Global ocean circulation and its past variations.

Quantitative reconstruction of past sea water temperature, salinity and ventilation from marine sediment has provided an original approach to reconstruct the global ocean circulation and its past variations. These reconstructions may be compared to simulations performed either by forcing a 2-D or 3-C Ocean Circulation Model by sea surface temperature, salinity and wind stress or by forcing a fully coupled climate model (atmosphere-ocean-sea ice) by past boundary conditions such as those of the last glacial maximum (insulation, ice sheets, continental albedo and vegetation). This paper describes the main results that have been obtained over the last twenty years and discusses remaining uncertainties. Palaeoceanogaphic reconstructions have shown that the global ocean circulation was deeply different from that of today during the last glaciation and that major changes may develop in less than a few centuries. Comparable changes may occur in response to the human induced climate change of the next centuries. (C) 2004 Academie des sciences. Publie par Elsevier SAS. Tous droits reserves.