Current map and bathymetry from p band sar images : preliminary results
Microwave remote sensing at very long wavelength is already used and validated for coastal zone regions and regions covered by ice (Antarctica) using airborne systems. For many other applications, a high potential exists and the PYLA 2001 experiment allowed the acquisition of data for fields still under preliminary tests. The experiment was carried on a Transall aircraft (French army/DGA) and used the SAR sensor RAMSES (multifrequency/multipolarization) from ONERA by P. Paillou et al. (2001). For the experiment, the acquisition was performed in P band (435 MHz). The aim was to explore potentials of the low frequency domain for sub-surface moisture detection (Pyla sand dune), biomass evaluation (Nezer forest), mapping of the ocean bathymetry and salinity (Arcachon inlet, estuary of the river Gironde), and archaeology (St Germain d'Esteuil, Dignac, Moulin du Fa). A dedicated P-band calibration site was set up in order to fully exploit the polarimetric information. This part of the study consists of analyzing SAR images from RAMSES (P band) in order to be able to take into account the effect of longer surface waves, winds and currents on the surface roughness in the Arcachon inlet. Tidal currents associated with long oceanic waves recorded at the mouth of the inlet, including the northern channel and sand banks of the ebb tidal delta. The analysis provides tools allowing the production of current maps, which are in turn compared to in-situ measurements by GPS on surface drifting buoys and to current velocity fields provided by a 2DH numerical model, MARS-2D. The evaluation of the ability of a 1D hydrodynamical model applied to SAR images in order to reproduce currents in the area presented. Multipolarization images can be used in order to separate the information associated with the ocean surface (tilt) modulation, which is different for each polarimetric image, from the hydrodynamic modulation, similar for each image. The tilt modulation is representative of a Real Aperture Radar-like (RAR) image. The data being available quite late, we just performed correlations between each set of data by using polarimetric coefficient. We obtain good answers on the information associated with the motion of the scatterers.
(. vol. 2, pp. 960-962, 23/10/2026)
TAMCIC, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER
Bias in the paleoceanographic time series: Tests with a numerical model of U, C org , and Al burial
(Paleoceanography. vol. 17, n° 0883-8305, pp. 6-1-6-11, 01/09/2002)
CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRS, CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE
Terrigenous fluxes at the Celtic margin during the last glacial cycle
(Marine Geology. vol. 188, n° 0025-3227, pp. 79-108, 01/08/2002)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Geomagnetic-assisted stratigraphy and sea surface temperature changes in core MD94-103 (Southern Indian Ocean): possible implications for North-South climatic relationships around H4
New records of past sea surface temperatures (SSTs) were derived in the 30-50 kyr B.P. time interval from a core located at 45° S in the Southern Indian Ocean, MD94-103. To investigate the climatic phasing between the Southern Indian Ocean, the Greenland and the Antarctic ice, the magnetic signal of core MD94-103 was synchronized at better than millennial accuracy in the vicinity of the Laschamp geomagnetic to a reference record, NAPIS-75, already placed on the GISP2 age model. Coccolithophorid and diatom species abundances both point to a cooling of surface waters during H4. Specific diatoms also indicate lower salinity waters during the same time interval. These observations do not support the idea that the South hemisphere warmed 1.5-2 kyr before the North hemisphere (Nature 394 (1998) 739). Rather, alkenone-derived SSTs suggest that cold conditions have characterized the surface waters in the south latitudes during H4 and H5, and that temperature at evaporation sites contributed to the isotopic events A1 and A2 visible in the isotopic records of central Antarctica (Earth Planet. Sci. Lett. 177 (2000) 219). SSTs obtained from foraminifera assemblages depict somewhat different temperature patterns, possibly indicative of water stratification.
(Earth and Planetary Science Letters. vol. 201, n° 0012-821X, pp. 159-170, 01/07/2002)
CLIMAG, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Experimental Study of Interactions between Purple and Green Sulfur Bacteria in Sandy Sediments Exposed to Illumination Deprived of Near-Infrared Wavelengths
(Applied and Environmental Microbiology. vol. 68, n° 0099-2240, pp. 2972-2981, 01/06/2002)
MCAM, MNHN, CNRS, ECOLAG, UM2, IFREMER, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Differential δ13C and δ15N signatures among scallop tissues: Implications for ecology and physiology
There have been several studies where the isotopic composition of organisms has been determined seasonally, but fewer have examined separate organs. In this context, separate organs (e.g. gonad, digestive gland and muscle), of a suspension-feeder, the scallop Pecten maximus, were used to assess seasonal changes of both stable isotopes and biochemical components. Our study used multiple indicators (stable carbon and nitrogen isotopes ratios, biochemical components and seston Chl a) to track nutritive activity and energy allocation in P. maximus from the Bay of Brest (France). In addition to seasonal variation in the isotopic composition of P. maximus tissues, we found strong differences in the mean isotopic signatures of different organs. This has serious implications for interpretation of animal diets and potential use in animal physiology. Furthermore, we present evidence that seasonal variations of metabolism will cause changes in the isotopic composition not related to changes in the diet. Interpretation of isotopic data may require consideration of values from several separate organs. Finally, 15N appears powerful to track metabolite fates in the scallop P. maximus.
(Journal of Experimental Marine Biology and Ecology. vol. 275, n° 0022-0981, pp. 47– 61, 24/05/2002)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, VUB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A systemic approach to mercury biomagnification in rivers affected by goldmining activities (French Guiana)
(01/05/2002)
UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR MALY, IRSTEA, LMBA, UBS, UBO EPE, CNRS
Mercury contamination of freshwater systems in French Guiana : a statistical approach of risk assessment
(01/05/2002)
LMBA, UBS, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UB
Direct numerical simulation of turbulence–mean field interactions in a stably stratified fluid
Freely decaying turbulent flows in a stably stratified fluid are simulated with a pseudo-spectral numerical code solving the fully nonlinear Navier–Stokes equations under the Boussinesq approximation with periodic boundary conditions. The flow is decomposed into a turbulent field and a horizontal mean flow ū ( z , t ) defined as the average of the horizontal velocity component in a horizontal plane at height z and time t . Similarly, the density field is decomposed into a turbulent field and a (stable) mean density profile ρ ( z , t ) defined as the average of the density field in a horizontal plane at height z and time t . Attention is paid to the effect of the turbulent velocity field on an initial z -periodic horizontal mean flow (Simulation A) or an initial z -periodic perturbation of the mean density profile (Simulation B). Both A and B are performed under conditions of moderate and strong stratification and are compared to the non-stratified simulations. Simulation A shows that the turbulence–mean flow interaction is strongly affected by the buoyancy forces. In the absence of a stratification, the mean flow perturbation decays rapidly due to the turbulent diffusion of momentum. When a moderate stratification is applied, the mean flow perturbation decays much more slowly whereas it oscillates and grows with time when the stratification is strong. These results are interpreted by defining a time-dependent eddy viscosity. Whereas the eddy viscosity coefficient has positive values in the non-stratified simulation, it is affected by the buoyancy forces and decreases after a period of order N −1 . For large times, the eddy diffusivity oscillates and its time-averaged value over a few turnover timescales is positive but small when the stratification is moderate, and roughly zero when the stratification is strong. These results are interpreted by defining a time-dependent eddy viscosity. Whereas the eddy viscosity coefficient has positive values in the non-stratified simulation, it is affected by the buoyancy forces and decreases after a period of order N −1 in the stratified simulations (where N is the Brunt–Väisälä frequency associated with the background linear stratification). At large time, we find that the eddy viscosity remains roughly zero when the stratification is moderate, whereas it oscillates but remains persistently negative in the strongly stratified case, which causes the horizontal mean flow to accelerate. We conclude that the presence of a stable stratification strongly affects the temporal behaviour of the mean quantities ū and ρ in turbulent flows and partly explains the formation of horizontal layers in stratified geofluids such as oceans and atmospheres.
(Journal of Fluid Mechanics. vol. 455, n° 0022-1120, pp. 213-242, 15/04/2002)
IMFT, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, CERFACS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats
In the meso-oligotrophic Bay of Biscay, a diminishing downward organic matter flux with depth is accompanied by an important decrease of the live foraminiferal density. Although bottom water oxygenation is not directly influenced by organic matter input, the oxygenation of interstitial waters and the primary redox fronts do change in response to variations of the organic matter flux. The occurrence of deep and intermediate infaunal taxa can be linked to fundamental redox fronts and putative associated bacterial consortia. Our data are in agreement with the TROX-model, which explains the benthic foraminiferal microhabitat as a function of organic flux and benthic ecosystem oxygenation. Both the depth of the principle redox fronts and the microhabitat of deep infaunal species show important increases with depth. At the deepest oligotrophic stations, deep infaunal faunas become relatively poor. Therefore, the exported flux of organic matter appears to be the main parameter controlling the composition and the vertical distribution of benthic foraminiferal faunas below the sediment-water interface. The oxygenation of pore waters plays only a minor role. A species-level adaptation of the TROX-model is presented for the Bay of Biscay.
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 49, n° 0967-0637, pp. 751-785, 01/04/2002)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS