Precessional forcing of productivity in the North Atlantic Ocean

The sedimentary C-37 alkenone fluxes in core SU90/08 situated in the North Atlantic (43 degrees N) showed that export productivity related to some Hap tophyta was driven by precession (1/23 kyr(-1)) in the last 260 kyr during the glacial periods. In the interglacial stages these alkenones were strong ly depleted. This different behaviour is attributed to the displacement of Ekman pumping to lower latitudes and to thermocline stability decreases in the glacial periods. The alkenones were coherent and nearly phased with bor eal winter insolation, suggesting a link between productivity and the stren gth of the westerlies. They were also coherent with the precessionally driv en nutriocline minima and winter sea surface temperature in the equatorial Atlantic Ocean. The combination of the measurements at these different lati tudes point to a strong coupling in the dynamics of the Hadley and Ferrel c ells and to a dominant North Atlantic modulation of marine productivity to precession during the glacial stages.