HR: 1600h
AN: PP24A-01 INVITED    [Abstracts]
TI: Changes in Attitude on Equatorial Latitudes: Tropical Climate Evolution During the Ice Ages
AU: * Lea, D W
EM: lea@geol.ucsb.edu
AF: University of California, Department of Earth Science, Santa Barbara, CA 93106,
AB: Some 50 years ago, Cesare Emiliani published the first oxygen isotope records from marine sediment cores taken in the Caribbean Sea. He interpreted the observed oscillations as a consequence of 6 deg cooler tropical sea surface temperatures (SSTs) during the Ice Ages. In the following decades, this interpretation was discarded in favor of the dominant role of high latitude ice volume on oxygen isotope variability. Consequently, and as bolstered by a lack of faunal evidence for significant tropical changes, the Ice Ages were regarded as largely high and mid latitude phenomenon, with minimal involvement of the tropics. This view began to change when evidence emerged from terrestrial archives, from new proxies of tropical SST, and from tropical sites with rapidly accumulating sediments such as the Cariaco Basin, for an active climate role for the tropics on both orbital and millennial timescales. Today it is largely accepted that tropical SSTs cooled by about 3 deg during glacial episodes, and that at least some parts of the tropics played a dynamical role in the abrupt millennial scale events first identified in high latitude ice cores. What is still controversial is: 1) the timing of tropical changes, with some records strongly suggesting that tropical changes pre-dated northern hemisphere high latitude changes, including ice volume changes; 2) the climate forcing that drove tropical changes, with greenhouse gas forcing and high latitude shifts the most likely sources; and 3) the role of the tropics in triggering, amplifying or even driving large scale climate evolution. This talk will address these three critical questions and survey the most recent evidence. In particular, I will present new evidence that supports an early deglacial warming of the tropics in response to greenhouse gas forcing. If this interpretation is correct, it suggests that tropical warming might have played a key role in driving deglaciation. It also suggests that past tropical changes under known forcing can be used to gauge climate sensitivity, both in the narrow sense of temperature response, and in the broad sense of how tropical climate and circulation evolved. Ultimately, I will argue that tropical paleoclimate records inform predictions of how both the tropics and the global climate system will respond to rising greenhouse gases in the atmosphere.
UR: http://www.geol.ucsb.edu/faculty/lea/
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4924 Geochemical tracers
DE: 4926 Glacial
DE: 4930 Greenhouse gases
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting