Vernal sedimentation trends in north Norwegian fjords: temporary anomaly in 234Th particulate fluxes related to Phaeocystis pouchetii proliferation
(pp. 235-244, 08/03/2007)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, ICOS-RAMCES, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, NCFS, UiT, LEMAR, IRD, IFREMER, UBO EPE, CNRS
A genome-wide association study identifies novel risk loci for type 2 diabetes.
Type 2 diabetes mellitus results from the interaction of environmental factors with a combination of genetic variants, most of which were hitherto unknown. A systematic search for these variants was recently made possible by the development of high-density arrays that permit the genotyping of hundreds of thousands of polymorphisms. We tested 392,935 single-nucleotide polymorphisms in a French case-control cohort. Markers with the most significant difference in genotype frequencies between cases of type 2 diabetes and controls were fast-tracked for testing in a second cohort. This identified four loci containing variants that confer type 2 diabetes risk, in addition to confirming the known association with the TCF7L2 gene. These loci include a non-synonymous polymorphism in the zinc transporter SLC30A8, which is expressed exclusively in insulin-producing beta-cells, and two linkage disequilibrium blocks that contain genes potentially involved in beta-cell development or function (IDE-KIF11-HHEX and EXT2-ALX4). These associations explain a substantial portion of disease risk and constitute proof of principle for the genome-wide approach to the elucidation of complex genetic traits.
(Nature. vol. 445, n° 0028-0836, pp. 881-5, 22/02/2007)
GMM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ELICO, ULCO, CNRS, LOB ARCACHON, UB, INSU - CNRS, CNRS, LRCCI, UJM, CHU de Poitiers [La Milétrie], UP11, INSERM, CHSF
Evaluation of well-balanced bore-capturing schemes for 2D wetting and drying processes
(International Journal for Numerical Methods in Fluids. vol. 53, n° 0271-2091, pp. 867-894, 20/02/2007)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMB, UB, Bordeaux INP, CNRS
Evaluation of well-balanced bore-capturing schemes for 2D wetting and drying process
We consider numerical solutions of the two-dimensional non-linear shallow water equations with a bed slope source term. These equations are well-suited for the study of many geophysical phenomena, including coastal engineering where wetting and drying processes are commonly observed. To accurately describe the evolution of moving shorelines over strongly varying topography, we first investigate two well-balanced methods of Godunov-type, relying on the resolution of non-homogeneous Riemann problems. But even if these schemes were previously proved to be efficient in many simulations involving occurrences of dry zones, they fail to compute accurately moving shorelines. From this, we investigate a new model, called SURF_WB, especially designed for the simulation of wave transformations over strongly varying topography. This model relies on a recent reconstruction method for the treatment of the bed-slope source term and is able to handle strong variations of topography and to preserve the steady states at rest. In addition, the use of the recent VFRoe-ncv Riemann solver leads to a robust treatment of wetting and drying phenomena. An adapted ‘second order’ reconstruction generates accurate bore-capturing abilities.This scheme is validated against several analytical solutions, involving varying topography, time dependent moving shorelines and convergences toward steady states. This model should have an impact in the prediction of 2D moving shorelines over strongly irregular topography.
(International Journal for Numerical Methods in Fluids. vol. 53, n° 0271-2091, pp. 867-894, 20/02/2007)
MAB, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LJLL (UMR_7598), UPD7, SU, CNRS
Spartina anglica eradication experiment and in situ monitoring assess structuring strength of habitat complexity on marine macrofauna at high tidal level
The cordgrass Spartina anglica is an introduced species that tends to invade sheltered sand and mudflats, at the upper low marsh level. In Arcachon Bay, a lagoon in South West of France, the cordgrass can also replace Zostera noltii beds. The consequence of cordgrass presence on macrobenthic fauna was estimated and compared to adjacent habitats (bare sands, Z. noltii sea grass beds) during one year. The communities of the three habitats were characterised by low species richness, low abundance and biomass (when Hydrobia ulvae, 90% of abundance, is not considered) and high seasonal stability. The infaunal assemblages were particularly homogeneous between habitats without any characteristic species. Cordgrass eradication experiments were performed and zoobenthic recolonisation was observed the following year. Modifications in benthic fauna were observed on epifauna only. These results highlight the limited structuring effect of habitat heterogeneity at high tidal levels and in soft-bottom sediments where desiccation becomes the dominant factor determining infauna community structure.
(Estuarine, Coastal and Shelf Science. vol. 71, n° 0272-7714, pp. 629-640, 01/02/2007)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Present-day and past (last 25000 years) marine pollen signal off western Iberia
(Marine Micropaleontology. vol. 62, n° 0377-8398, pp. 91-114, 01/02/2007)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, ULISBOA
Importance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)
We conducted diurnal sampling in a tidal creek (Ras Dege, Tanzania) to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and biological driving forces. Since the creek has no upstream freshwater inputs, highest salinity was observed at low tide, due to evaporation effects and porewater seepage. Total suspended matter (TSM) and particulate organic carbon (POC) showed distinct maxima at periods of highest water flow, indicating that erosion of surface sediments and/or resuspension of bottom sediments were an important source of particulate material. Dissolved organic carbon (DOC), in contrast, followed the tidal variations and was highest at low tide. Stable isotope data of POC and DOC exhibit large variations in both pools, and followed tidal variations. Although the variation of d13CDOC (-23.8 to -13.8‰) was higher than that of d13CPOC (-26.2 to -20.5‰) due to the different end-member pool sizes, the d13C signatures of both pools differed only slightly at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC originated from mangrove production. At high tide, on the other hand, the DOC pool had signatures consistent with a high contribution of seagrass-derived material, whereas the POC pool was dominated by marine phytoplankton. Daily variations in CH4, and partial pressure of CO2 (pCO2) were similarly governed by tidal influence and were up to 7- and 10-fold higher at low tide, which stresses the importance of exchange of porewater and diffusive fluxes to the water column. Furthermore, this illustrates that constraining an ecosystem-level budget of these greenhouse gases in tidal systems requires a careful appraisal of tidal variations. When assuming that the high dissolved inorganic carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are due to inputs from mineralization, d13C data on DIC indicate that the source of the mineralized organic matter has a signature of -22.4‰, which shows that imported POC and DOC from the marine environment contributes strongly to overall mineralization within the mangrove system. Our data show a striking example of how biogeochemical processes in the intertidal zone appear to be prominent drivers of element concentrations and isotope signatures in the water column, and how pathways of dissolved and particulate matter exchange are fundamentally different. The estimated export of DIC through porewater exchange appears considerably larger than for DOC, suggesting that if this mechanism is indeed a major driver of solute exchange, benthic mineralization and subsequent export as DIC could represent a very significant and previously unaccounted fate of mangrove-derived C. Budgeting efforts should therefore pay attention to understanding the mechanisms and quantification of different pathways of exchange within and between both zones.
(Biogeosciences Discussions. vol. 4, n° 1810-6277, pp. 317-348, 31/01/2007)
VUB, NIOO-KNAW, ULiège, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Anomalous flow below 2700 m in the EPICA Dome C ice core detected using d18O of atmospheric oxygen measurements
While there are no indications of mixing back to 800 000 years in the EPICA Dome C ice core record, comparison with marine sediment records shows significant differences in the timing and duration of events prior to stage 11 (~430 ka, thousand of years before 1950). A relationship between the isotopic composition of atmospheric oxygen (d18O of O2, noted d18Oatm) and daily northern hemisphere summer insolation has been observed for the youngest four climate cycles. Here we use this relationship with new d18O of O2 measurements to show that anomalous flow in the bottom 500 m of the core distorts the duration of events by up to a factor of 2. By tuning d18Oatm to orbital precession we derive a corrected thinning function and present a revised age scale for the interval corresponding to Marine Isotope Stages 11–20 in the EPICA Dome C ice core. Uncertainty in the phasing of d18Oatm with respect to insolation variations in the precession band limits the accuracy of this new agescale to ±6 kyr (thousand of years). The previously reported ~30 kyr duration of interglacial stage 11 is unchanged. In contrast, the duration of stage 15.1 is reduced by a factor of 2, from 31 to 16 kyr.
(Climate of the Past Discussions [Climate of the Past Preprints]. vol. 3, n° 1814-9340, pp. 63-93, 16/01/2007)
IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, LGGE, OSUG, UJF, Grenoble INP, INSU - CNRS, IRSTEA, USMB [Université de Savoie] [Université de Chambéry], CNRS, INSU - CNRS, CNRS, NBI, UCPH, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A fourth-order compact finite volume scheme for fully nonlinear and weakly dispersive Boussinesq-type equations. Part II : boundary conditions and validation
This paper supplements the validation of the fourth-order compact finite volume Boussinesq-type model presented by Cienfuegos et al. We discuss several issues related to the application of the model for realistic wave propagation problems where boundary conditions and uneven bathymetries must be considered. We implement a moving shoreline boundary condition following the lines given by Lynett et al., while an absorbing-generating seaward boundary and an impermeable vertical wall boundary are approximated using a characteristic decomposition of the Serre equations. Using several benchmark tests, both numerical and experimental, we show that the new finite volume model is able to correctly describe nonlinear wave processes from shallow waters and up to wavelengths which correspond to the theoretical deep water limit. The results compare favourably with those reported using former fully nonlinear and weakly dispersive Boussinesq-type solvers even when time integration is conducted with Courant numbers greater than 1.0. Furthermore, excellent nonlinear performance is observed when numerical computations are compared with several experimental tests on solitary waves shoaling over planar beaches up to breaking. A preliminary test including the wave-breaking parameterization described by Cienfuegos (Fifth International Symposium on Ocean Wave Measurement Analysis, Madrid, Spain, 2005) shows that the Boussinesq model can be extended to deal with surf zone waves. Finally, practical aspects related to the application of a high-order implicit filter as given by Gaitonde et al. to damp out unphysical wavelengths, and the numerical robustness of the finite volume scheme are also discussed.
(International Journal for Numerical Methods in Fluids. vol. 53, n° 0271-2091, pp. 1423-1455, 09/04/2026)
LEGI, UJF, Grenoble INP, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
H4 abrupt event and late Neanderthal presence in Iberia
Heinrich event 4 (H4) is well documented in the North Atlantic Ocean and the adjacent continents as a cooling event 39,000 yr before present (BP). To quantify the impact of this event with respect to climate and vegetation over the Iberian Peninsula, we perform numerical experiments using a high-resolution general circulation model forced by sea surface temperatures before and during H4. Our model simulates an expansion of aridity over the peninsula during H4, a desertification of the south, and a replacement of arboreal by herbaceous plants in the north, all of which are in agreement with contemporaneous pollen sequences from marine cores located off the Iberian Peninsula. Our simulations demonstrate that the H4 marine event imprinted drastic changes over Southern Iberia, which would not have favoured its occupation by Anatomically Modern Humans, therefore providing a plausible explanation for the delayed extinction of Neanderthals in this region inferred from the archaeological record.
(Earth and Planetary Science Letters. vol. 258, n° 0012-821X, pp. 283 à 292, 09/04/2026)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, ArScAn, UP1, UP8, UPN, MCC, CNRS, LGGE, OSUG, UJF, Grenoble INP, INSU - CNRS, IRSTEA, USMB [Université de Savoie] [Université de Chambéry], CNRS, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PACEA, UB, CNRS, GW