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Abstract: The temperature influence on foraminifera growth rate was analysed using a mechanistic formulation that take into account enzyme inactivation at extreme temperatures. Growth rates are calculated using available published and unpublished laboratory culture experiments for eight species, including Neogloboquadrina pachyderma (sinistral and dextral forms), Neogloboquadrina dutertrei, Globigerina bulloides, Globigerinoides ruber, Globigerinoides sacculifer, Globigerinella siphonifera and Orbulina universa. Modeled growth formulas readily reproduce the observed growth patterns for all species. Similar growth patterns are observed for the species that have the same symbiotic algae G. ruber, G. sacculifer, and O. universa. However, different growth patterns are observed for herbivorous species (Neogloboquadrina genus) compared to carnivorous species with or without symbionts. Our growth estimates correspond well to in situ observations from both plankton tows and sediment traps. These estimates will help to improve the quantification of the effects of environmental parameters on foraminifera species distribution and abundance. [Copyright &y& Elsevier]

We closely compared high-resolution δ13C records of benthic foraminifera Cibicides wuellerstorfi, a proxy for deep-water ventilation, with the Dansgaard–Oeschger temperature oscillations. Our results reveal different perturbations of deep-water formation in the North Atlantic Ocean associated with the millennial-scale climate oscillations during the last glacial period. The cooling episodes associated with the drastic Heinrich events are related to large reductions of deep-water formation and a northward migration of 13C depleted southern source deep waters to 62°N in the North Atlantic Ocean. The inter-Heinrich events which are correlated to the other cold stadials, are marked by significant changes of sea surface temperature around the Rockall Plateau, variations in the flux of icebergs to the North Atlantic Ocean but are not associated with such important reduction of deep-water formation. If changes in the thermohaline circulation (THC) are associated with these millennial-scale climatic oscillation they affect only the deeper water masses, below 2000 m, of the North Atlantic Ocean.We thus show that equivalent degree of cooling over Greenland is obtained with different perturbations of deep-water formation. Our results either question the role of the THC as the unique explanation for these millennial-scale climate oscillations, or call upon an amplifying mechanism not yet taken into account. [Copyright &y& Elsevier]

We review the various methods which have been applied to estimate the change of seawater δ18O (δw) between the Last Glacial Maximum (LGM) and the Holocene. The most accurate constraints on these estimates are provided by the measurement of pore waters δ18O and by high resolution records of benthic foraminifer δ18O in the high latitude oceans of both hemispheres. They show that the δ18O of seawater in the deep ocean during the LGM was 1.05±0.20‰ heavier than today, with significant regional variations. Constraints resulting from ice sheet models are less accurate, because both the volume and isotopic composition of each ice sheet are still poorly known.The amplitude of the benthic δ18O change between the LGM and the Holocene, together with the δ18O and δ13C values of the benthic foraminifera genus Cibicides during the LGM, show that the Southern Ocean deep waters were extremely cold, close to the freezing point. During this time, deep waters of the South Atlantic and the Pacific oceans were at least 1.3°C warmer than those of the Southern Ocean. Overall, the glacial deep ocean, below 2500 m, was characterized by extremely cold temperatures, everywhere lower than 0°C. δ18O values of benthic foraminifer from the North Atlantic are highly variable. This variability suggests that deep Atlantic waters were not homogeneous, probably because they resulted from the sinking of different surface water masses at various locations during winter. The deep waters in the North Atlantic were at most 2°C warmer than in Southern Ocean. Alternatively, they could have been nearer the freezing point with a δ18O value lighter than the mean ocean water. Brine formation during winter would preserve such light δ18O values of the northern North Atlantic surface water. [Copyright &y& Elsevier]

Abstract: The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of the rate of the AMOC from the Last Interglaciation to the subsequent glaciation (128,000–60,000 years ago) based on sedimentary (231Pa/230Th) records. We show a deep AMOC during the interglacial warmth Marine Isotope Stage (MIS) 5.5 and a shallower glacial one during glacial MIS 4. The change between these two patterns occurred mostly during the glacial inception, i.e. the transition from MIS 5.5 to MIS 5.4. Our data show that AMOC was enhanced during this latter transition as a consequence of a large increase of the overturning rate of the Intermediate Waters, above 2500 m. We suggest that this AMOC pattern required a reinforced Gulf Stream-North Atlantic Current system that ultimately supported ice-sheet growth by providing heat and moisture to the Northern high latitudes. From MIS 5.4 to MIS 5.1, the AMOC was broadly continuous below 2000m and supported periods of ice-sheet growth. As a result, a glacial AMOC is triggered at the beginning of MIS 4 due to the extension of ice-sheet and the subsequent reorganization of deep-water formation. This study highlights the role of intermediate waters as a major player during climate change. [Copyright &y& Elsevier]

Abstract: As a part of the ANR-Forclim experiment, particle mass fluxes and sedimentation processes were investigated on the slope of Aquitanian margin of the Bay of Biscay, between the canyons of Cap-Breton and Cap-Ferret. Interface sediments were collected along a depth transect from 145 to 2000m; simultaneously a mooring line was deployed at the deepest station (WH, 2000m) with two traps (800 and 1700m) for a 16-month period (June 2006–November 2007). 210Pb activities of settling particles and of interface sediments were determined to study transport processes of particles. Sediment and mass accumulation rates, calculated from excess 210Pb profiles in the sediment column, show the expected decreasing trend with depth, as usually observed on margins. Mean particulate mass fluxes at 800 and 1700-m depth at site WH are, respectively, 27 and 70gm−2 a−1. The 210Pb budget points out events of temporary high lateral input of particles. The comparison of mass and 210Pb fluxes between the water column and the seabed indicates that lateral transport plays an important role in particle accumulation on the Aquitanian margin. Regarding the objectives of the ANR-Forclim program, which aims to improve significantly the interpretation of fossil foraminifera signals, as a proxy for hydrological changes in the North Atlantic ocean, these results highlight advection processes must be considered when interpreting fluxes of foraminifers on the Aquitanian margin. [Copyright &y& Elsevier]