Résolution numérique en volumes finis d'un système d'équations de Serre étendu
Un schéma de résolution numérique en volumes finis pour un système d’équations de Serre étendu est présenté. En utilisant des solutions analytiques tests nous montrons que celui-ci fournit une erreur de discrétisation globale de $\{O[(\Delta x)^4],O[(\Delta t)^4]\}$. Le traitement numérique des conditions aux limites de trait de côte mobile et d’absorption-génération d’ondes au large doit permettre d’aborder l’étude de la propagation de la houle sur une plage. La comparaison des résultats numériques avec des mesures expérimentales de propagation d’ondes solitaires sur une plage confirme la capacité des équations de Serre à reproduire les non-linéarités associées au raidissement des ondes dans la zone de levée et l’amplitude limite de celles-ci.
(pp. 383-390, 21/02/2026)
LEGI, UJF, Grenoble INP, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Elemental compositions, FT-IR spectral and thermal behavior of sedimentary fulvic and humic acids from aquatic and terrestrial environments
Studies on elemental analysis, Fourier transform infrared spectroscopy (FT-IR) and thermal decomposition (thermogravimetry, TG; and derivative thermogravimetry, DTG) of sedimentary fulvic (FA) and humic acids (HA) from marine, estuarine, lacustrine and terrestrial environments are presented. In general, H/C and N/C atomic ratios, as well as the infrared spectra, reflected the extent of the influence of algal and/or terrestrial organic matter sources on the samples, the aquatic (both, marine and freshwater) humic substances (HS) being richer in nitrogen and more saturated, than terrestrial materials. Comparison of properties of FA and HA from the same parent sediments showed that the latter are relatively richer in nitrogen and unsubstituted aliphatic chains and poorer in carboxylic groups. FT-IR spectra showed that the nitrogen present is mostly as forming part of amide groups. Concerning thermal degradation, two main steps were observed for all samples: the first, relative to the loss of moisture, being located between 40°C and 100°C and the second between 270°C and 440°C. FT-IR spectra of the samples which had been heated to 90°C, 400°C and 900°C showed that, upon heating, the carboxyl content decreases (especially for FA), the aliphaticity decreases and the aromaticity increases (especially for HA), indicating that the 270°C-470°C degradation step might be related to decarboxylation and unsaturation losses. In spite of this, both kinds of HS, were shown to be highly thermo-resistant materials retaining most of their typical original infrared spectral features, even after being heated to 400°C. \textcopyright 2004 by The Geochemical Society of Japan.
(Geochemical Journal. vol. 38, pp. 255--264, 21/02/2026)
UCS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Organic matter accumulation and preservation controls in a deep sea modern environment: an example from Namibian slope sediments.
The Lüderitz upwelling cell is presently the most productive area of the Benguela current system and abundant organic matter (OM) accumulates on the adjacent slope sediments even at great water depth. OM from two cores taken on the slope and covering the last 280 kyear was analysed in terms of "petroleum quality" (Rock-Eval), chemical features (FTIR, EDS) and petrographic composition (light microscopy and TEM). These data indicate that the OM is more oxidized at 3606 m water depth than on the upper slope sediments (1029 m) although the petroleum quality of the OM throughout the deep-water core remains surprisingly high for hemipelagic deep-sea sediments (HI=200–400 mg/g). The petroleum quality of OM accumulated on the upper slope is consistently high: HI averages 450 mg/g. Two petrographic types of OM are distinguishable from microscopic observation, each ascribed to distinctive preservation mechanisms: (1) ‘Granular' amorphous OM, which dominates in the deep-water core, is formed by organo-mineral aggregates. Aggregation appears to be the primary preservation mode at this depth although is quantitatively limited (maximum TOC value of 4 wt.% of bulk sediment obtained through this process). The ultrastructure of the aggregates highlights an intimate association pattern between sedimentary OM and clays. (2) ‘Gel-like' nannoscopically amorphous OM (NAOM) largely dominates at 1000 m water depth and contains sulfur. Thus, early diagenetic sulfurization was probably involved in the preservation of this OM, but a contribution from the classical degradation–recondensation pathway cannot be ruled out. Moreover, selective preservation occurred at both sites but represents an insignificant part of the OM. Organic fluxes mainly control the occurrence and extent of sulfurisation at both water depths by determining the redox conditions at the sea floor. Aggregate formation is limited by both organic and mineral fluxes at the lower slope whereas OM supply is never limiting on the upper slope. Although consistently operating through time at both depths, preservation by organo-mineral association is limited by mineral availability and thus accounts for a relatively minor portion of the OM accumulated on this organic-rich slope. In the case of large organic fluxes, sulfurisation and/or degradation–recondensation is required to obtain TOC contents above 4 wt.% of bulk sediment in the area.
(Organic Geochemistry. vol. 35, n° 0146-6380, pp. 5, 543-559, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ISTO, INSU - CNRS, UO, CNRS
A Garden of Eden for Gibraltar Neandertals ? A reply to Finlayson et al.
Reflections on the possible role of climate in cultural change and human population replacement are still rare. In this respect, the comments provided by Finlayson and collaborators to our paper must be welcomed and considered as a valuable opportunity to go deeper into the mechanisms of such interactions. However, we find a number of contradictions and inconsistencies in the way in which they deal with the issue of Neandertal extinction, with minimal data to support their conclusions, and consider that in a number of instances they have inaccurately reported our views.
(Quaternary Science Reviews. vol. 23, n° 0277-3791, pp. 1210-1216, 21/02/2026)
PACEA, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Relationship between Antarctic sea ice and southwest African climate during the late Quaternary
Here we compare late Quaternary southwest African climate records from the west coast of southern Africa (published winter rainfall and trade wind intensity records from a core off the coast of Namibia) to records of Antarctic sea-ice extent. This comparison reveals coherent changes between Antarctic sea-ice extent and the southwest African winter rain region since 45 k.y. B.P., with enhanced winter rainfall and trade-wind vigor during periods of increased sea-ice presence. We propose an oceanic and atmospheric coupling between Antarctic sea ice and the winter rainfall zone of southwest Africa that may lead to increased desertification in the region if global warming persists.
(Geology. vol. 32, n° 0091-7613, pp. 909, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CAU
Cockle Cerastoderma edule population mortality: Role of the digenean parasite Himasthla quissentensis
Infection patterns of the digenean trematode Himasthla quissetensis in its second intermediate host, the edible cockle Cerastoderma edule, and the impact of this parasite on cockle populations were quantified. A 2 yr transplant experiment and a 4 yr survey were conducted in Arcachon Bay, a coastal lagoon on the Atlantic SW coast of France. Cockles free of H. quissetensis were transplanted at La Canelette, a station where cockles were usually highly infected. Infection began in May, when the water temperature reached 17degreesC and stopped in November (12degreesC). There was no new infection between November and April. Monthly surveys at 2 stations, Arguin and La Canelette, confirmed that cockle infection by H. quissetensis occurred during the warmer period of the year. Only cockles with a shell length > 8 mm became infected; therefore, cockle growth rate, which differed at the 2 stations, was also a key factor explaining infection phenology. In winter, the mean parasite abundance of H quissetensis in cockles decreased at both stations. The mortality rate of parasites in cockles was very low, with no seasonal pattern, and did not explain this winter decrease. Consequently, the decrease of H. quissetensis was interpreted as mortality of heavily infected cockles. At Arguin, where the cockle population was characterised by moderate abundance, high growth rate and short lifespan, cockle mortality amounted to 93% during the first year of benthic life, with no significant contribution of parasites; in the following year (Year 2), cockle mortality was 85%, with 28% due to H. quissetensis infection. At La Canelette, the cockle population, characterised by low abundance and low growth rate, suffered almost 100% mortality in the first year, with no contribution by parasites, which started to infect cockles in the second year only; the remaining cockles had a long lifespan (up to 5 yr), and > 46% of their mortality was linked to H. quissetensis infection. It is concluded that both host growth rate and water temperature are important factors in the initiation of parasite infection and that the intensity of infection and its effect on host mortality closely depend on host growth and environmental factors.
(Marine Ecology Progress Series. vol. 279, n° 0171-8630, pp. 141-150, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effects of digenean trematodes and heterotrophic bacteria on mortality and burying capability of the common cockle Cerastoderma edule (L.)
Population dynamics of marine invertebrates is controlled by a variety of abiotic and biotic factors. Among these, some have received lesser attention from marine ecologists because of their ‘discrete’ nature. This is the case of parasitism and bacterial load. In the present study, we focused on the role that both digenean trematodes and heterotrophic aerobic bacteria might play in the mortality and burying behaviour of cockles, Cerastoderma edule. The bivalves were sampled monthly during 1 year from two sites in Arcachon Bay (French Atlantic coast). Mortality rates were assessed after transferring in the laboratory normally buried and unburied (i.e. found lying at the sediment surface at low tide) cockles. Their digenean and bacterial loads were determined for both positions (normally buried and unburied). Mortality rate was significantly higher for cockles found out of the sediment at low tide, suggesting that this abnormal position was a prelude to cockles' death. Comparison of digenean load of cockles showed no significant difference between buried and unburied bivalves. In contrast, bacterial load was significantly higher in unburied cockles than in normally buried animals. The effect of high concentration of a marine bacterial strain (Pseudomonas fluorescens) on cockles' burying behaviour and mortality was tested in the laboratory. Results showed that these bacteria could trigger the emergence of animals from the sediment but did not cause cockles' death. These field observations and laboratory experiments suggest that bacteria, rather than digenean trematodes, could play a role in the emergence of cockles and, hence, affect their survival in the wild.
(Journal of Experimental Marine Biology and Ecology. vol. 293, n° 0022-0981, pp. 89-105, 26/08/2003)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The Gulf of Cadiz: An unstable giant contouritic levee
Recent multibeam bathymetry and acoustic imagery data provide a new understanding of the sedimentary system located in the Gulf of Cadiz which is under the influence of a strong current, the Mediterranean Outflow Water (MOW). When it comes out from the Strait of Gibraltar, the MOW is either channelled along major or secondary channels, or spills over a sedimentary levee. Frequent earthquakes and the constant current shearing generate widespread sediment deformation and instability of contourite deposits. Secondary channels can form by retrogression following an initial failure. At their mouth, sediment accumulates in the form of small sandy contourite lobes. These observations suggest that the Gulf of Cadiz system shares many similarities with channel-levee complexes formed by turbidity current activity. The main difference is that, in the Gulf of Cadiz, the main process is a strongly flowing saline current which locally interacts with gravity processes.
(Geo-Marine Letters. vol. 23, n° 0276-0460, pp. 7-18, 01/08/2003)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Secondary settlement of cockles Cerastoderma edule as a function of current velocity and substratum: a flume study with benthic juveniles
Some newly-settled bivalve molluscs can experience a second dispersal stage in the water column and colonize areas distant from initial settlement zone ('secondary settlement'). To document mechanisms involved in such a process, experiments were conducted in a recirculating 13-m flume, using juvenile cockles Cerastoderma edule (shell length between 0.8 and 5.7 mm). After 4 h and under current surface velocities of 10, 20 and 24 cm s−1, all juveniles left the plexiglass substratum (site of initial introduction) and 42.4, 58.6 and 76.2% of juveniles, respectively, were retrieved from a downstream sand area (which only represented 7.7% of the total flume surface). Naked-eye observations showed that smaller individuals were borne within the water column, whereas larger individuals tended to roll or slip on the substratum. Byssus threads produced by the juveniles were often seen, sometimes covered in sand grains. These observations were confirmed by finding larger juveniles in the upstream part of the sand area. When sand was replaced by mud, a reduced proportion of cockles was retrieved in the experimental substratum (18.4, 20.0 and 16.4%, respectively). Observations showed that juveniles rarely succeeded in anchoring themselves in mud. When initially introduced on a favourable substratum (medium sand), more than 87% of juveniles were retrieved from that sand array at all flow velocities. This study shows that secondary settlement occurs for juvenile cockles up to 5.7 mm in shell length and depends not only on flow velocity but on substratum type.
(Hydrobiologia. vol. 503, n° 0018-8158, pp. 103 - 116, 01/08/2003)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
A decarbonation and preservation method for the analysis of organic C and N contents and stable isotope ratios of low-carbonated suspended particulate material
The aim of this study was to determine a simple routine procedure to preserve, decarbonate and analyse low-carbonated filters of suspended particulate organic matter (POM) for particulate organic carbon and nitrogen content, δ13C and δ15N. Our goal was to analyse these four parameters from a single and entire filter of POM without altering the organic material. First, freezing (-20°C) versus oven-drying (60°C) were compared as the initial preservation step. Afterwards, non-acidified samples were compared to acid-treated samples using 0.12N HCl (diluted HCl rinsing at the end of the filtration) or 12N HCl (filters exposed to HCl fumes for four hours in a dessicator). Regarding the preservation methods, our results indicate that freezing increases the uncertainty of δ15N measurements and, in combination with concentrated HCl treatment, leads to a loss of particulate nitrogen and an alteration of the δ15N signature. Consequently, we recommend drying to preserve filter samples. Regarding acid treatments, we found that (i) diluted HCl would not be sufficient to fully remove the carbonate from our samples, (ii) in contrast, a four-hour exposure of the filters to the HCl fumes was enough to remove all the inorganic carbon, and (iii) the concentrated HCl treatment did not alter the nitrogen measurements (only when drying without freezing is used to preserve the filters). Consequently, we propose that low-carbonated POM filters are preserved by drying and carbonates are removed by exposing the filters to HCl fumes (four hours) for the analysis of particulate organic C and N content and isotope ratios.
(Analytica Chimica Acta. vol. 491, n° 0003-2670, pp. 125–133, 27/06/2003)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, IRD, VUB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRS, UBO IFCS, UBO EPE, CHU - BREST, IUEM, IRD, INSU - CNRS, UBO EPE, CNRS, LAIEM, UN UFR ST, UN, CNRS