HR: 09:30h
AN: PP51E-07    [Abstracts]
TI: The Late Pliocene Tropical Pacific
AU: * MEDINA-ELIZALDE, M A
EM: martinmedina@umail.ucsb.edu
AF: University of California, Santa Barbara, SANTA BARBARA, CA 93106, United States
AU: LEA, D W
EM: lea@geol.ucsb.edu
AF: University of California, Santa Barbara, SANTA BARBARA, CA 93106, United States
AB: To test the permanent El Niño hypothesis and to investigate the character of tropical climate variability during the Pliocene, we used Mg-Paleothermometry in the planktonic foraminifer Globigerinoides ruber to reconstruct detailed thermal and d18O-seawater histories from ODP site 806B, in the western equatorial Pacific (WEP). Our records span the Late Pliocene between 2.3 and 3.1 Ma with an average resolution of 1.7 ky. Hole 806B G. ruber Mg/Ca-derived SST data indicate an average Late Pliocene SST of 28°C, a modest long-term cooling of 0.3°C and a glacial to interglacial SST range of 2°C. Our western equatorial Pacific SST record shows spectral characteristics previously unknown or unreported. In contrast with foraminiferal d18O records which show a dominant 41 ky-period component during the Late Pliocene, our WEP SST record shows a dominant ~100 ky-period component and a weaker contribution at 41 ky. Cross-spectral analysis reveals that SST leads ODP Hole 806B benthic foraminiferal d18O by 7.4 and 1.9 ky at the ~100 ky and 41 ky-dominant periods during the Late Pliocene. Comparison between our Hole 806B SST record with an ODP Hole 846 SST record from the eastern equatorial Pacific (EEP) cold tongue suggests that both records are coherent and dominated by 100 ky cycles and a weaker contribution at 41 ky. Furthermore, comparisons between these records indicate a ~3° C east-west zonal equatorial Pacific SST gradient and the strengthening of this gradient from 3° C to 4° C between 3.1 and 2.3 Ma. Our results are not compatible with the notion of a permanent El Niño state in the Late Pliocene. The character of Tropical Pacific thermal evolution, with a dominant 100 ky period and a weaker contribution at 41 ky observed in both eastern and western equatorial Pacific SSTs, suggests that the dominant driver of this variability was radiative forcing by atmospheric greenhouse gases. The larger glacial-interglacial amplitudes observed in eastern equatorial Pacific SSTs suggests an additional influence of EEP thermocline changes on EEP SSTs, as previously suggested (Lawrence et al., 2006).
DE: 1051 Sedimentary geochemistry
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting