PP13D-02:
AMOC Evolution in the Last Deglaciation: Forcing Mechanism, Thermohaline Instability and Implications
Monday, 15 December 2014: 1:55 PM
Zhengyu Liu1, Wei Liu2,3, Jiang Zhu1 and Esther C Brady4, (1)Univ Wisconsin Madison, Madison, WI, United States, (2)UW-Madison, Madison, WI, United States, (3)Scripps Institution of Oceanography, La Jolla, La Jolla, CA, United States, (4)National Center for Atmospheric Research, Boulder, Boulder, CO, United States
Abstract:
The forcing mechanism and instability of the Atlantic Meridional Overtuning Circulation (AMOC) over the last 21,000 years is studied using transient simulations under realistic forcings in the NCAR-CCSM3. First, in addition to the strong millennial AMOC variability forced by melting water fluxes, the background AMOC is determined by two opposing effects: the intensification by the rising atmospheric CO2 and the reduction by the retreating ice sheet, both through the sea ice feedbacks in the North Atlantic. As a result, the AMOC strength does not change significantly after the deglaciation. Second, the model AMOC exhibits a monostable behavior. This monostable AMOC, which has been observed in almost all state-of-art coupled general climate models (CGCMs), is likely to be caused by a systematic model bias that is associated with the tropical bias, the resulted freshwater flux and AMOC freshwater export. This AMOC over-stabilization bias needs to be improved in these CGCMs to allow for a credible projection of AMOC evolution in the future.
