A MODEL STUDY OF THE ATLANTIC THERMOHALINE CIRCULATION DURING THE LAST GLACIAL MAXIMUM

STABLE isotope measurements in deep-sea sediment cores have indicated that the Atlantic thermohaline circulation experienced significant cha nges during the last glacial maximum: the North Atlantic Deep Water (N ADW) was shallower than today and the Antarctic Bottom Water (AABW) pe netrated much farther north(1-6). Numerical ocean models have, so far, been unable to simulate these circulation changes realistically(7). H ere we show that a zonally averaged, three-basin ocean model, driven b y glacial boundary conditions(8-10), reproduces the main trends of the geochemically constrained glacial Atlantic circulation. In addition, we provide quantitative estimates of the meridional water transport du ring glacial times. Our results suggest that the glacial production of AABW was slightly higher than at present, whereas that of NADW was re duced by similar to 40%, resulting in an intermediate circulation cell which closed within the Atlantic basin. We also show that the strengt h of the Atlantic conveyor belt strongly depends on the surface densit y contrast between the high latitudes of the Northern and Southern hem ispheres.