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| Thibault De Chanvalon, A.; Mouret, A.; Knoery, Joel; Geslin, E.; Peron, O.; Metzger, E.. |
| The sampling of surface sediment from two sites of a mudflat of the Loire Estuary during four contrasting seasons has led to new information about geochemical cycling under transient diagenesis fuelled by flood deposition. Based on stocks of reactive iron-oxides and manganese-oxides (ascorbate-extracted) and pore water concentrations, the progressive evolution of flood deposits is described. Three major steps are observed: at first, there is no manganese, iron and phosphorus release into pore water within the flood-deposited layer. Then, during a period of approximately 1 month, Mn oxides are consumed while the dissolved Mn concentration increases. Simultaneously, the Fe oxide-rich layer from flood deposition prevents (or at least limits) phosphorus... |
| Tipo: Text |
Palavras-chave: Flood deposition; Ascorbat extraction; Transient diagenesis; Savitzky Golay filter; RiOMars. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00354/46525/46291.pdf |
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| Pastor, L.; Cathalot, C.; Deflandre, B.; Viollier, E.; Soetaert, K.; Meysman, F. J. R.; Ulses, C.; Metzger, E.; Rabouille, C.. |
| In situ oxygen microprofiles, sediment organic carbon content, and pore-water concentrations of nitrate, ammonium, iron, manganese, and sulfides obtained in sediments from the Rhone River prodelta and its adjacent continental shelf were used to constrain a numerical diagenetic model. Results showed that (1) the organic matter from the Rhone River is composed of a fraction of fresh material associated to high first-order degradation rate constants (11-33 yr(-1)); (2) the burial efficiency (burial/input ratio) in the Rh boolean AND one prodelta (within 3 km of the river outlet) can be up to 80 %, and decreases to similar to 20% on the adjacent continental shelf 10-15 km further offshore; (3) there is a large contribution of anoxic processes to total... |
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| Ano: 2011 |
URL: https://archimer.ifremer.fr/doc/00303/41423/40614.pdf |
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| Thibault De Chanvalon, A.; Metzger, E.; Mouret, A.; Knoery, Joel; Chiffoleau, Jean-francois; Brach-papa, Christophe. |
| During their transfer across estuaries, particles endure numerous cycles of deposition-resuspension accompanied by several redox oscillations. These oscillations are likely to modify the particles content of redox sensitive metals such as Fe, Mn and two rare earth elements (REE): Ce and Eu. The present paper focuses on the fate of particles originating from the Loire Estuary by the study of chemical composition changes of both total and ascorbate-extracted phases. Transformations of particles buried in the sediment are estimated from sediment cores sampled in an estuarine intertidal mudflat Changes affecting particles that are transferred to the ocean are evaluated by comparing the composition of suspended particulate matter (SPM) from riverine time series... |
| Tipo: Text |
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| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00367/47848/47935.pdf |
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| Metzger, E.; Thibault, Aubin; Cesbron, F.; Barbe, A.; Launeau, P.; Jezequel, D.; Mouret, A.. |
| The present study describes new procedures to obtain at millimeter resolution the spatial distribution of nitrite and nitrate in porewaters, combining diffusive equilibrium in thin films (DET), colorimetry and hyperspectral imagery. Nitrite distribution can be easily achieved by adapting the well-known colorimetric method from Griess (1879) and using a common flatbed scanner with a limit of detection about 1.7 µmol L-1. Nitrate distribution can be obtained after reduction into nitrite by a vanadium chloride reagent. However, the concentration of vanadium chloride used in this protocol brings coloration with a wide spectral signature that creates interference only deconvolvable by imaging treatment from an entire visible spectrum for each pixel (spectral... |
| Tipo: Text |
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| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00344/45510/45064.pdf |
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| Goineau, A.; Fontanier, C.; Jorissen, F.; Buscail, R.; Kerherve, P.; Cathalot, C.; Pruski, A. M.; Lantoine, F.; Bourgeois, S.; Metzger, E.; Legrand, E.; Rabouille, Christophe. |
| In the context of the French research project CHACCRA (Climate and Human-induced Alterations in Carbon Cycling at the River–seA connection), living (rose Bengal-stained) benthic foraminifera were investigated at two stations (24 and 67 m depth) in the Rhône prodelta (NW Mediterranean, Gulf of Lions). The aim of this study was to precise the response of benthic foraminiferal faunas to temporal changes of the Rhône River inputs (e.g. organic and terrigeneous material). Each site was sampled in April 2007, September 2007, May 2008 and December 2008, permitting to observe foraminiferal faunas of the 63–150 and >150 μm size fractions under a wide range of environmental conditions. Obvious variations in foraminiferal faunal composition were observed during... |
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| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00140/25097/23323.pdf |
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| Pastor, Lucie; Rabouille, C.; Metzger, E.; De Chanvalon, A. Thibault; Viollier, E.; Deflandre, B.. |
| Floods carry sediments to river deltas and the coastal zone, but little is known about the geochemical evolution of this particulate material deposited over a short period of time. Here, we studied two recent contrasting flood deposits in the Rhône River prodelta area (northwestern Mediterranean Sea). We monitored the porewater and solid-phase chemistry over periods ranging from a few days to 6 months after deposition. Non-steady state diagenetic processes associated with episodic deposition promote a wide spectrum of transient redox conditions in the shallow prodelta region of the Rhône. Specific attributes of diagenetic responses depend on the sources of flood material and scale (thickness) of deposition. The first flood unit of 20–30 cm was composed of... |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00449/56049/57568.pdf |
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| Thibault De Chanvalon, A.; Metzger, E.; Mouret, A.; Knoery, Joel; Geslin, E.; Meysman, F. J. R.. |
| Coastal and shelf sediments are considered as an important source of dissolved iron to the ocean. Here, we present a new numerical approach to estimate geochemical fluxes and production rates in an estuarine sediment at sub-millimetre resolution. This approach is based on application of Savitsky–Golay filter (SGF) procedure to two-dimensional concentration distributions of dissolved iron. We verified the procedure by applying it to artificial data of known production rates, and analysed the resulting uncertainty on production rates and fluxes across the water–sediment interface. This SGF procedure was applied to data from an intertidal mudflat that is densely inhabited by macrofauna (e.g. 630 ind m− 2 of Hediste diversicolor, I. Métais, pers.com.). Our... |
| Tipo: Text |
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| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00332/44365/43970.pdf |
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| De Chanvalon, A. Thibault; Metzger, E.; Mouret, A.; Cesbron, F.; Knoery, Joel; Rozuel, Emmanuelle; Launeau, P.; Nardelli, M. P.; Jorissen, F. J.; Geslin, E.. |
| We present a new rapid and accurate protocol to simultaneously sample benthic living foraminifera in two dimensions in a centimeter scale vertical grid and dissolved iron in high resolution (200 μm). Such an approach appears crucial to study foraminiferal ecology in heterogeneous environments. The foraminiferal faunas of the main intertidal mudflat of the Loire estuary are dominated by Ammonia tepida, which accounts for 92 % of the living assemblage (CTG-labeled). Its vertical distribution shows a first density maximum at the surface, a sharp decrease in the next two centimeter followed by a well defined second maximum between 3 and 8 cm depth. The heterogeneity of A. tepida in this 3–8 cm depth layer was calculated by the Moran's Index and reveals lateral... |
| Tipo: Text |
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| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00277/38786/37335.pdf |
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