Bathymétrie littorale par télédétection : méthodes, précision et finalités
Cet article fait le point sur les principales techniques d'inversion bathymétrique en zone littorale par télédétection. Ces techniques exploitent différents types de capteurs (lidar, photographie numérique, vidéo) sur des plateformes atellitaires, aéroportées ou fixes. Les mesures bathymétriques obtenues se distinguent par leur résolution spatiotemporelle, l'emprise spatiale des zones couvertes et leur précision. Ces techniques ont récemment été expérimentées sur des plages sableuses très dynamiques, évoluant rapidement sous l'action des vagues et des courants, ce qui permet d'évaluer leur pertinence vis-à-vis des échelles des différents processus d'intérêt en dynamique sédimentaire littorale. La précision des reconstructions bathymétriques est très variable allant de 0,1 à 0,95 m. Outre le choix de la plateforme d'observation qui détermine les échelles spatiales couvertes et la résolution planimétrique, ce sont les contraintes de mise en oeuvre (météo, coût financier) et la maturité des méthodes qui conditionnent la précision de la mesure réalisée et leur positionnement vis-à-vis de la temporalité des processus et des évolutions morphologiques observés
(pp. 457-468, 01/06/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM, LDO, INSU - CNRS, UBO EPE, CNRS
Long term and recent climate changes recorded in North Atlantic oceanic archives around iceland
This contribution will compile paleoceanographic and paleoclimatic works which, over the last decades, provided major insights in our understanding of the Earth's climate natural variability and the underlying forcing mechanisms. A focus will be made on peri-icelandic marine records which document the climatic pace at different time-scales and are supported by multiproxy evidences. A special attention to the link in between the ocean and the cryosphere will be done.
(11/05/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The holocene climatic history of the Circum-icelandic oceanic realms
One of the achievements of the IPY was to foster an unprecedented amount of research initiatives aiming at studying recent (Holocene) changes in ocean circulation and climate in the subarctic and arctic domains. Paleo-investigations offer invaluable information on natural environmental changes at decadal to millennial scale, as well as on the processes driving them. We hereby present some recent results based on proxy records from circum Icelandic areas.
(11/05/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Short-term metallothionein inductions in the edible cockle Cerastoderma edule after cadmium or mercury exposure: Discrepancy between mRNA and protein responses
Metallothioneins (MT) are essential metal binding proteins involved in metal homeostasis and detoxification in living organisms. Numerous studies have focused on MT response to metal exposure and showed an important variability according to species, metal, concentration and time of exposure. In this study, the expression of one isoform of MT gene (Cemt1) and associated MT protein synthesis were determined after 1, 3, 9, 24, 72 and 168h of cadmium (Cd) or mercury (Hg) exposures in gills of the cockle Cerastoderma edule. This experiment, carried out in laboratory conditions, revealed that in Cd-exposed cockles, induction of Cemt1 is time-dependent following a "pulse-scheme" with significant upregulation at 24h and 168h intersected by time point (72h) with significant downregulation. MT protein concentration increases with time in gills of exposed cockles in relation with the progressive accumulation of Cd in soluble fraction. On contrary, Hg exposure does not lead to any induction of Cemt1 mRNA expression or MT protein synthesis compared to control, despite a higher accumulation of this metal in gills of cockles compared to Cd. The localization of Hg (85-90%) is in insoluble fraction, whereas MT was located in the cytoplasm of cells. This gives us a first clue to understand the inability of Hg to activate MT synthesis. However, other biochemical processes probably occur in gills of C. edule since the remaining soluble fraction of Hg exceeds MT sequestration ability. Finally, since one of the first main targets of metal toxicity in cells was the mitochondria, some genes involved in mitochondria metabolism were also analyzed in order to assess potential differences in cellular damages between two metal exposures. Indeed, until T(168), no impact on mitochondrial genes was shown following Hg exposure, despite the complete lack of MT response. This result indicated the presence of other effective cellular ligands which sequester the cytosolic fraction of this metal and consequently inhibit metal reactivity. Such competition mechanisms with other cytosolic ligands more sensitive to Hg were particularly argued in the discussion.
(Aquatic Toxicology. vol. 97, n° 0166-445X, pp. 260-267, 01/05/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Biomarker responses in polar cod (Boreogadus saida) exposed to the water soluble fraction of crude oil
In order to mimic the biological effects of an oil spill in Arctic waters, we examined several types of biomarkers (genes, enzymes, metabolites, and DNA damage) in polar cod Boreogadus saida experimentally exposed to the water soluble fractions of crude oil. During 4 weeks of exposure, induction of the studied biomarkers exceeded baseline levels. The mRNA expression of the cytochrome P4501A1 (cyp1a1) gene was the most promising biomarker, with glutathione S-transferase (gst) as a suitable complement. The delayed ethoxyresorufin O-deethylase (EROD) and GST activities and their persistence following 2 weeks of depuration may allow detection of previous exposures in field samples. The composition of PAH metabolites in the bile indicated the bioavailability of different PAH size-classes. Although mRNA expressions of antioxidant defense genes were induced at start of the exposure, with the strongest responses from catalase and cytosolic superoxide dismutase, they were poor for oil monitoring purposes due to their very short response times. Significant DNA damage demonstrated genotoxicity even at low PAH concentrations (<15 μg L−1) and was correlated with benzo(a)pyrene and pyrene metabolites in the bile.
(Aquatic Toxicology. vol. 97, n° 0166-445X, pp. 234-242, 01/05/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Millennial-scale variability in Atlantic water advection to the Nordic Seas derived from Holocene coccolith concentration records
Abundance patterns of coccolith species in two Holocene marine cores retrieved off Norway and northern Iceland are indicative of millennial-scale modulations in the flow of the main (Norwegian Atlantic Current) and secondary (North Iceland Irminger Current) branches of the North Atlantic Drift to the Nordic Seas. Long-term trends in coccolith abundance changes reflect major Holocene steps in Atlantic Water transfer to the Nordic Seas at orbital scale with important constraints on the convective activity of the Nordic Seas that leads to the formation of the precursor water mass of North Atlantic Deep Water. Millennial-scale Holocene episodes of increased advection of Atlantic waters off Norway are associated with enhanced winter precipitation over Scandinavia, increased sea-salt fluxes over Greenland, and strengthened wind over Iceland, thereby suggesting a common atmospheric forcing: the location and intensity of the westerlies and the associated changes in mid-to high-latitude pressure gradients. Our biotic data indicate an opposite pattern of Atlantic water inflow at suborbital scale between the western (Denmark) and eastern (IcelandeScotland) straits of the northern Atlantic throughout the Holocene. This, as supported by present observational and simulated data, further highlights the role of atmospheric oscillations in the recent history of the North Atlantic-Nordic Seas water mass exchanges across the GreenlandeScotland Ridge. Such atmospheric processes are thought to explain the observed coupling between periods of excess export of arctic sea-ice to the Nordic Seas and intervals of maximum inflow of Atlantic water to the Norwegian Sea throughout the last 11 000 years.
(Quaternary Science Reviews. vol. 29, n° 0277-3791, pp. 1276 - 1287, 01/05/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Temporal Dynamics of River Biofilm in Constant Flows
A 15-week experiment was performed in a riverside laboratory flume (with diverted river water) to check variations of river biofilm structure (biomass, algal and bacterial compositions) and function (community gross primary production GPP and respiration) under constant flow while water quality went through natural temporal variations. One major suspended matter pulse coinciding with one river flood was recorded after 10 weeks of experiment. Epilithic biofilm first exhibited a 10-week typical pattern of biomass accrual reaching 33 g ash-free dry matter (AFDM) m–2 and 487 mg chlorophyll-a m–2 and then, experienced a shift to dominance of loss processes (loss of 60% AFDM and 80% chlorophyll-a) coinciding with the main suspended matter pulse. Algal diversity remained low and constant during the experiment: Fragilaria capucina and Encyonema minutum always contribute over 80% of cell counts. DGGE banding patterns discriminated between two groups that corresponded to samples before and after biomass loss, indicating major changes in the bacterial community composition. GPP/R remained high during the experiment, suggesting that photoautotrophic metabolism prevailed and detachment was not autogenic (i.e., due to algal senescence or driven by heterotrophic processes within the biofilm). Observational results suggested that silt deposition into the biofilm matrix could have triggered biomass loss.
(International Review of Hydrobiology. vol. 95, n° 1434-2944, pp. 156-170, 01/05/2010)
LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, UPV / EHU, IMFT, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Population dynamics and secondary production of the cockle Cerastoderma edule: A comparison between Merja Zerga (Moroccan Atlantic Coast) and Arcachon Bay (French Atlantic Coast)
Cockle (Cerastoderma edule) population dynamics were studied at the southern limit of the distribution of this marine bivalve in Merja Zerga, Morocco. Parameters such as growth, mortality, and production were compared with those of a population at Arcachon Bay (France) a site in the center of the cockle's range. At each sampling period between two and three cohorts were simultaneously observed at each site and the average total abundance was usually higher at Merja Zerga. Recruitment occurred at both sites in spring when temperature rose above 19 °C, independently of the month. In Merja Zerga, winter recruitment was also observed at one occasion, following high sediment disturbance. The first year (2005–06) at Merja Zerga, the mortality rate was close to nil for juveniles and was Z = 1.5 yr− 1 for adults, providing a high production (64 g dry weight m− 2 yr− 1). At Arcachon during the same period, the juvenile mortality rate was Z = 10.9 yr− 1, the adult mortality rate was 3.4 yr− 1 and production was 26 gDW m−2 yr− 1. The second year (2006–07), mortality after recruitment was much higher (Z = 8.6 yr− 1, for juveniles) and similar to what was observed at Arcachon (Z = 8.4 yr− 1). Mortality rate of adults was higher at Merja Zerga (Z = 3.0 yr− 1) than at Arcachon (Z = 1.5 yr− 1). Production was lower at Arcachon than at Merja Zerga although growth performances were higher at Arcachon. The higher growth performance at Arcachon (Φ′ = 3.3) was mainly due to high asymptotic length (L∞ = 38 mm) and was related to low intraspecific competition compared to Merja Zerga where cockle abundance was higher (Φ′ = 3.1, L∞ = 31 mm). P/B was low in both sites and slightly higher at Arcachon (1.1–1.5 against 1.0–1.1 yr− 1). At Arcachon, recruitment was correlated with temperature, a peak occurring when temperature rose above 19 °C (June–July). At Merja Zerga, recruitment was already 2–3 months earlier but was not significantly correlated to temperature. This study showed that population dynamics of cockles at the southern limit of this distribution fell in the range of what was observed elsewhere in the North-Eastern Atlantic coast. Most factors that were involved in population regulation (intraspecific competition, predation and sediment dynamics) were not strictly dependent on latitude. The direct role of temperature (latitude dependent factor) was not obvious. Variation in temperature could explain the recruitment delay between Arcachon and Merja Zerga and the low maximum shell length at Merja Zerga.
(Journal of Sea Research (JSR). vol. 63, n° 1385-1101, pp. 191-201, 01/04/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Oxygen and organic carbon fluxes in sediments of the Bay of Biscay
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 57, n° 0967-0637, pp. 528-540, 01/04/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Cadmium-induced genotoxicity in zebrafish at environmentally relevant dose
(Ecotoxicology and Environmental Safety. vol. 73, n° 0147-6513, pp. 312-319, 01/03/2010)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LMBA, UBS, UBO EPE, CNRS