Tidal sands as biogeochemical reactors
(Estuarine, Coastal and Shelf Science. vol. 84, n° 0272-7714, pp. 84-90, 01/08/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Dissolved uranium, vanadium and molybdenum behaviours during contrasting freshwater discharges in the Gironde Estuary (SW France)
Understanding trace metal behaviour in estuarine environments requires sampling strategies and analytical methods adapted to strong physical and geochemical gradients. In this study, we present a specific sampling strategy covering a wide range of hydrological conditions during nine cruises in 2003-2007 to characterise the behaviour of three dissolved metals (uranium, vanadium and molyb-denum) in surface and bottom water along the salinity gradient of the highly turbid macrotidal Gironde Estuary using a solid-liquid extraction. Uranium behaved conservatively whatever the water discharges observed. The slight dissolved U depletion compared to the theoretical dilution line between the fluvial and marine end-members occasionally observed in the low salinity range (0-3) was attributed to the mixing of different water bodies of the Gironde tributaries. In contrast, dissolved V behaviour was largely influenced by the hydrological conditions, showing increasingly pronounced addition with decreasing freshwater discharges, (i.e. increasing residence times of water and particles in the estuary). This addition of dissolved V in the low-to mid-salinity range was attributed to desorption processes observed in the Maximum Turbidity Zone (MTZ). The distribution of dissolved Mo concentrations along the salinity gradient was highly variable. Apparent conservative, and non-conservative behaviours were observed and were related to the concomitance of desorption from SPM, inputs from sediments for additive distribution and biological uptake and removal into sediments for subtractive distribution. Based on the whole database (2003-2007), annual net fluxes to the coastal ocean were estimated for dissolved U (15.5-16.6 t yr À1) and V (31.3-36.7 t yr À1).
(Estuarine, Coastal and Shelf Science. vol. 83, n° 0272-7714, pp. 550-560, 01/08/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Determination of diet in Manila clams by spatial analysis of stable isotopes
Spatial changes in the dietary regime of Ruditapes philippinarum from intertidal sediments of Arcachon Bay were depicted by analyzing stable isotope ratios in both its adductor muscles and potential trophic sources. Manila clams were collected from 50 sites in May to June 2006. Dietary reconstruction was based on the IsoSource mixing model, considering trophic enrichments of 3.5‰ for carbon and 3.0‰ for nitrogen, which were determined experimentally. δ13C and δ15N values, respectively, averaged –28.2 and 5.2‰ for riverine particulate organic matter (POM), –20.6 and 4.7‰ for inner bay phytoplankton, –21.0 and 5.6‰ for outer bay phytoplankton, –16.8 and 4.8‰ for microphytobenthos, –18.4 and 3.9‰ for sedimentary organic matter (SOM) and 11.8 and 4.0‰ for Zostera noltii. Clam muscle δ13C and δ15N values ranged from –20.5 to –16.4‰, and from 7.6 to 9.3‰, respectively. δ15N significantly decreased from southern to northern parts of the bay, while δ13C values increased with tidal elevation. Outer bay phytoplankton was the major diet component of clams. Clams from the southeast mainly incorporated outer bay phytoplankton despite the proximity of the Leyre River, whereas clams from the northwest incorporated approximately equal parts of inner and outer bay phytoplankton, riverine POM, microphytobenthos and SOM. These patterns were consistent with spatial gradients driven by the dominant role of tidal hydrodynamics within the bay and land-use characteristics of the catchment.
(Marine Ecology Progress Series. vol. 387, n° 0171-8630, pp. 167 - 177, 28/07/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS, IFREMER
Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka
mirroring past sea surface hydrological conditions. The maps revealed that the Polar Front presence along the Iberian margin was restricted to Heinrich events. The sea surface conditions during the Last Glacial Maximum were close to those at present day, except for the northern sites which briefly experienced subarctic conditions.
(Geochemistry, Geophysics, Geosystems. vol. 10, pp. n/a-n/a, 01/07/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Wet to dry climatic trend in north-western Iberia within Heinrich events
The direct sea-land correlation applied to core MD99-2331 retrieved from the north-western Iberian margin shows a two-phase pattern within Heinrich events 4, 2 and 1 in the ocean and in the adjacent landmasses. Changes between wet/cold and dry/cool conditions in the Iberian Peninsula detected during these extreme events cannot be explained by a simple oceanographic mechanism related to changes in the strength of the Atlantic Meridional Overturning Circulation. Here we propose an additional atmospheric mechanism able to produce this scenario based on the comparison between the MD99-2331 record and other available palaeoclimate sequences from the North Atlantic region (18-75°N and 0-75°W). The climatic asymmetry observed between mid- and subtropical eastern North Atlantic latitudes (wet/dry) and the Blake Outer Ridge (dry/wet) during H4, H2 and H1 can be explained by changes in the position of the Atlantic jet-stream. During the first phase of H4, H2 and H1 the Atlantic jet-stream was located further south following the southward displacement of the oceanic thermal front as far south as 35°-37°N. On the contrary, during the second phase of H4, H2 and H1 the jet-stream was located further north following the northward displacement of this thermal front as far north as 42°N. From the atmospheric point of view, these two phases are reminiscent of the present-day negative and positive prevailing modes of the North Atlantic Oscillation (NAO), respectively, but high-resolution studies of additional North Atlantic key sites and climate simulations are needed to confirm the hypothesis of a NAO-like mechanism operating on millennial timescales.
(Earth and Planetary Science Letters. vol. 284, n° 0012-821X, pp. 329-342, 01/07/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE, CSNSM, UP11, IN2P3, CNRS, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, WHOI
Timing of massive 'Fleuve Manche' discharges over the last 350 kyr: insights into the European ice-sheet oscillations and the European drainage network from MIS 10 to 2
Continuous high-resolution mass accumulation rates (MAR) and X-ray fluorescence (XRF) measurements from marine sediment records in the Bay of Biscay (NE Atlantic) have allowed the determination of the timing and the amplitude of the 'Fleuve Manche' (Channel River) discharges during glacial stages MIS 10, MIS 8, MIS 6 and MIS 4-2. These results have yielded detailed insight into the Middle and Late Pleistocene glaciations in Europe and the drainage network of the western and central European rivers over the last 350 kyr. This study provides clear evidence that the 'Fleuve Manche' connected the southern North Sea basin with the Bay of Biscay during each glacial period and reveals that 'Fleuve Manche' activity during the glaciations MIS 10 and MIS 8 was significantly less than during MIS 6 and MIS 2. We correlate the significant 'Fleuve Manche' activity, detected during MIS 6 and MIS 2, with the extensive Saalian (Drenthe Substage) and the Weichselian glaciations, respectively, confirming that the major Elsterian glaciation precedes the glacial MIS 10. In detail, massive 'Fleuve Manche' discharges occurred at ca 155 ka (mid-MIS 6) and during Termination I, while no significant discharges are found during Termination II. It is assumed that a substantial retreat of the European ice sheet at ca 155 kyr, followed by the formation of ice-free conditions between the British Isles and Scandinavia until Termination II, allowed meltwater to flow northwards through the North Sea basin during the second part of the MIS 6. We assume that this glacial pattern corresponds to the Warthe Substage glacial maximum, therefore indicating that the data presented here equates to the Drenthe and the Warthe glacial advances at ca 175-160 ka and ca 150-140 ka, respectively. Finally, the correlation of our records with ODP site 980 reveals that massive 'Fleuve Manche' discharges, related to partial or complete melting of the European ice masses, were synchronous with strong decreases in both the rate of deep-water formation and the strength of the Atlantic thermohaline circulation. 'Fleuve Manche' discharges over the last 350 kyr probably participated, with other meltwater sources, in the collapse of the thermohaline circulation by freshening the northern Atlantic surface water.
(Quaternary Science Reviews. vol. 28, n° 0277-3791, pp. 1238-1256, 25/06/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GM, IFREMER, LDO, INSU - CNRS, UBO EPE, CNRS, UEB, UA, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CAM
Multi-disciplinary investigation of fluid seepage on an unstable margin: The case of the Central Nile deep-sea fan.
We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and 230Th/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at ∼ 2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at ∼ 1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (∼ 8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (∼ 1 km2) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since ∼ 5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of 'fossil' carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope
(Marine Geology. vol. 261, n° 0025-3227, pp. 92-104, 01/06/2009)
GM, IFREMER, IMAGES, UPVD, GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, LEP, EEP, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SAE, IRD, UPMC, CNRS, LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, IFREMER, NIOZ
African monsoon enhancement during the penultimate glacial period (MIS 6.5~ 170 ka) and its atmospheric impact
1] A reconstruction of northwest African summer monsoon strength during the cold marine isotopic stage (MIS) 6 indicates a link to the seasonal migration of the Intertropical Convergence Zone (ITCZ). High-resolution studies of eolian dust supply and sea surface temperature recorded in marine core MD03-2705, on the Mauritanian margin, provide a better understanding about the penultimate glacial history of northwestern African aridity/humidity and upwelling coastal activity. Today, site MD03-2705 experiences increased upwelling and dust flux during the winter months, when the ITCZ is in a southerly position. Analyses of foraminifera isotopic composition suggest that during MIS 6.5 (180–168 ka) the average position of the ITCZ migrated north, marked by an increase in the strength of the summer monsoon, which decreased eolian dust transport and the coastal upwelling activity. The northward migration is in phase with a specific orbital combination of a low precessional index with a high obliquity signal. High-resolution analysis of stable isotopes (d 18 O and d 13 C) and microscale resolution geochemical (Ti/Al and quartz grain counts) determinations reveal that the transition between monsoonal humid (MIS 6.5) and dry (MIS 6.4) conditions has occurred in less than 1.3 ka. Such rapid changes suggest a nonlinear link between the African monsoonal rainfall system and environmental changes over the continent. This study provides new insights about the influence of vegetation and oceanic temperature feedbacks on the onset of African summer monsoon and demonstrates that, during the penultimate glacial period, changes in tropical dynamics had regional and global impacts.
(Paleoceanography. vol. 24, n° 0883-8305, pp. n/a-n/a, 01/06/2009)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Comparative analysis of gene expression in brain, liver, skeletal muscles, and gills of zebrafish (Danio rerio) exposed to environmentally relevant waterborne uranium concentrations
The effects of waterborne uranium (U) exposure on gene expression were examined in four organs (brain, liver, skeletal muscles, and gills) of the zebrafish (Danio rerio). Adult male fish were exposed to three treatments: No added uranium (control), 23 ± 6 μg U/L, and 130 ± 34 μg U/L. After 3, 10, 21, and 28 d of exposure and an 8-d depuration period, gene expression and uranium bioaccumulation were analyzed. Bioaccumulation decreased significantly in liver during the depuration phase, and genes involved in detoxification, apoptotic mechanism, and immune response were strongly induced. Among these genes, abcb3l1, which belongs to the adenosine triphosphate (ATP)-binding cassette transporter family, was induced 4- and 24-fold in organisms previously exposed to 23 ± 6 and 130 ± 34 μg U/L, respectively. These results highlight the role of liver in detoxification mechanisms. In gills, at the highest uranium concentration, gpx1a, cat, sod1, and sod2 genes were up-regulated at day 21, indicating the onset of an oxidative stress. Mitochondrial metabolism and DNA integrity also were affected, because cox1, atp5f1, and rad51 genes were up-regulated at day 21 and during the depuration phase. In skeletal muscles, coxI, atp5f1, and cat were induced at day 3, suggesting an impact on the mitochondrial metabolism and production of reactive oxygen species. In brain, glsI also was induced at day 3, suggesting a need in the glutamate synthesis involved with neuron transmission. No changes in gene expression were observed in brain and skeletal muscles at days 21 and 28, although bioaccumulation increased. During the depuration phase, uranium excretion was inefficient in brain and skeletal muscles, and expression of most of the tissue-specific genes was repressed or unchanged. © 2009 SETAC.
(Environmental Toxicology and Chemistry. vol. 28, pp. 1271-1278, 01/06/2009)
IRSN/DEI/SECRE/LRE, IRSN/DEI/SECRE, IRSN, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Benthic indicators and index approaches in the three main estuaries along the French Atlantic coast (Seine, Loire and Gironde)
The three main estuaries in the French Atlantic coast – the Seine, Loire and Gironde, all with high tidal regimes – are interfaces between the continental and the coastal ecosystems. The Seine and Gironde are highly contaminated, whereas the Loire remains in a more natural state. Both the Seine and Gironde have suffered from harbour construction, and as a result, their biological units are extremely compartmentalized. Benthic species and communities have adapted to tolerate temporal physical and chemical changes (e.g. salinity, substrata, depth, and levels of fine particles and oxygen) and human activities (e.g. dredging, shipping traffic, and habitat reduction). Although numerous bio-indicators and indices are used to define the ecological quality status (EcoQS) of coastal waters, very few of them were developed specifically for environments with a mosaic of conditions and salinity levels, including freshwater. The main problem appears to be that all the indices for determining anthropogenic stress examine the abundances of stress-tolerant species, which may also be able to tolerate natural stressors such as those occurring in estuaries. This paper takes a look at the development status of the benthic indicators and index approaches used in the three main estuaries along the French Atlantic coast. In addition, it examines the adaptation of the different benthic indicators to the taxonomic sufficiency principle, and the adaptation of the Benthic Opportunistic Polychaetes Amphipods index (BOPA) and the Benthic Opportunistic Annelida Amphipod index (BO2A) for use in the freshwater zones of transitional waters (i.e. up to the upper limit of the tidal range). Several perspectives are discussed in light of the diverse disturbances and the heterogeneity of such stressed zones, such as the use of multimetric and scoring approaches.
(Marine Ecology. vol. 30, n° 0173-9565, pp. 228-240, 01/06/2009)
LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ