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
Influence of the parasite worm Polydora sp. on the behaviour of the oyster Crassostrea gigas: a study of the respiratory impact and associated oxidative stress
The aim of this study was to investigate how the worm Polydora sp., which induces oysters into creating mud blisters in response to an irritation within their shells, could interfere with the oyster Crassostrea gigas physiology and ethology. The impact was characterized by studying two groups of oysters (non-parasitized and parasitized) during a 30 days period: (1) the animal behaviour by analysing their valve activity (valvometry), and (2) the animal respiratory physiology by measuring in vivo the oxygen partial pressure and the specific oxygen consumption in selected tissues (heart, fast and slow adductor muscle). We also researched a putative impact on the expression of several oxidative stress genes at the heart level. Our results show that Polydora sp. is clearly an oyster’s parasite as it induces a decrease in oyster growth according to the infestation intensity. Moreover, it modifies the behaviour and the respiratory physiology of the molluscs. Infested animals opened more frequently but for less time and their level of blood oxygenation was systematically higher than healthy molluscs. These high levels of oxygenation had no effect on the oxidative metabolism of the tissues studied but they induced oxidative stress. Indeed, the superoxide dismutase gene showed a threefold increase in expression in the heart of infested oysters. A putative scenario of the weakening mechanism is proposed.
(Marine Biology. vol. 152, n° 0025-3162, pp. 329-338, 22/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Holocene long- and short-term climate changes off Adélie Land, East Antarctica
Diatom data from a marine sediment core give insight on Holocene changes in sea‐surface conditions and climate at high southern latitudes off Adélie Land, East Antarctica. The early to mid‐Holocene was warmer than the late Holocene with a transition at ∼4000 calendar years B. P. Sea ice was less present and spring‐summer growing season was greater during the warm period relative to the cold one, thus limiting sea ice diatom production and favoring more open ocean diatom to develop. The long‐term Holocene climatic evolution in East Antarctica is explained by a combination of a delayed response to local seasonal insolation changes coupled to the long memory of the Southern Ocean. Abrupt variations of the diatom relative abundances, indicating rapid climate changes, are superimposed to the Holocene long‐term trends. Spectral analyses calculate robust frequencies at ∼1600 a (where “a” is years), ∼1250 a, ∼1050 a, ∼570 a, ∼310 a, ∼230 a, ∼150–125 a, ∼110 a, ∼90 a, and ∼66 a. Such periods are very close to solar activity cyclicities, except for the periods at ∼310 a and ∼1250 a, which are close to internal climate variability cyclicities. Wavelet analyses estimate the same periods but indicate nonstationary cyclicities. Rapid climate changes at high southern latitudes may therefore be explained by a combination of external (solar) and internal (thermohaline circulation) forcings.
(Geochemistry, Geophysics, Geosystems. vol. 8, pp. n/a-n/a, 22/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, PROMES, UPVD, CNRS
Climate variability of the last five isotopic interglacials: Direct land-sea-ice correlation from the multiproxy analysis of North-Western Iberian margin deep-sea cores
(pp. 375-386 (chapter 25), 22/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Gas transfer velocities of CO2 and CH4 in a tropical reservoir and its river downstream
We have measured simultaneously the methane (CH4) and carbon dioxide (CO2) surface concentrations and water–air fluxes by floating chambers (FC) in the Petit-Saut Reservoir (French Guiana) and its tidal river (Sinnamary River) downstream of the dam, during the two field experiments in wet (May 2003) and dry season (December 2003). The eddy covariance (EC) technique was also used for CO2 fluxes on the lake. The comparison of fluxes obtained by FC and EC showed little discrepancies mainly due to differences in measurements durations which resulted in different average wind speeds. When comparing the gas transfer velocity (k600) for a given wind speed, both methods gave similar results. On the lake and excluding rainy events, we obtained an exponential relationship between k600 and U10, with a significant intercept at 1.7 cm h− 1, probably due to thermal effects. Gas transfer velocity was also positively related to rainfall rates reaching 26.5 cm h−1 for a rainfall rate of 36 mm h− 1. During a 24-h experiment in dry season, rainfall accounted for as much as 25% of the k600. In the river downstream of the dam, k600 values were 3 to 4 times higher than on the lake, and followed a linear relationship with U10.
(Journal of Marine Systems. vol. 66, n° 0924-7963, pp. 161-172, 22/02/2026)
LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, CNRM, INSU - CNRS, CNRS, Comue de Toulouse, IREQ
Tidal modulation of wave-setup and wave-induced currents on the Aboré coral reef
As waves break on a reef, they create a radiation stress gradient that drives wave-setup and wave-induced currents. In this paper, tidally modulated wave-induced current and wave-setup are presented and analysed from field measurements performed on the Aboré coral reef in the southwest lagoon of New Caledonia. We show, in agreement with analytical models by Symonds et al (1995) and Hearn (1999), that this tidally modulated wave circulation is mainly controlled by the difference between the depth at the breakpoint and the water depth over the reef. A specific calibration of these models is proposed for the Aboré reef.
(Journal of Coastal Research. vol. Special Issue 50, n° 0749-0208, pp. 762 - 766 ICS2007, 22/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRD [Nouvelle-Calédonie], ECOLA, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS