Bottom water production variability in the Ross Sea slope during the Late Pleistocene-Holocene as revealed by Benthic Foraminifera and sediment geochemistry

The Antarctic area produces bottom waters that ventilate the vast majority of the deep basins in the rest of the world ocean. The rate of formation in the source area and the strength of these cold bottom waters are key factors affecting the Global Thermohaline Circulation during modern and past climate conditions. We present the results of a multidisciplinary study carried out on a sediment core collected on the slope off the Drygalski Basin (Ross Sea) for the Late Pleistocene-Holocene. The results obtained allow the following main observations: 1) two main intervals (15-10 and 7.5-6 cal kyr BP) mark subsequent enhanced nutrient supply because of a higher efficiency in the Upper CDWupwelling; 2) within this general context, an oscillatory trend is present from 15 kyr BP to present time, indicated by the measured parameters. A possible hypothesis to interpret these oscillations is that foraminifers concentration minima, corresponding to minima in %OC and to reversal of 14C (relative increase of older carbon) and to colder (atmospheric) condition, reflect dilution in the sediment because of rapid accumulation of fine sediment re-suspended at the shelf edge by the cascading currents. The minima may represent higher rate of bottom water formation; 3) the detected oscillations (minima) seem to correlate to colder conditions in Adelie Land record where increased sea-ice cover and bottom water formation were suggested.