HYDROGRAPHIC CHANGES OF THE SOUTHERN-OCEAN (SOUTHEAST INDIAN SECTOR) OVER THE LAST 230 KYR

Hydrographical changes of the southern Indian Ocean over the last 230 kyr, is reconstructed using a 17-m-long sediment core (MD 88 770; 46 d egrees 01'S 96 degrees 28'E, 3290m). The oxygen and carbon isotopic co mposition of planktonic (N, pachyderma sinistra and G. bulloides) and benthic (Cibicidoidies wuellerstorfi, Epistominella exigua, and Meloni s barleeanum) foraminifera have been analysed. Changes in sea surface temperatures (SST) are calculated using diatom and foraminiferal trans fer functions. A new core top calibration for the Southern Ocean allow s an extension of the method developed in the North Atlantic to estima te paleosalinities (Duplessy et al., 1991). The age scale is built usi ng accelerator mass spectrometry (AMS) C-14 dating of N. pachyderma s. for the last 35 kyr, and an astronomical age scale beyond. Changes in surface temperature and salinity clearly lead (by 3 to 7 kyr) deep wa ter variations. Thus changes in deep water circulation are not the cau se of the early response of the surface Southern Ocean to climatic cha nges. We suggest that the early warming and cooling of the Southern Oc ean result from at least two processes acting in different orbital ban ds and latitudes: (1) seasonality modulated by obliquity affects the h igh-latitude ocean surface albedo (sea ice coverage) and heat transfer to and from the atmosphere; (2) low-latitude insolation modulated by precession influences directly the atmosphere dynamic and related prec ipitation/ evaporation changes, which may significantly change heat tr ansfer to the high southern latitudes, through their control on latitu dinal distribution of the major frontal zones and on the conditions of intermediate and deep water formation.