HR: 09:00h
AN: PP21E-05    [Abstracts]
TI: Sustained Thermohaline Shutdown and Sea ice Advance in a Global Climate Model Forced with Freshwater During an LGM Climate
AU: * Bitz, C M
EM: bitz@atmos.washington.edu
AF: Atmospheric Sciences, University of Washington, Box 351640, Seattle, WA 98195-1640 United States
AU: Chiang, J
EM: jchiang@atmos.berkeley.edu
AF: Dept. of Geography, University of California, Berkeley, 547 McCone Hall, Berkeley, CA 94720-4740 United States
AB: Shutdown of the thermohaline circulation by freshwater hosing is usually only temporary in sophisticated climate models: Once hosing ends, the circulation recovers in a few decades. Hosing in these experiments begins under roughly modern climate conditions. However, when hosing is initiated from an LGM climate with the Community Climate System Model, the THC is nearly shutdown and stays drastically reduced for over a century after the hosing ends. The corresponding reduction in ocean heat transport causes wintertime sea ice to advance as much as 20° latitude in the North Atlantic with profound surface air cooling. The surface air temperature over Greenland is more than 5° C colder annually 100 yrs after hosing in the LGM climate, while the temperature is essentially normal after 50 yrs in a comparable modern hosing experiment with the same model. The THC shutdown in the LGM climate persists because the freshwater anomaly at the surface dissipates very slowly compared to the modern hosing experiment. The freshwater anomaly is dispersed horizontally in either case, but surprisingly it is also dispersed vertically in the modern hosing experiment. Therefore the initial stable stratification from the hosing is eroded in a matter of decades and the THC recovers rather quickly in the modern case. The slow and modest recovery to the hosing in the LGM experiment is punctuated by one significant abrupt warming event after a century associated with eventual weakening of the stratification in the Greenland and Norwegian Seas. We compare and contrast this abrupt event with an abrupt event in a 21st century global warming scenario that occurred in just one of ten ensemble members with CCSM.
DE: 0750 Sea ice (4540)
DE: 1621 Cryospheric change (0776)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005