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 extremely fast climate change. A reinitiation of North Atlantic Deep Water formation following a shutdown, and its associated winter release of heat to the atmosphere, has been suggested as the most likely cause of this climate transition. To test this idea, two general circulation model experiments using GENESIS have been completed for YD time (12,000 calendar years ago): one with low heat flux in the Nordic Seas (10 W/m², deep water shutdown) and one with high Nordic Sea heat flux (300 W/m², active deep water formation). Comparison of Greenland climate differences between these experiments with the ice core records shows that when deep water is turned on, much of the YD termination warming is achieved. The increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation, which obscures the dominantly wintertime response to the specified forcing. The winter storm track shift toward Greenland contributes much of the climate change at the YD termination.