HR: 09:00h
AN: PP21C-05 INVITED     [Abstracts]
TI: Tropical Atlantic Upwelling and SST Changes associated with the mid-Pliocene onset of glacial cycles
AU: * deMenocal, P B
EM: peter@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Route 9W, Palisades, NY 10964 United States
AU: Philander, S G
EM: gphlder@princeton.edu
AF: Dept. of Geosciences, Princeton University, Princeton, NJ 08540 United States
AU: Lynch-Steiglitz, J
EM: jean@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Inst. Technology, Atlanta, GA 30332 United States
AU: Raymo, M
EM: raymo@bu.edu
AF: Dept. of Earth Sciences, Boston University, Boston, MA 02215 United States
AB: Dynamical models examining the sensitivity of coupled tropical ocean-atmosphere processes to imposed boundary condition changes have proposed that late-Pliocene onset of glacial cycles near 3 Ma may have resulted from cooling and shoaling of the mean depth of the tropical thermocline. To test these ideas we measured proxies for upwelling, photic zone thermal gradients, and SSTs at eastern equatorial Atlantic Site 662 and compared these data to benthic d18O measured on the same samples. Our results show that the tropical Atlantic thermocline shoaled, cooled, and became responsive to orbital obliquity forcing after 2.9 Ma, in agreement with these hypotheses. Upwelling cycles led ice volume changes by 6-8 ka and maximum upwelling was in-phase with maximum annual equatorial insolation. Mg/Ca meaasurements of G. ruber indicate that SSTs also cooled and became more variable after 2.9 Ma. In agreement with theory, the mid-Pliocene warm period (ca. 3.0-3.3 Ma) was characterized by a deep, warm thermocline in the tropical Atlantic and Pacific. These results support recent observations that the tropics may have contributed to the late Pliocene onset of globally cooler and more variable climates. The onset of strong precessional variability which characterizes late Pleistocene upwelling records appears to have commenced after 2 Ma and it appears to reflect further shoaling and cooling of the tropical thermocline.
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 4279 Upwelling and convergences
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting