| Summary: | Sea-surface temperature (SST) and salinity (SSS) records obtained from two deep-sea cores have been used to reconstruct meridional gradients in the mid-latitude North Atlantic over the past 40 k.y. During the buildup of ice sheets toward the last glacial maximum, SST and SSS gradients between 40°and 50°N increased by 6-8°C and ~2‰, respectively. This trend represents a two-fold increase in surface-water gradients between 40 and 20 ka and strongly over-prints the signal of high-frequency climatic oscillations. We attribute the gradual intensification of meridional SST and SSS gradients to a precession-driven increase in advection within the glacial North Atlantic Current resulting from changes in low-latitude insolation and seasonality. A strongly zonal ocean circulation pattern, maintained by greater advection and enhanced heat storage within the subtropical ocean at the last glacial maximum, persisted until ca. 20 ka, when a decrease in glacial SST gradients, coincident with a reduction in low-latitude climate forcing, marked the initiation of the last deglaciation.
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