HR: 14:10h
AN: PP53C-03 INVITED     [Abstracts]
TI: Bracketing the Warm Peak Phases of the Middle Pliocene Climate
AU: * Dowsett, H J
EM: hdowsett@usgs.gov
AF: US Geological Survey, 926A National Center, Reston, VA 20192 United States
AU: Chandler, M A
EM: mac59@columbia.edu
AF: GISS at Columbia University, 2880 Broadway, New York, NY 10025 United States
AU: Dwyer, G S
EM: gsd3@duke.edu
AF: Earth and Ocean Sciences, 103 Old Chemistry Building Duke University, Durham, NC 27708 United States
AU: Cronin, T M
EM: tcronin@usgs.gov
AF: US Geological Survey, 926A National Center, Reston, VA 20192 United States
AB: Estimates of sea surface temperature (SST) from ocean cores reveal a warm phase of the Pliocene between about 3.3 and 3.0 Ma. Pollen records from land-based cores and sections, although not as well-dated, also show evidence for a warmer climate at about the same time. Increased greenhouse forcing and altered ocean heat transports are the leading candidates for the underlying cause of Pliocene global warmth. Despite being a general period of global warmth, considerable SST variability exists within this interval. Two new SST reconstructions have been created to provide a climatological error bar for warm peak phases of the Pliocene. GISS GCM simulations that use the new "bracketing" SST reconstructions show the significant potential variability that existed during the relatively warm middle Pliocene, even when we only consider the difference between the various warm peak phases of the original PRISM time slab. While even the smallest warm peak of this period yields a significantly warmer climate than modern (+2.1C in January) the difference between the maximum and minimum warm phases (delta 1.1C in January) is a significant portion of the overall Pliocene-Modern anomaly. This implies that middle Pliocene climates could have cycled from climates that were much nearer the modern to those that were more like the warm middle Pliocene exhibited by numerous simulations conducted using the "peak-average" PRISM SST data during the past decade. The key question is what could have led to the cycling (and more importantly, is it something that could occur in the future)? Obviously, primary suspects include greenhouse gas changes and orbital cycling. However, positive feedbacks in the moisture balance over the North Atlantic, which show up in the results from GISS GCM simulations with the new SST reconstructions, suggest the importance of continuing to pursue coupled ocean-atmosphere experiments for this time period.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1600 GLOBAL CHANGE (New category)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting