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
Consistency in diatom response to metal-contaminated environments
Diatoms play a key role in the functioning of streams, and their sensitivity to many environmental factors has led to the development of numerous diatom-based indices used in water quality assessment. Although diatom-based monitoring of metal contamination is not currently included in water quality monitoring programs, the effects of metals on diatom communities have been studied in many polluted watersheds as well as in laboratory experiments, underlying their high potential for metal contamination assessment. Here, we built large database of river diatoms (comprising more than 600 taxa) that were exposed to various loads of heavy metals in the water was investigated. The samples were collected during field surveys carried out in 6 different countries (France, Spain, Switzerland, Canada, Vietnam, China). After taxonomy harmonization, the patterns in diatom community structure were investigated for 202 samples, all collected from hard substrates in rivers with circumneutral water pH. As the sites were contaminated by a mixture of different metals (mainly Al, As, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Zn) with various loads, metal concentrations were converted into a single score after Clements et al. (2000) in order to classify sites according to potential metal toxicity. Metal contamination proved to be a strong driver of the community structure, and enabled for the identification of tolerant species like Eolimna minima, Surirella angusta, Cocconeis placentula var. euglypta or Pinnularia parvulissima. Traits were also tested: diatom cell size and the occurrence of diatom deformities were found to be good indicators of high metal contamination. This work provides a basis for further use of diatoms as indicators of metal pollution Clements WH, Carlisle DM, Lazorchak JM, Johnson PC, 2000. Heavy metals structure benthic communities in Colorado mountain streams.
(pp. 1, 15/05/2011)
UR REBX, CEMAGREF, IRSTEA, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSTEA, ICRA, UdG, UdG, GEPV, CNRS
Development of q-PCR approaches to assess water quality: Effects of direct cadmium exposure on gene expression of the diatom Eolimna minima
In regard to the degradation of water quality since the last decades, appropriate diagnostic tools have been implemented. In France, water agencies in collaboration with Cemagref have developed a diatom index to estimate global water quality. The Biological Diatom Index (BDI, Coste et al. 2009) is routinely used for monitoring applications in European territories and has been standardized (NF T 90-354). Nevertheless, indices currently used for water quality assessment don't take in consideration metal contamination in their conception, despite the high bioaccumulation and impact shown on periphytic diatom communities (da Silva et al., 2009, Cunningham et al., 2005, Feurtet-Mazel et al., 2003). Moreover these methods are time consuming and require important taxonomic knowledge. In this context development of q-PCR approaches are of particular interest. In our study we have developed a new RNA extraction method for diatoms, 8 genes of interest for the diatom Eolimna minima have been selected, sequenced and deposited in the GenBank. The responses of the q-PCR tools developed have been tested after Cd exposure on Eolimna minima. Bioaccumulation and population kinetics were also followed.
(pp. 1, 15/05/2011)
UR REBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sensitivity of beach morphodynamics to climate variability. Application to truc vert beach (France)
Coastal systems should be vulnerable to climate change/variability. The present paper investigates the sensitivity of Truc Vert beach to present day climate conditions as well as possible climate change in the near future. A modeling approach is used, based on three numerical morphodynamic models (MORPHODYN, MARSOUIN, TELEMAC). The first results show an important sensitivity to present day wave classes. Some first indications on the potential influence of wave climate changes are also given, investigating variations of wave classes characteristics. The present work also illustrates the need to go on improving and developing these models.
(06/05/2011)
BRGM, UR OHAX, CEMAGREF, LMA, AMU, ECM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGI, UJF, Grenoble INP, CNRS
Marine diatoms in polar and sub-polar environments and their application to Late Pleistocene paleoclimate reconstruction
(IOP Conference Series: Earth and Environmental Science. vol. 14, n° 1755-1307, pp. 012006, 01/05/2011)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS