NUTRICLINE VARIATION IN THE EQUATORIAL ATLANTIC COINCIDENT WITH THE YOUNGER DRYAS

Variations in nutricline depth during the last deglaciation are recorded by the phytoplankton species Florisphaera profunda. A stacked record of six deep-sea cores shows that across the entire equatorial Atlantic there was a brief shallowing of the nutricline, centered on 11 ka, coincident with the Younger Dryas. This shallowing is linked with high-latitude North Atlantic deglacial events. W e invoke high albedo and cool sea surface temperatures in the northern latitudes during 11 ka which steepened an already higher-than-expected winter insolation (and hence temperature) gradient for a time of June perihelion. We postulate that the resultant increased pressure gradient caused an intensification of the northern hemisphere winter tropical easterlies which in turn caused equatorial divergence to occur in boreal winter.