North Atlantic intermediate to deep water circulation and chemical stratification during the past 1 Myr

Benthic foraminiferal carbon isotope records from a suite of drill sites in the North Atlantic are used to trace variations in the relative strengths of Lower North Atlantic Deep Water (LNADW), Upper North Atlantic Deep Water (UNADW), and Southern Ocean Water (SOW) over the past 1 Myr. During glacia l intervals, significant increases in intermediate-to-deep delta(13)C gradi ents (commonly reaching >1.2 parts per thousand) are consistent with change s in deep water circulation and associated chemical stratification. Bathyme tric delta(13)C gradients covary with benthic foraminiferal delta(18)O and covary inversely with Vostok CO2, in agreement with chemical stratification as a driver of atmospheric CO2 changes. Three deep circulation indices bas ed on delta(13)C show a phasing similar to North Atlantic sea surface tempe ratures, consistent with a Northern Hemisphere control of NADW/SOW variatio ns. However, lags in the precession band indicate that factors other than d eep water circulation control ice volume variations at least in this band.