RAPID INTERGLACIAL CLIMATE FLUCTUATIONS DRIVEN BY NORTH-ATLANTIC OCEAN CIRCULATION

RECENT data from the GRIP ice core1-3 in Greenland suggest that the cl imate of the last (Eemian) interglacial period was much less stable th an that of the present interglacial. Rapid transitions between warm an d cold periods were found to occur on timescales of just a few decades . The North Atlantic climate during the Eemian period was also shown t o be characterized by three states, respectively warmer than, similar to and colder than today1,2. Recent data from the nearby GISP2 ice cor e have revealed some discrepancies with these findings, which remain t o be resolved4,5. Here we present simulations using an idealized globa l ocean model, which suggest that the North Atlantic ocean has three d istinct circulation modes, each of which corresponds to a distinct cli mate state. We find that adding a simple random component to the mean freshwater flux (which forces circulation) can induce rapid transition s between these three modes. We suggest that increased variability in the hydrological cycle associated with the warmer Eemian climate could have caused transition between these distinct modes in the North Atla ntic circulation, which may in turn account for the apparent rapid var iability of the Eemian climate.