed that with the OPB11 probe, the frequency of PCR products whose fusion temperature belongs to the [86-87 degrees C] interval decreased with Cd contamination, whereas an increase of frequency for the [78-80 degrees C] and [85-86 degrees C] intervals was correlated with Cd exposure.
(Ecotoxicology and Environmental Safety. vol. 73, n° 0147-6513, pp. 312-319, 01/11/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A system dynamics model for the management of the Manila clam, Ruditapes philippinarum (Adams and Reeve, 1850) in the Bay of Arcachon (France)
The Manila clam Ruditapes philippinarum (Adams and Reeve, 1850) is one of the mollusc species that, driven mainly by the shellfish market industry, has extended throughout the world, far beyond the limits of its original habitat. The Manila clam was introduced into France for aquaculture purposes, between 1972 and 1975. In France, this venerid culture became increasingly widespread and, since 1988, this species has colonised most of the embayments along the French Atlantic coast. In 2004, this development resulted in a fishery of ca. 520 t in Arcachon Bay.
(Ecological Modelling. vol. 220, n° 0304-3800, pp. 2828-2837, 01/11/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The magnetic fraction: A tracer of deep water circulation in the North Atlantic
(Earth and Planetary Science Letters. vol. 288, n° 0012-821X, pp. 444-454, 01/11/2009)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIMAG, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A large-scale laboratory experiment of rip current circulations over a moveable bed: drifter measurements
The present paper presents a laboratory experiment of rip current circulations over a moveable bed. The rip current characteristics over four distinct beach morphologies, exhibiting more or less developed nature-like bar-rip morphology,were investigated. For each video run, the same off shore shore-normal waves were generated by the wave maker with the same mean water level in order to study the sensitivity of the rip current characteristics as a function of the beach morphology only. In each case, a 1-hour video run was used to track a large number (~30) of drifters released within the surf zone. Image coordinates were then rectifie d to still water level Cartesian coordinates to compute drifter velocities, mean characteristics and surf zone rete ntion rates. Results show the presence of classic rip current patterns with counter-rotating cells and a relatively narrowoffshore-directed jet with, for three of the situations, a reasonably symmetric shape. Non-surprisingly, it was found that rip current intensity increases with increasing relative depth of the rip channel. The wave-driven circulations were strongly unstable. Computed standard deviation in fl ow intensity and direction provides high resolution information on the spatial variability of the rip current insta bilities with, for instance, highly-pulsating and weakly directionally variable offshore-directed flow in the rip channel. Conversely to what was previously hypothesized in the literature, there was hardly trace of vortices being shed offs hore and drifters exiting the surf zone compartment were not systematically caught by a pulsating jet. The cause for drifter exiting the semi-enclosed surf zone compartment remains, however, elusive and deserves further investigations. The computed surf zone retention rates (~90%) were of the order of those previously observed in the field, with no clear relationship with the mean rip current velocity or relative depth of the rip channel. Further video-runs will have to be analyzed to explore potential explanations.
(01/10/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGI, UJF, Grenoble INP, CNRS, UAG, INSU - CNRS, UM, CNRS, IRPHE, AMU, ECM, CNRS, LSEET, INSU - CNRS, UTLN, CNRS
What forced the collapse of European ice sheets during the last two glacial periods (150 ka BP and 18 ka cal BP)? Palynological evidence
We present a new marine palynological record from the temperate North-eastern Atlantic (core MD03-2692, Celtic-Armorican margin) in the area of influence of the 'Fleuve Manche' paleoriver during glacial times. The runoff of this paleoriver was connected to the glacial history of European ice sheets (including the British Irish Ice Sheet-BIIS). Our study conducted on dinoflagellate cysts assemblages over the last 200 ka, associated with quantification of palynological remains reflecting continental influence (pre-Quaternary dinocysts and micro-algae Pediastrum spp. coenobia), yields detailed insights into the sea-surface paleoenvironments of this sector. More specifically, mechanisms responsible for the origin of unusual deposits of laminated sequences found at the end of Marine Isotope Stage (MIS) 2 and within mid-MIS 6 are here constrained. We provide evidence of genetic similarities between fluvial discharges occurring before and during times of deposition of the laminated deposits. Our study clarifies the causes of the collapse of European glaciated systems. At the end of MIS 2, prior to the deposition of the laminated deposits, pleni-oceanic influence characterized by high concentrations of Quaternary dinocysts prevailed, and a dinocyst species tracing the penetration of the warm North Atlantic Drift into the Bay of Biscay is recorded. However, this scenario did not recur prior to the deposition of laminated sediments of mid-MIS 6. In addition, contrary to the laminated deposits found at the end of MIS 2 and directly associated with Termination I, MIS 6 laminae appeared 20 ka earlier than Termination II. Our work shows that, during the penultimate glacial stage, the collapse of mid-latitudes ice sheets around 170 ka B.P. may have immediately followed the MIS 6.5 warming phase. Then, the most important melting event around 150 ka B.P. may be linked to a peak in insolation at 65°N, though less important than those during MIS 6.5 and Termination II.
(Palaeogeography, Palaeoclimatology, Palaeoecology. vol. 281, n° 0031-0182, pp. 66-78, 01/10/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GM, IFREMER
Observations on the relationship between the Antarctic coastal diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen and sea ice concentrations during the late Quaternary
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(Marine Micropaleontology. vol. 73, n° 0377-8398, pp. 14-25, 01/10/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UP1, LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, VU
Improving estuarine net flux estimates for dissolved cadmium export at the annual timescale: Application to the Gironde Estuary
Dissolved Cd (Cd D) concentrations along the salinity gradient were measured in surface water of the Gironde Estuary during 15 cruises (2001-2007), covering a wide range of contrasting situations in terms of hydrology, turbidity and season. During all situations dissolved Cd concentrations displayed maximum values in the mid-salinity range, reflecting Cd addition by chloride-induced desorption and complexa-tion. The daily net Cd D fluxes from the Gironde Estuary to the coastal ocean were estimated using Boyle's method. Extrapolating Cd D concentrations in the high salinity range to the freshwater end member using a theoretical dilution line produced 15 theoretical Cd concentrations (Cd D 0), each representative of one distinct situation. The obtained Cd D 0 concentrations were relatively similar (w201 AE 28 ng L À1) when freshwater discharge Q was >500 m 3 s À1 (508 Q 2600 m 3 s À1), but were highly variable (340 AE 80 ng L À1 ; 247-490 ng L À1) for low discharge situations (169 Q 368 m 3 s À1). The respective daily Cd D net fluxes were 5-39 kg day À1 , mainly depending on freshwater discharge. As this observation invalidates the existing method of estimating annual Cd D net fluxes, we proposed an empirical model, using representative Cd D 0 values and daily freshwater discharges for the 2001-2007 period. Subsequent integration produced reliable Cd D net flux estimates for the Gironde Estuary at the annual timescale that ranged between 3.8-5.0 t a À1 in 2005 and 6.0-7.2 t a À1 in 2004, depending on freshwater discharge. Comparing Cd D net fluxes with the incoming Cd D fluxes suggested that the annual net Cd D addition in the Gironde Estuary ranged from 3.5 to 6.7 t a À1 , without any clear temporal trend during the past seven years. The annual Cd D net fluxes did not show a clearly decreasing trend in spite of an overall decrease by a factor w6 in Cd gross fluxes during the past decade. Furthermore, in six years out of seven (except 2003), the annual Cd D net fluxes even exceeded river borne total (dissolved þ particulate) gross Cd fluxes into the estuary. These observations were attributed to progressive Cd desorption from both suspended particles and bottom sediment during various sedimentation-resuspension cycles induced by tidal currents and/or continuous dredging (navigation channel) and diverse intra-estuarine sources (wet deposition, urban sources, and agriculture). Provided that gross fluxes remain stable over time, dissolved Cd exportation from the Gironde Estuary to the coastal ocean may remain at the present level for the coming decade and the estuarine sedimentary Cd stock is forecast to decrease slowly.
(Estuarine, Coastal and Shelf Science. vol. 84, n° 0272-7714, pp. 429-439, 01/10/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS