HR: 08:00h
AN: PP21C-01 INVITED     [Abstracts]
TI: The Pliocene Paradox
AU: * Fedorov, A
EM: alexey.fedorov@yale.edu
AF: Yale University, Department of Geology and Geophysics, PO Box 208109, New Haven, CT 06520
AU: Philander, G
EM: gphlder@princeton.edu
AF: Princeton University, AOS Program, 205 Sayre Hall, Forrestal Campus, Princeton, NJ 08540
AU: Pacanowski, R
EM: ron.pacanowski@noaa.gov
AF: Geophysical Fluid Dynamics Laboratory, Route 1, Forrestal Campus, Princeton, NJ 08540
AB: The early Pliocene, roughly 5 to 3 million years ago (Ma), was paradoxical in being both similar to, and also very different from the world of today. The distribution of continents and the atmospheric concentration of carbon dioxide were essentially what they are today, but globally averaged surface temperatures were approximately 3$^{o}$C higher. A key contributor to those warmer conditions was a perennial El Ni\~{n}o with surface waters of the equatorial Pacific as warm in the east as in the west. Other factors included the absence of major coastal upwelling regions - off the coasts of California and South-West Africa. Such conditions were possible because, presumably, the thermocline was so deep that the winds were unable to bring cold water to the surface. Studies of the oceanic circulation indicate that the maintenance of such a deep tropical thermocline requires surface waters in low latitudes to be as dense as in high latitudes. A small or zero equator-to-pole density gradient implies a weaker than today meridional temperature gradient but stronger meridional salinity gradient. This is favored by rainfall that is low in the subtropics, and high in subpolar regions, causing surface salinities to decrease with latitude. Thus, permanent El Ni\~{n}o conditions could prevail in the early Pliocene because salinity and temperature had the same (but opposite) effect on density. The subsequent gradual global cooling led to an increase in the meridional density gradient and resulted in a shallower thermocline. This terminated the perennial El Ni\~{n}o, introduced La Ni\~{n}a, and caused a reorganization of the wind-driven oceanic circulation that can account for various climate changes at that time. This study interprets the Pliocene paradox as an indicator that, at present, the global climate is sensitive to modest changes in latitudinal sea surface density gradients.
UR: http://www.geology.yale.edu/$\sim$avf5/publications
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 4522 El Ni¤o
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting