TRADE-WIND FORCING OF UPWELLING, SEASONALITY, AND HEINRICH EVENTS AS A RESPONSE TO SUB-MILANKOVITCH CLIMATE VARIABILITY

Planktonic foraminifera recovered from two cores in the northern Bengu ela upwelling system reveal a history of rapid events with a variabili ty at sub-Milankovitch frequencies during the last 140 kyr, The ''cold -water'' planktonic foraminifer, left coiling Neogloboquadrina pachyde rma (Ehrenberg), shows rapid fluctuations in relative abundance, indic ating changes in upwelling: intensity. The periods of high abundance i n left coiling N. pachyderma are referred to as ''PS events'' (pachyde rma sinistral) and indicate increased intensity and zonality of the So uth Atlantic trade winds controlling the Benguela upwelling system. Th e good correlation between PS events, the North Atlantic Heinrich even ts, and the Dansgaard-Oeschger cycles from the Greenland Ice Sheet Pro gram (GISP2) ice core suggests large-scale global oceanographic or cli matic teleconnections between the South and North Atlantic via the tra de wind system. The radiocarbon constrained timing of PS events younge r than 45 kyr indicates that the South Atlantic leads the North Atlant ic's response to trade wind changes, particularly during isotope stage s 4-2 when the Earth was dominated by large ice sheets. At times of in creased trade wind strength, tropical and subtropical waters are force d across the equator enhancing the pool of warm water to be transferre d to the high latitudes of the North Atlantic via the Gulf Stream and North Atlantic Drift, increasing the pull of the thermohaline convecti ve conveyor, The increased supply of wan water to the polar regions of the northern hemisphere increases the ice-ocean moisture gradient and accelerates ice sheet growth, leading to eventual instability and col lapse.