Early diagenesis of trace metals (Cd, Cu, Co, Ni, U, Mo, and V) in the freshwater reaches of a macrotidal estuary
Vertical profiles from the water column, including the maximum turbidity zone (MTZ) to the consolidated sediment were sampled in September 2000 in the freshwater reaches of the Gironde Estuary during a complete neap tide-spring tide cycle. The vertical distributions of dissolved major redox parameters and metals (Mn, Fe, Cd, Cu, V, Co, Ni, Mo, and U) were determined. Reactive particulate metal fractions were also determined from selective leaching. The studied system is characterized by density layers functioning at different time-scales, consisting of two mobile layers, i.e., the liquid (LM) and the soft mud (SM), overlying consolidated sediments (CS). This results in a three-zone diagenetic regime where (1) O2 dynamics are fast enough to show depletion in the rapidly mixed LM sequence (tidal time-scale), (2) denitrification occurs on the weekly time-scale mixing SM sequence, and (3) the Mn, Fe, and sulfate cycling occurs in the CS layer (annual time-scale). The studied trace metals show differential behavior during early diagenesis: (1) Cd, Cu, and V are released into pore water preferentially from organic matter in the SM, (2) Co, Ni, and U are released in the CS from Mn and Fe oxides during reductive dissolution, and (3) Mo from both processes. Transient conditions (i.e., oscillations of redox fronts and reoxidation processes), due to the dynamics of the mobile layers, strongly influence the trace metal distributions as inducing resolubilization (Cd, Cu, and Mo). In the CS, authigenic metal phases accumulate, either by direct precipitation with sulfides (Cu, Cd) or co-precipitation with Fe-sulfides (Mo). Microbially mediated reduction of Fe oxides is proposed to control U removal from pore water by reduction of U(VI) to U(IV) at depth. However, a significant fraction of the trace metals is trapped in the sediment in exchangeable forms, and therefore is susceptible to be mobilized due to resuspension of estuarine sediment during strong river flood periods and/or dredging activities.
(Geochimica et Cosmochimica Acta. vol. 70, n° 0016-7037, pp. 2264-2282, 01/05/2006)
LMTG, UT3, Comue de Toulouse, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The western part of the Gulf of Cadiz: contour currents and turbidity currents interactions
Recent multibeam bathymetry and acoustic imagery data provide a new understanding of the morphology of the western part of the Gulf of Cadiz. The gulf is under the influence of a strong current, the Mediterranean Outflow Water (MOW). This current is at the origin of the construction of the giant Contourite Depositional System. Canyons and valleys with erosive flanks are observed. Only the Portimao Canyon is presently connected to the continental shelf. Channels occur on the continental shelf but are presently disconnected from the deeper network of channels and valleys. Slumps are localized in steep slope areas. They are caused by oversteepening and overloading, sometimes probably associated with earthquake activity. Slumps transform sharply into turbidity currents, depositing turbidites on the floor of deep valleys. Interaction of the MOW and gravity currents is suggested by the filling of the incisions located on the drifts below the present seafloor, the shifting of valleys and canyons in the direction of the MOW flow inducing an unusual phenomenon of capture of submarine valleys.
(Geo-Marine Letters. vol. 26, n° 0276-0460, pp. 31-41, 03/02/2006)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Interaction between zinc and freshwater and marine diatom species: Surface complexation and Zn isotope fractionation
This work is devoted to characterization of zinc interaction in aqueous solution with two marine planktonic (Thalassiosira weissflogii = TW, Skeletonema costatum = SC) and two freshwater periphytic species (Achnanthidium minutissimum = AMIN, Navicula minima = NMIN) by combining adsorption and electrophoretic measurements with surface complexation modeling and by assessing Zn isotopes fractionation during both long term uptake and short term adsorption on diatom cells and their frustules. Reversible adsorption experiments were performed at 25 and 5 °C as a function of exposure time (5 min to 140 h), pH (2 to 10), zinc concentration in solution (10 nM to 1 mM), ionic strength (I = 0.001 to 1.0 M) and the presence of light. While the shape of pH-dependent adsorption edge is almost the same for all four species, the constant-pH adsorption isotherm and maximal Zn binding capacities differ by an order of magnitude. The extent of adsorption increases with temperature from 5 to 25 °C and does not depend on light intensity. Zinc adsorption decreases with increase of ionic strength suggesting competition with sodium for surface sites. Cell number-normalized concentrations of sorbed zinc on whole cells and their silica frustules demonstrated only weak contribution of the latter (10 20%) to overall zinc binding by diatom cell wall. Measurements of electrophoretic mobilities (?) revealed negative diatoms surface potential in the full range of zinc concentrations investigated (0.15 760 ?mol/L), however, the absolute value of ? decreases at [Zn] > 15 ?mol/L suggesting a change in surface speciation. These observations allowed us to construct a surface complexation model for Zn binding by diatom surfaces that postulates the constant capacitance of the electric double layer and considers Zn complexation with carboxylate and silanol groups. Thermodynamic and structural parameters of this model are based on previous acid base titration and spectroscopic results and allow quantitative reproduction of all adsorption experiments. Although Zn adsorption constants on carboxylate groups are almost the same, Zn surface adsorption capacities are very different among diatom species which is related to the systematic differences in their cell wall composition and thickness. Measurements of Zn isotopic composition (66Zn/(64Zn)) performed using a multicollector ICP MS demonstrated that irreversible incorporation of Zn in cultured diatom cells produces enrichment in heavy isotope compared to growth media (?66Zn(solid solution) = 0.27 ± 0.05, 0.08 ± 0.05, 0.21 ± 0.05, and 0.19 ± 0.05? for TW, SC, NMIN, and AMIN species, respectively). Accordingly, an enrichment of cells in heavy isotopes (?66Zn(solid solution) = 0.43 ± 0.1 and 0.27 ± 0.1? for NMIN and AMIN, respectively) is observed following short-term Zn sorption on freshwater cells in nutrient media at pH ? 7.8. Finally, diatoms frustules are enriched in heavy isotopes compared to solution during Zn adsorption on silica shells at pH ? 5.5 (?66Zn(solid solution) = 0.35 ± 0.10?). Measured isotopes fractionation can be related to the structure and stability of Zn complexes formed and they provide a firm basis for using Zn isotopes for biogeochemical tracing.
(Geochimica et Cosmochimica Acta. vol. 70, n° 0016-7037, pp. 839-857, 01/02/2006)
LMTG, UT3, Comue de Toulouse, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
ENSO and interdecadal climate variability over the last century documented by geochemical records of two coral cores from the South West Pacific
The south west Pacific is affected by climatic phenomena such as ENSO (El Niño Southern Oscillation) or the PDO (Pacific Decadal Oscillation). Near-monthly resolution calibrations of Sr/Ca, U/Ca and d18Oc were made on corals taken from New Caledonia and Wallis Island. These geochemical variations could be linked to SST (sea surface temperature) and SSS (sea surface salinity) variations over the last two decades, itselves dependent on ENSO occurrences. On the other hand, near-half-yearly resolution over the last century smoothes seasonal and interannual climate signals, but emphasizes low frequency climate variability.
(Advances in Geosciences. vol. 6, n° 1680-7340, pp. 27, 09/01/2006)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PALEOTROPIQUE
Modélisation du courant sagittal induit par les vagues au-dessus des systèmes barre/baïne de la côte aquitaine (France)
Modelling of a rip current induced by waves over a ridge and runnel system on the Aquitanian Coast, France. The spectral wave driver SWAN is coupled with the time- and depth-averaged (2DH) coastal area model MORPHODYN. This coupled model is used to simulate the rip current induced by breaking waves over ridge and runnel systems on the French Aquitanian Coast. Simulations lead to a description of the rip current characteristics and the physical mechanisms leading to its formation. The rip current is controlled by the local bathymetry, the tide level and offshore wave conditions. The presence of this rip current is favoured by shore-normal incidence and long-period swells. During low-energy conditions, the maximum rip current velocity occurs at midtide. For higher energy conditions, the maximum rip velocity sweeps to high tide. The residual forcing notion enables to explain and to highlight this tidal modulation and the rip current formation mechanisms
(Comptes Rendus. Géoscience. vol. 338, n° 1631-0713, pp. 711-717, 01/01/2006)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
cDNA cloning and gene expression of ribosomal S9 protein gene in the mollusk Corbicula fluminea: A new potential biomarker of metal contamination up-regulated by cadmium and repressed by zinc
Biological indicators can be used to assess polluted sites, but their success depends on their specificity. The aim of the present study was to identify a specific cadmium biomarker of the freshwater bivalve Corbicula fluminea. Differential display technique was used to identify new molecular indicators for cadmium exposure. Gene expression of C. fluminea transplanted into a cadmium- and zinc-contaminated river was compared to gene expression of bivalves from a reference site. One differentially expressed band was identified, and the entire cDNA sequence coding for the ribosomal protein S9 (rpS9) was cloned. The rpS9 gene expression was studied by real-time reverse transcription-polymerase chain reaction. After controlled cadmium (15 microg/L) and/or zinc (1 mg/L) laboratory contaminations of the bivalves, this gene was shown to be up-regulated by cadmium and down-regulated by zinc. A 48-d transplantation of animals into a polymetallic field contamination in the Lot river basin (Midi-Pyrénées region, France) showed that rpS9 gene regulation was correlated with the fluctuating cadmium and zinc water contents. To our knowledge, the existence of a gene that is up-regulated by cadmium and repressed by zinc is demonstrated here for the first time.
(Environmental Toxicology and Chemistry. vol. 25, n° 0730-7268, pp. 527, 01/01/2006)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Modélisation du festonnage des barres sableuses d'avant-côte : application à la côte aquitaine, France
Modeling of crescentic pattern development of nearshore bars: Aquitanian Coast, France. Nearshore crescentic bars play key role in nearshore morphodynamics. These bars are observed all along the Aquitanian Coast, with a mean wavelength of about 700 m. A non-linear stability analysis is undertaken to simulate the development of crescentic patterns. Results show that self-organization mechanism can lead alone to the development of these alongshore rhythmic features. Simulated wavelengths are in agreement with observations on the Aquitanian Coast.
(Comptes Rendus. Géoscience. vol. 338, n° 1631-0713, pp. 795-801, 01/01/2006)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMB, UB, Bordeaux INP, CNRS
A surface complexation model for cadmium and lead adsorption onto diatom surface
This work is devoted to the physico-chemical study of cadmium and lead interaction with diatom–water interfaces for two marine planktonic (Thalassiosira weissflogii = TW, Skeletonema costatum = SC) and two freshwater periphytic species (Achnanthidium minutissimum = AMIN, Navicula minima = NMIN) by combining adsorption measurements with surface complexation modeling. Reversible adsorption experiments were performed at 20 °C after 3 h of exposure as a function of pH, metal concentration in solution, and ionic strength. While the shape of pH-dependent adsorption edge is similar among all four diatom species, the constant-pH adsorption isotherm and maximal binding capacities differ. These observations allowed us to construct a surface complexation model for cadmium and lead binding by diatom surfaces that postulates the constant capacitance of the electric double layer and considers Cd and Pb complexation with mainly carboxylic and, partially, silanol groups. Parameters of this model are in agreement with previous acid–base titration results and allow quantitative reproduction of all adsorption experiments.
(Journal of Geochemical Exploration. vol. 88, n° 0375-6742, pp. 110-113, 01/01/2006)
LMTG, UT3, Comue de Toulouse, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
3D-fluorescence spectroscopic analysis of HPLC fractionated estuarine fulvic and humic acids
Six estuarine fulvic (FA) and humic acids (HA) were fractionated with reversed-phase high performance liquid chromatography in a water/acetonitrile gradient, with fluorescence detection. Differences between FA and HA chromatograms pointed to a higher incidence of hydrophobic components in the latter. Excitation-emission matrix fluorescence diagrams of most fractions were similar to those of the bulk samples indicating that, in spite of their distinct polarities, the complexity and main spectral characteristics of the materials persisted. A primary group of fluorophores, which are present in most of the fractions, seems to be at the origin of the fluorescence properties of both kinds of HS. A bathochromic shift of the bulk solutions spectra in relation to the fraction emissions was attributed to a greater proximity of these fluorophores, possibly due to the formation of aggregates. Generally, the results reinforced concepts that humic macromolecules consist of assemblages of structurally similar building blocks. \textcopyright 2006 Sociedade Brasileira de Qu\'imica.
(Journal of the Brazilian Chemical Society. vol. 17, n° 0103-5053, pp. 113--124, 09/04/2026)
UCS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Spatial distribution of zooplankton size spectra on the French continental shelf of the Bay of Biscay during spring 2000 and 2001
During two cruises in springtime (18 March to 13 April 2000 and 27 March to 4 June 2001), the whole French continental shelf of the Bay of Biscay was sampled to obtain an overview on the zooplankton community size structure. A laboratory optical plankton counter (OPC-1L) was used to process plankton net tow samples and estimate abundance, biovolume, and general characteristics of size spectra. In a second step, biomass estimates were extrapolated from size by using a conversion factor. Both biomass and abundance estimates show spatial patterns with a clear coastal-open sea gradient for both years. The coastal area was characterized by the highest biomasses and abundances per volume. A first analysis of the zooplankton community size spectra was made by using the slope of the normalized biomass size spectrum. Different spatial patterns of zooplankton size spectra were highlighted for spring 2000 and 2001. The highest slopes were found for the coastal zone, showing a large ratio of small organisms, although this was less marked in the springtime 2000. Stations characterized by high proportions of large organisms were located in majority in the north of the bay and at the shelf break. A second analysis using the size probability distributions of organisms revealed a nearly permanent nonlinearity of probability distributions. This implied the community structure was not in an equilibrium state during spring and this nonlinearity could be locally related to dominant species dynamics.
(Journal of Geophysical Research. Oceans. vol. 111, n° 2169-9275, 09/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOPB, INSU - CNRS, CNRS