SURFACE WATER RESPONSE OF THE EQUATORIAL ATLANTIC OCEAN TO ORBITAL FORCING

The response of the mixed layer of the equatorial Atlantic to climate change, for times greater than 10 kyr, is predominantly forced by the precessional component of insolation. A zonal transect of three cores analyzed at 1-kyr intervals documents this response for 0-250 ka The western equatorial Atlantic is characterized by minimal variation in surface water character, indicating temporal stability of the mixed layer, except during intervals of maximum glaciation. In contrast, the eastern region shows marked temporal variations in estimated sea surface temperature and foraminiferal assemblages, with dominant periodicities centered on 23 kyr. At precessional periods, the eastern equatorial Atlantic responds in phase with southern hemisphere sea surface temperature and significantly leads northern hemisphere sea surface temperature and continental ice volume. These signals are the product of orbitally forced variations in (1) trade wind and monsoon-controlled divergence and (2) advection of heat from high southern latitudes.