HR: 1330h
AN: PP22A-1205    [PDF]
TI: Simulated Response of Tropical Climate to Changes in ice Sheet and Carbon Dioxide Forcings
AU: * Foster, T M
EM: tmfoster@umich.edu
AF: Department of Geological Sciences University of Michigan, 425 E. University Ave., Ann Arbor, MI 48104 United States
AU: Poulsen, C J
EM: poulsen@umich.edu
AF: Department of Geological Sciences University of Michigan, 425 E. University Ave., Ann Arbor, MI 48104 United States
AB: Proxy records indicate that the tropical climate has experienced substantial changes that appear to coincide with Dansgaard-Oeschger and glacial-interglacial climate changes in the northern hemisphere. The source of the tropical climate variability is debated. To date, climate models have exhibited a relatively minor tropical climate response to northern hemisphere extratropical forcing. To further explore the influence of northern hemisphere extratropical forcing on tropical climate, a series of coupled ocean-atmosphere experiments using the Fast Ocean-Atmosphere Model have been performed to test the influence of the Laurentide Ice Sheet, and the post-glacial CO2 rise on tropical climate. The control experiment is a Last Glacial Maximum simulation (including ice-sheet configuration, orbital parameters, land surface characteristics, and trace gas concentrations appropriate for 21k). Two additional experiments have been conducted, the first with an 11k ice-sheet configuration and the second with an 11k ice-sheet configuration and 280 ppm CO2. All other boundary conditions remain constant in these sensitivity experiments. Preliminary model results indicate that the extratropical forcing has a substantial effect on tropical climate and the ITCZ. Deglaciation causes a pronounced (5-10\deg latitude) northward shift in the position of the ITCZ. This in turn has an effect on SST and thermocline structure in the Pacific, leading to changes in the periodicity and magnitude of interannual and interdecadal variability. The tropical Pacific warms 2-3\deg C in the LGM simulation compared to the 11k ice-sheet experiment, whereas a cooling of 10\deg C in the Southern Ocean, south of Australia, occurs between the same two experiments. Furthermore, the Asian monsoon appears to be affected by the change in glacial boundary conditions with stronger convective precipitation during times of full glaciation. Model results demonstrate that extratropical forcing may have caused significant climate changes in the tropics.
DE: 1620 Climate dynamics (3309)
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 4522 El Ni¤o
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting