The Role of Wind-Driven Oceanic Circulation in Climate Changes

S. George Philander, (Princeton University, NJ 08544-1003; ph. 609-258-4100; fax#609-258-5275; Internet: gphlder@splash.princeton.edu)

The processes that determine sea surface temperature variations, which profoundly affect the atmospheric circulation and hence the Earth's climate, depend on the time-scale under consideration: (i) seasonal and interannual variations involve a shallow surface layer of the ocean in which heat fluxes across the ocean surface, and a horizontal redistribution of warm surface waters in the tropics (as occurs during El Nino) are of paramount importance; (ii) decadal fluctuations are strongly influenced by the shallow, meridional circulation of the "ventilated" thermocline, between the surface and a depth of a few hundred meters, that involves wind-driven oceanic exchanges between the tropics and extra-tropics; (iii) centennial variations depend on the thermohaline circulation that controls the properties of the ocean below the thermocline. The processes involved in (i) and (ii) are of central importance to phenomena such as the cooling of the surface waters of the tropics during the last glacial maximum some 18,000 years ago, and the abrupt onset of climate changes that occur within a few decades.