North Atlantic melting water forcing of early Pacific deglacial warming and two-step North Pacific ventilation: a transient GCM study with CCSM3

The dramatic deglaciation climate evolution provides a key observation for studying the role of ocean circulation on deglacial CO2 rise and for testing climate models. Here, we present the first transient climate simulation of the deglaciation evolution from the last glacial maximum to the early Holocene in a synchronously coupled general circulation model - CCSM3. Our model simulates the major features of deglaciation evolution. In polar region, the deglacial warming trends from Greenland and Antarctic are well captured in the simulation mainly as the response to CO2 increase, while the warming trend in Greenland had been interrupted by the millennial events caused by the variability of the Atlantic Meridional Overturning Circulation (AMOC). In North Pacific, the evolution of sea surface temperature (SST) mimics the evolution of the Greenland due to the atmospheric teleconnection. In South Pacific, the onset of deglacial warming occurred asynchronously at the surface: the warming started at 20ka in the southern ocean due to orbital forcing and at 17ka in the tropics due to CO2 rise. At intermediate and deep Pacific ocean, the onset of the early deglacial warming occurred synchronously at 19ka. Sensitivity experiments were performed to demonstrate North Atlantic melting water forcing was causing the early deglacial warming of intermediate and deep Pacific. Due to the atmospheric teleconnection, North Atlantic melting water forcing also induced two major ventilation events in North Pacific during Heinrich event 1 and Younger Dryas with reduced ventilation during Bølling-Allerød. In the southern ocean, the ventilation was reduced due to the surface warming and reduced salinity caused by the reduction of brine ejection from sea ice. The three degree warming of intermediate and deep Pacific and the two-step ventilation of the North Pacific are two major features of the deglacial evolution in the Pacific basin and their implications for the deglacial atmospheric CO2 rise will be discussed.