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 changes during the last glacial maximum: the North Atlantic Deep Water (NADW) was shallower than today and the Antarctic Bottom Water (AABW) penetrated much farther north(1-6). Numerical ocean models have, so far, been unable to simulate these circulation changes realistically(7). Here we show that a zonally averaged, three-basin ocean model, driven by 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 during glacial times. Our results suggest that the glacial production of AABW was slightly higher than at present, whereas that of NADW was reduced by similar to 40%, resulting in an intermediate circulation cell which closed within the Atlantic basin. We also show that the strength of the Atlantic conveyor belt strongly depends on the surface density contrast between the high latitudes of the Northern and Southern hemispheres.