North Atlantic Intermediate to Deep Water circulation and chemical stratification during the past 1 Myr

Abstract

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 glacial intervals, significant increases in intermediate‐to‐deep δ 13 C gradients (commonly reaching >1.2‰) are consistent with changes in deep water circulation and associated chemical stratification. Bathymetric δ 13 C gradients covary with benthic foraminiferal δ 18 O and covary inversely with Vostok CO 2 , in agreement with chemical stratification as a driver of atmospheric CO 2 changes. Three deep circulation indices based on δ 13 C show a phasing similar to North Atlantic sea surface temperatures, consistent with a Northern Hemisphere control of NADW/SOW variations. However, lags in the precession band indicate that factors other than deep water circulation control ice volume variations at least in this band.