HR: 1330h
AN: PP12A-0229    [PDF]
TI: Last Glacial Maximum Sea-Surface Temperatures - Sensitivity to Uncertainties and Change in the Tropical and Subtropical Ocean: Modeling results
AU: * Hostetler, S
EM: steve@coas.oregonstate.edu
AF: US Geological Survey, Department of Geosciences Oregon State University, Corvallis, OR 97331
AU: Pisias, N
EM: pisias@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331
AU: Mix, A
EM: mix@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331
AB: To assess the effects of regional biases in sea-surface temperature (SST) estimates on the climatology of the LGM we have conducted a suite of simulations with the GENESIS climate model in which the only changes from nominal LGM boundary conditions (continental ice, atmospheric composition, orbital parameters) are new SST fields. We compare four simulations: 1) an LGM that uses previously published SSTs, 2) a simulation in which LGM subtropical SSTs are modified (STROP), 3) a simulation in which tropical, and in particular the Western Pacific Warm Pool, temperatures are modified (WPOOL), and 4) a combined simulation in which both tropical and subtropical temperatures are modified (COMB). On an annual basis, similar temperature responses over the mid- and high-latitude continents are induced by the WPOOL and STROP SST fields. Within the tropics, however, the continents are more sensitive to cooling of the warm pool in the WPOOL SST field. Both the WPOOL and the COMB SST fields improve agreement between simulated global air temperature and geologic data, particularly in the tropics. The WPOOL experiment produces tropical cooling (glacial versus present) over land and ocean of 6.5$^{o}$ and 4.0$^{o}$C, respectively, yielding values comparable to those obtained by the mixed-layer models evaluated by PMIP. Air temperatures in the COMB experiment are in better agreement globally with terrestrial data, however cooling over tropical land and oceans is 7.5$^{o}$C and 5.2$^{o}$C, respectively. These changes exceed those of the coldest PMIP simulations and some fully coupled A/OGCM simulations by over a degree, but agree with oceanic cooling achieved in two coupled A/OGMC simulations. The wide spread in the magnitude of tropical cooling simulated by the various models provides no definitive consensus as to what the LGM climatology of the tropics really was. Modifying the SST fields in the WPOOL and COMB experiments repositions the sites of tropical convection and shifts patterns of terrestrial net moisture over both the tropics and the midlatitudes. Global precipitation is more sensitive to SST changes at low latitudes (WPOOL and COMB) than and mid latitudes (STROP) or at high latitudes (the nominal LGM run). The tropics in both experiments remain drier than present overall. Cooler air temperatures and regional increases in net moisture in the WPOOL and COMB experiments would support more positive mass balance of glaciers throughout the tropics. Substantially more positive mass balances (precipitation minus evaporation and runoff) are also indicated over the southern margins of the Laurentide and Fennoscandian ice sheets in the WPOOL and COMB experiments, while both ice sheets display more negative balances over their interiors. We are exploring model sensitivity to other temperature configurations and we will present more detailed analyses of the mass balance and other climatic fields in this talk.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting