Fluvial transport of suspended sediment and organic carbon during flood events in a large agricultural catchment in southwest France.
Water draining from a large agricultural catchment of 1 110 km2 in southwest France was sampled over an 18-month period to determine the temporal variability in suspended sediment (SS) and dissolved (DOC) and particulate organic carbon (POC) transport during flood events, with quantification of fluxes and controlling factors, and to analyze the relationships between discharge and SS, DOC and POC. A total of 15 flood events were analyzed, providing extensive data on SS, POC and DOC during floods. There was high variability in SS, POC and DOC transport during different seasonal floods, with SS varying by event from 513 to 41 750 t; POC from 12 to 748 t and DOC from 9 to 218 t. Overall, 76 and 62% of total fluxes of POC and DOC occurred within 22% of the study period. POC and DOC export from the Save catchment amounted to 3090 t and 1240 t, equivalent to 1·8 t km−2 y−1 and 0·7 t km−2 y−1, respectively. Statistical analyses showed that total precipitation, flood discharge and total water yield were the major factors controlling SS, POC and DOC transport from the catchment. The relationships between SS, POC and DOC and discharge over temporal flood events resulted in different hysteresis patterns, which were used to deduce dissolved and particulate origins. In both clockwise and anticlockwise hysteresis, POC mainly followed the same patterns as discharge and SS. The DOC-discharge relationship was mainly characterized by alternating clockwise and anticlockwise hysteresis due to dilution effects of water originating from different sources in the whole catchment.
(Hydrological Processes. vol. 25, n° 0885-6087, pp. 2365-2378, 15/07/2011)
LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
New Arabian Sea records help decipher orbital timing of Indo-Asian monsoon
A recent study suggested that Indian monsoonal proxies commonly used in the Arabian Sea, in general productivity proxies, could be impacted by changes in the Atlantic overturning rate (AMOC) throughout a control on the nutrient delivery into the euphotic zone. This oceanic mechanism could lead to a misunderstanding between the Indian summer monsoon (SM) and orbital forcing and could confuse a direct comparison with other archives derived from other monsoonal sub-systems (such as East-Asian or African records). Here we analyze three independent proxies (bromine, foraminifera assemblages and grain size) extracted from a marine sediment core (MD04-2861) covering the last 310 ka, and retrieved in the northern Arabian Sea near the Makran margin, an area influenced by summer and winter Indian monsoon. The grain size proxy deals with the regional continental climate through fluvial and eolian processes. It cannot be linked to changes in nutrient content of AMOC and present the same phase relationship (timing) than the other SM proxies. This demonstrates that the productivity signals (Bromine) in the northern Arabian Sea are mainly controlled by SM dynamics and not AMOC modulated nutrients at orbital scale changes. We thus build a multi-proxy record of SM variability (i.e. SM stack) using statistical tools (principal component analysis) further compiled on an age model constructed independently from orbital tuning. We find that strong SM lag by 9 ± 1 ka the NH summer insolation maximum (minimum of precession, June 21 perihelion and obliquity maximum) in the precession band, and by 6 ± 1.3 ka in the Obliquity band. These results are consistent with previous studies based on marine and terrestrial records in both Indian and Asian regions, except Asian speleothems. Our study supports the hypothesis that internal climate forcing (decreased ice volume together with the increase of latent heat export from the southern Indian Ocean) set the timing of strong Indo-Asian summer monsoons within both the precession and obliquity cycle. The external forcing (direct sensible heating) initiate monsoonal circulation. Strong Indian winter monsoon (WM) occurs between ice maxima and northern hemisphere sensible heat minima, indicating that both act to strengthen WM circulation. The summer and winter monsoons are in antiphase in the precession band suggesting that the two systems are dynamically linked.
(Earth and Planetary Science Letters. vol. 308, n° 0012-821X, pp. 433 - 444, 13/07/2011)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Recent advances in Serre-Green Naghdi modelling for wave transformation, breaking and runup processes
To describe the strongly nonlinear dynamics of waves propagating in the final stages of shoaling and in the surf and swash zones, fully nonlinear models are required. The ability of the Serre or Green Naghdi (S-GN) equations to reproduce this nonlinear processes is reviewed. Two high-order methods for solving S-GN equations, based on Finite Volume approaches, are presented. The first one is based on a quasi-conservative form of the S-GN equations, and the second on a hybrid Finite Volume/Finite Difference method. We show the ability of these two approaches to accurately simulate nonlinear shoaling, breaking and runup processes.
(European Journal of Mechanics - B/Fluids, n° 0997-7546, pp. doi:10.1016/j.euromechflu.2011.02.005, 06/07/2011)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGI, UJF, Grenoble INP, CNRS, IMT, UT Capitole, Comue de Toulouse, INSA Toulouse, INSA, Comue de Toulouse, UT2J, Comue de Toulouse, UT3, Comue de Toulouse, CNRS, PUC, DMA, ENS-PSL, PSL, CNRS, I3M, UM2, UM, CNRS
Relationship between valve activity, microalgae concentration in the water and toxin accumulation in the digestive gland of the Pacific oyster Crassostrea gigas exposed to Alexandrium minutum.
The complexity of the relationships between Alexandrium minutum (A.m.) concentration in the water ([A.m.]w), Paralytic Shellfish Poisoning contamination in the digestive gland ([PSP]dg) and valve behavior was explored in oysters Crassostrea gigas. Two experiments were conducted, during which oysters' valve behaviour were analyzed. Oysters, first acclimated for 10-days with the non harmful microalgae Heterocapsa triquetra (H.t.) were exposed to 4 microalgae mixtures at constant total concentrations of 10∙103 cells.ml-1 (experiment-1) and 5∙103 cells.ml-1 (experiment-2): 100% A.m.; 50% A.m.-50% H.t.; 25% A.m.-75% H.t.; 100% H.t. At the end of experiment-2, [PSP]dg were measured. At 10∙103 cells.ml-1, the microalgal ingestion decreased (p < 0.05) with increasing [A.m.]w but not at 5∙103 cells.ml-1 (p > 0.05). The frequency of microclosures specifically increased with [A.m.]w (p < 0.05) and the opening duration with [PSP]dg (p < 0.0001). Oysters exhibiting the maximum increase in opening duration also exhibited the highest [PSP]dg. The results are discussed in terms of oyster physiology and origin of the behavioral response.
(Marine Pollution Bulletin. vol. 62, n° 0025-326X, pp. 1191-1197, 01/07/2011)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, UEB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PHYC, DYNECO, IFREMER
Modeling rip current circulations and vorticity in a high-energy mesotidal-macrotidal environment
In June 2007 an intense 5 day field experiment was carried out at the mesotidal-macrotidal wave-dominated Biscarrosse Beach on a well-developed bar and rip morphology. Previous analysis of the field data elucidated the main characteristics of a tide-modulated and strongly evolving rip current driven by low- to high-energy shore-normal waves. Here we present a modeling strategy based on the vertically integrated and time-averaged momentum equations accounting for roller contribution that is applied to the Biscarrosse experiment. Wave and flow predictions in the surf zone improve significantly when using a spatially constant time-varying breaking parameter by Smith and Kraus (1990). The model correctly reproduces the main evolving behaviors of the rip current. An advection-diffusion equation governing the mean wave-driven current vertical vorticity is further derived from the momentum equations. Vertical vorticity is driven by a forcing term that depends on the breaking wave energy dissipation and on the wave propagation direction. Spatial gradients in depth-induced broken-wave energy dissipation therefore determine both the strength and the sign of the wave-driven circulation rotational nature. When applied to the Biscarrosse experiment, the vorticity efficiently predicts the main characteristics of the evolving rip current such as its width, cross-shore extension, and intensity. In addition, good correlations are found between the maximum rip current intensity and the deviation of the forcing term. Thus, we determine precisely the rotational component associated with the wave forcing which is less direct through the traditional radiation stress approach.
(Journal of Geophysical Research. Oceans. vol. 116, n° 2169-9275, pp. C07026, 01/07/2011)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM
HYPXIM: A new hyperspectral sensor combining science/defence applications
This paper synthesizes the technical requirements made by a group of French scientists and defence users expert in hyperspectral imagery to design a new space borne imaging spectrometer. This project called HYPXIM is currently in phase 0 mission study and two French aerospace companies have proposed solutions that are analysed by the CNES. These technical requirements are converted into at-sensor radiance specifications for each scientific application and the final radiance set used for the instrument design is defined.
(pp. 1-4, 06/06/2011)
LDG, DAM/DIF, DAM, CEA, LPGN, UN, CNRS, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité, BRGM, DGA, CNES, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Spatial and temporal variations in trace metal concentrations in surface sediments of the Marennes Oléron Bay. Relation to hydrodynamic forcing
Sediments quality assessment is of priority concern to provide a comprehensible overview of ecological and chemical state of an ecosystem. The Marennes-Olé ron Bay, hosting the largest oyster production in France, is influenced by the historic polymetallic pollution of the Gironde Estuary. Despite, management efforts and decreasing emissions in the Gironde watershed, Cd levels in oysters from the bay are close to consumption limit (5 mg g À 1 dw, EC no. 466/2001). In this context, the aim of the study was to assess the priority metal (Ni, Cu, Zn, As, Ag, Cd, Hg, Pb and Th) concentrations in sediment within the Bay, by investigating spatial and temporal distribution variations and the role of hydrodynamic forcing. For that we selected three sites (east, west and south) characterizing different environments of the Bay and we observed metal concentrations, grain size distribution, bed elevation and wave activities during a year survey. The sampling strategy pointed out both spatial and temporal metal concentrations variability in sediment. In general, metal enrichments were close to geochemical background. The eastern part of the Bay, largely influenced by the Charente river particulate deposition, presented constant concentrations over the survey. In contrast, in the western part, bed elevation was strongly influenced by hydrodynamic forcing especially wave activities, and metal distribution showed constant metal concentrations except very located Cd minor enrichment related to the Gironde influence via the Antioche Strait (north). The southern part was disconnected from the rest of the Bay and showed minor to very located moderately severe Cd enrichment, related to the Gironde water discharges via the Maumusson Strait (south). Thus, the multidisciplinary approach was relevant to characterize the interactions between hydrodynamic forcing on the environment and sediments and their metal quality state which (i) were close to geochemical background over a year for Ni, Cu, Zn, As, Ag, Hg and Pb (i) which presented enrichment of Cd in the western and southern part.
(Continental Shelf Research. vol. 31, n° 0278-4343, pp. 997-1007, 01/06/2011)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER
Sediment delivery and depositional patterns off Adélie Land (East Antarctica) in relation to late Quaternary climatic cycles
This study focuses on the understanding of depositional patterns over late Quaternary glacial/interglacial cycles and of the influence of diagenesis on geochemical sedimentary records from the continental margin off Adélie Land (East Antarctica). We provide a complete analysis of the 30-m-long sediment core MD03-2603, collected on a deep-sea sediment mound deposit. The LR04 benthic oxygen isotope stack vs. down-core records of Ba/Al and Ba/Ti atomic ratios, reflectance data and micropaleontological evidence, allow to determine a detailed chronology back to ~ 490 ka BP. Long-lived Uranium and Thorium (238 U, 234 U, 232 Th, and 230 Th) provide an assessment of lateral vs. vertical sediment advection, by constraining the sediment focusing factor (Φ). Φ is high in most glacial intervals, when mostly detrital material was transported down-slope and focused to the core area. Interglacials display highs in Ba/Al and Ba/Ti, coupled to low Φ values, related to stronger contour current flow. Biogenic fractions are more abundant during interglacials and more diluted by detrital fractions during glacials. The diatom assemblage is dominated by the open-ocean species Fragilariopsis kerguelensis, but glacial intervals display an increase of sea-ice related and coastal species. The integrated approach (high-resolution record of major and minor elements, U auth , δ 15 N, N org , δ 13 C, and C org) provides key insights into how redox conditions affect glacial/interglacial sedimentation processes. Our evidence shows that diagenetic effects, due to development of reducing conditions and consequent higher preservation of organic matter, may overprint the paleoclimatic significance of some proxies involved into a sequence of diagenetic remineralization pathways. Comparison of the marine record to ice-core data (EPICA Dome C-EDC) allows to extend the information to the whole East Antarctic margin. Sediment proxies of increased burial of biogenic material, or increased preservation of organic matter, are linked to climatic amelioration on the continent. Highs in EDC dust flux correlate with high Mn/Al and Mo/Al ratios within the sediment record, confirming that establishment of colder conditions on the continent triggered changes in sedimentation rates at the glacial/interglacial transition, which in turn affected the development of reducing redox fronts within the sediment.
(Marine Geology. vol. 284, n° 0025-3227, pp. 96-113, 01/06/2011)
LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, UP1, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Influence of the organic matter composition on benthic oxygen demand in the Rhône River prodelta (NW Mediterranean Sea)
(Continental Shelf Research. vol. 31, n° 0278-4343, pp. 1008-1019, 01/06/2011)
EDF R&D STEP, EDF R&D, EDF [E.D.F.], EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, BIAF, UA, OCEANIS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LOBB, OOB, UPMC, CNRS, UPMC, INSU - CNRS, CNRS, LGCgE, UA, LECOB, SU, CNRS, OOB, SU, CNRS, CRIOBE, UPVD, EPHE, PSL, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS
Roles of regional hydrodynamic and trophic contamination in cadmium bioaccumulation by Pacific oysters in the Marennes-Oléron Bay (France)
The Marennes-Oléron Bay, hosting the largest oyster production in France, is influenced by the historic polymetallic pollution of the Gironde Estuary. Despite management efforts and decreasing emissions in the Gironde watershed, cadmium levels in oysters from the bay are close to the consumption limit (5 lg g À1 dw, EC). From mid April to mid July 2009, we investigated the role of tidal resuspension and regional hydrodynamics on Cd speciation (seawater, SPM, phytoplankton, sediment, microphytobenthos) and bioaccumulation in 18 month-old oysters (gills, digestive glands, rests of tissues) reared under natural conditions (i) at $60 cm above the sediment and (ii) on the sediment surface. Dissolved and particulate Cd concentrations in surface and bottom waters were similar and constant over tidal cycle suggesting the absence of Cd release during sediment resuspension. Temporal dissolved and particulate Cd concentrations were closely related to Gironde Estuary water discharges, showing increasing concentrations during flood situations and decreasing concentrations afterwards. Cd depletion in the water column was associated with increasing Cd in the [20-100 lm] plankton fraction, suggesting Cd bioaccumulation. After 3 months, enrichment factors of Cd in tissues of oysters exposed in the water column and directly on the sediment were respectively 3.0 and 2.2 in gills, 4.7 and 3.2 in digestive glands and 4.9 and 3.4 in remaining tissues. Increasing Cd bioaccumulation in gills, digestive glands and remaining tissues can be related to elevated dissolved Cd in the bay, suggesting gill contamination via the direct pathway and subsequent internal redistribution of Cd to other organs and tissues. Elevated Cd contents in oysters reared on tables could be attributed to different trophic Cd transfer (phytoplankton versus micro-phytobenthos) or to different oyster metabolisms between the rearing conditions as suggested by metal-lothionein concentrations.
(Chemosphere. vol. 84, n° 0045-6535, pp. 80-90, 01/06/2011)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LERPC, COAST, IFREMER