Entity

Time filter

Source Type


Retailleau S.,University of Angers | Retailleau S.,CNRS Nantes Laboratory of Planetology and Geodynamics | Schiebel R.,University of Angers | Howa H.,University of Angers | Howa H.,Laboratory of Marine Bio Indicators LEBIM
Marine Micropaleontology | Year: 2011

Population dynamics of planktic foraminifer species are discussed in relation to environmental factors across the continental slope onto the shelf of the southeastern Bay of Biscay. Along a bathymetric transect from 2000. m to 145. m water depth, 154 vertical plankton tows were obtained during different seasons on five cruises between June 2006 and July 2008. The distribution of live specimens (> 100 μm) sampled at distinct intervals down to 700. m water depth is compared to changes in temperature, salinity, and chlorophyll-aconcentration. The overall seasonal variability and depth distribution of species in the hemipelagic southeastern Bay of Biscay has been similar to open ocean faunas in the pelagic North Atlantic. Each species examined occurred at considerable variability in habitat depth and seasonal distribution. The vertical distribution of planktic foraminifer species was mainly driven by the depth of the Deep Chlorophyll Maximum (DCM) and hence linked to the development of the thermocline. The seasonal variation of river discharge could have had differential effects on the distribution of planktic foraminifers, and may have inhibited or triggered the production of species. Low standing stocks at onshore stations in spring, and high standing stocks in July both in low saline waters indicate that salinity in itself did not control the distribution of planktic foraminifers. Instead, factors which co-vary with salinity, such as turbidity and organic matter possibly affected the distribution of planktic foraminifers on a species-specific scale. In general, the distribution of planktic foraminifer species on a seasonal, vertical, and regional scale along the offshore-onshore transect was related to surface water salinity and turbidity, and to the availability of food. © 2011 Elsevier B.V. Source


Pina-Ochoa E.,University of Aarhus | Koho K.A.,University Utrecht | Geslin E.,University of Angers | Geslin E.,Laboratory of Marine Bio Indicators LEBIM | Risgaard-Petersen N.,University of Aarhus
Marine Ecology Progress Series | Year: 2010

In a laboratory experiment, we examined the prolonged survival and behaviour of the benthic foraminiferan Globobulimina turgida under 3 simulated natural conditions: oxygenated with added nitrate, anoxic with added nitrate, and anoxic. The survival rates, adenosine triphosphate (ATP) reserve and intracellular nitrate pool of G. turgida were measured periodically under these conditions. Furthermore, to evaluate the efficiency and energy yield of the respiration system, denitrification rates of individual specimens were quantified using the acetylene inhibition and N2O microsensor technique at the start of the experiment. Our results demonstrate that the long-term (56 d) survival rate (64 %) and ATP concentrations of G. turgida were not significantly different in oxygenated and anoxic, nitrate-containing conditions (Mann-Whitney test, p > 0.05). Thus, G. turgida can survive prolonged anoxia (3 mo) as long as nitrate is available to sustain its respiration. However, it remains unsure whether growth or reproduction can take place under anoxia. Short-term (21 to 35 d) survival rates were lower in nitrate-free, anoxic conditions (22% recovered alive compared to 62 to 82% in nitrate-oxic or nitrate-anoxic conditions), but foraminifera were observed to survive up to 56 d if respiring from their intra-cellular nitrate pool only. The foraminiferal nitrate pool appears very dynamic, as wide ranges of concentrations were measured in living specimens (0 to 463 mM ind. -1). We postulate that the scatter in the nitrate pool measurements highlights the ability of the foraminifera to actively collect and respire on nitrate, depending on individuals' history of exposure to oxygen and nitrate. © Inter-Research 2010. Source


Schumacher S.,University of Angers | Schumacher S.,Laboratory of Marine Bio Indicators LEBIM | Jorissen F.J.,University of Angers | Jorissen F.J.,Laboratory of Marine Bio Indicators LEBIM | And 3 more authors.
Marine Micropaleontology | Year: 2010

We determined the stable oxygen and carbon isotopic composition of live (Rose Bengal stained) tests belonging to different size classes of two benthic foraminiferal species from the Pakistan continental margin. Samples were taken at two sites, with water depths of about 135 and 275m, corresponding to the upper boundary and upper part of the core region of the oxygen minimum zone (OMZ). For Uvigerina ex gr. Uvigerina semiornata and Bolivina aff. Bolivina dilatata, δ13C and δ18O values increased significantly with increasing test size. In the case of Uvigerina ex gr. U. semiornata, δ13C increased linearly by about 0.105‰ for each 100-μm increment in test size, whereas δ18O increased by 0.02 to 0.06‰ per 100 and mum increment. For Bolivina aff. B. dilatata the relationship between test size and stable isotopic composition is better described by logarithmic equations. A strong positive linear correlation is observed between δ18O and δ13C values of both taxa, with a constant ratio of δ18O and δ13C values close to 2:1. This suggests that the strong ontogenetic effect is mainly caused by kinetic isotope fractionation during CO2 uptake. Our data underline the necessity to base longer δ18O and δ13C isotope records derived from benthic foraminifera on size windows of 100μm or less. This is already common practice in down-core isotopic studies of planktonic foraminifera. © 2010 Elsevier B.V. Source


Griveaud C.,University of Angers | Griveaud C.,Laboratory of Marine Bio Indicators LEBIM | Jorissen F.,University of Angers | Jorissen F.,Laboratory of Marine Bio Indicators LEBIM | Anschutz P.,Bordeaux University
Micropaleontology | Year: 2010

We investigated benthic foraminiferal densities, composition, and microhabitats at three sampling stations on the Portuguese margin, at 980, 1860and 3125m water depth. For each site, we studied two sets of three replicate cores, sampled during two successive multi-corer deployments. Our resultsshow an overall trend of decreasing foraminiferal densities from the shallowest to the deepest site, in response to a decreasing labile organic matterflux to the sea floor. Faunas at 980m are strongly dominated by Uvigerina mediterranea, which shows a conspicuous faunal density maximum close to the sediment surface. At 1860m, the surface faunas are much poorer, and no longer dominated by a single taxon. Cibicidoides robertsonianus, C. kullenbergi, Uvigerina peregrina, Gavelinopsis translucens and Hoeglundina elegans arepresent in about equal quantities. The deep infaunal community at these twostations is dominated by Globobulimina affinis, and has comparable densities. At 3125m, the faunas are very poor in 5 of the 6 cores, and mainly consist of agglutinant taxa. At all three stations, important differences are observed between the 6 studied cores. At 980m, the faunal density is about 4 times higher in one of the cores, mainly due to high numbers of Uvigerina mediterranea. This could be explained by the position of this core in a topographical depression, where organic matter concentrates. At 1860m, two setsof three cores, taken during two successive multicorer deployments, containdifferent amounts of deep infaunal taxa. Finally, at 3125m, one of the 6 cores contains an exceptionally rich deep infaunal community (up to 450 individuals per 50cm), dominated by the calcareous taxa Fursenkoina bradyi, Globobulimina affinis and Chilostomella oolina. The fact that the subrecent fossil faunas of three studied cores from this site are all enriched in these taxa indicates that the observed high infaunal standing stocks are a recurrent phenomenon, in response to a currently unidentified process that strongly concentrates metabolisable organic matter in deeper sediment layers. Source


Barras C.,University of Angers | Barras C.,Laboratory of Marine Bio Indicators LEBIM | Barras C.,French Climate and Environment Sciences Laboratory | Duplessy J.-C.,French Climate and Environment Sciences Laboratory | And 5 more authors.
Biogeosciences | Year: 2010

The geochemical composition of deep-sea benthic foraminiferal calcite is widely used to reconstruct sea floor paleoenvironments. The calibration of the applied proxy methods has until now been based on field observations in complex natural ecosystems where multiple factors are interfering. However, laboratory experiments with stable physico-chemical conditions appear to be the ideal way to evaluate the influence of a single parameter. In this paper, we present the oxygen isotopic composition of deep-sea benthic foraminiferal shells entirely calcified under controlled experimental conditions over a large temperature range (4 to 19 °C). The new laboratory protocols developed for this study allowed us to produce large quantities of shells in stable conditions, so that also the shell size effect could be investigated. It appears that when considering a narrow test size range, the curve describing the temperature dependency of δ 18O in Bulimina marginata is parallel to the thermodynamically determined curve observed in inorganically precipitated calcite (.0.22‰ °C -1). This observation validates the use of δ 18O of this benthic species in paleoceanographical studies. Over the studied size range (50 to 300 μm), the effect of test size was 0.0014‰ μm -1, confirming previous suggestions of a substantial test size effect on δ 18O of benthic foraminifera. This study opens new perspectives for future proxy calibrations in laboratory set-ups with deep-sea benthic foraminifera (e.g. quantification of the influence of the carbonate chemistry). © 2010 Author(s). Source

Discover hidden collaborations