5.4
Dansgaard-Oeschger-like climate states in a coupled GCM
PAPER WITHDRAWN
Ian Eisenman, California Institute of Technology, Pasadena, CA; and E. Tziperman and C. Bitz
The last glaciation (80-10 kyr BP) was punctuated by dramatic switches between warm and cold climates characterized by abrupt warming events recorded in Greenland ice cores. A leading hypothesis attributes these Dansgaard-Oeschger (DO) events to internal variability in the North Atlantic meridional overturning circulation (MOC), but theories have struggled to explain how these changes in MOC are capable of inducing such a large signal in Greenland. We present the results of two simulations using the CCSM3 coupled atmosphere-ocean-sea ice model. Both simulations are forced by land ice distributions characteristic of typical glacial conditions, but one simulation begins with a warm interglacial ocean and sea ice initial condition, while the other has a cold ocean and sea ice initial condition based on Last Glacial Maximum conditions. The simulations settle into what appears to be two quasi-steady states which persist for roughly 700 years before both simulations converge on a single state. The two states differ in North Atlantic sea ice and surface temperature, and the difference between the two states compares favorably with proxy reconstructions of the difference between the warm and cold phases of DO cycles. These results suggest that the glacial climate may be able to sustain multiple long-lived states of sea ice cover and ocean circulation which resemble the two phases of DO cycles.
Session 5, Air-sea interaction in paleo-climates
Tuesday, 21 August 2007, 8:30 AM-9:45 AM, Broadway-Weidler-Halsey
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