THE YOUNGER DRYAS TERMINATION AND NORTH-ATLANTIC DEEP-WATER FORMATION- INSIGHTS FROM CLIMATE MODEL SIMULATIONS AND GREENLAND ICE CORES

Results from the GISP2 and GRIP ice cores show that the termination of the Younger Dryas (YD) climate event in Greenland was a large and ext remely fast climate change. A reinitiation of North Atlantic Deep Wate r formation following a shutdown, and its associated winter release of heat to the atmosphere, has been suggested as the most likely cause o f this climate transition. To test this idea, two general circulation model experiments using GENESIS have been completed for YD time (12,00 0 calendar years ago): one with low heat flux in the Nordic Seas (10 W /m(2), deep water shutdown) and one with high Nordic Sea heat flux (30 0 W/m(2), active deep water formation). Comparison of Greenland climat e differences between these experiments with the ice core records show s that when deep water is turned on, much of the YD termination warmin g is achieved. The increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation, which o bscures the dominantly wintertime response to the specified forcing. T he winter storm track shift toward Greenland contributes much of the c limate change at the YD termination.