Hydrological Cycle Scenarios, Deep Ocean Circulation, and Century/Millennium Climate Change: A Simulation Study Using an Ocean-Atmosphere-Ice Sheet Model

Abstract

Rapid climate changes (Dansgaard-Oeschger events) during most of the last glaciation and during the last deglaciation, seen in the Greenland ice cores and a deep sea sediment core in the North Atlantic, are likely caused by dynamical instability of the climate system itself. Here we present, with a simple coupled ocean-atmosphere-ice sheet energy-salt balance model (ESBM), oscillatory feedback mechanisms to explain these climate changes. The major physical mechanisms active in the model are latitudinal heat and salt transports by the thermohaline circulation in the North Atlantic, surface ocean freshwater fluxes associated with melting and growing continental ice sheets in the Northern Hemisphere and with Atlantic to Pacific water vapor transport. The primary positive feedback is between the production of North Atlantic Deep Water (NADW) and the meridional salinity flux to the high latitude North Atlantic Ocean. The principal negative feedback is between the freshwater flux either to or from the continental ice sheets and meridional heat flux to the high-latitude North Atlantic accomplished by the thermohaline circulation.