Variations in deep water masses along the western margin of South Africa, spanning the last two glacial terminations

Abstract

The neodymium isotope composition (εNd) of planktic foraminifera and the relative abundances and δ13C of the benthic foraminiferal species C. wuellerstorfi from two gravity cores, retrieved from the western margin of South Africa, provide a late Quaternary (MIS 6 to MIS 1) record of the variations in North Atlantic Deep Water (NADW) and Southern Component Water (SCW). The εNd records from cores at water depths of 3522 m and 3631 m reveal a strong influence of SCW (Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW)) during the peak glacial periods of MIS 6 (εNd = −8.75 to −7.35) and MIS 2 (εNd = −8.44 to −7.27). The strength of the SCW influence decreases while that of the NADW increases during glacial terminations (GT) II (εNd = −10.61 to −9.99) and GT I (εNd = −10.75 to −9.67). More radiogenic εNd values along the flow path of NADW are interpreted to indicate the weakening of NADW penetration southward, as a result of decreasing deep water formation in the North Atlantic during peak glacial periods. The relative abundance and δ13C of C. wuellerstorfi are greater during glacial terminations and interglacials than during peak glacial periods, which is consistent with the less radiogenic εNd values following GT II and GT I. These results suggest that C. wuellerstorfi abundances can be a useful indicator of deep water masses when combined with εNd and δ13C records.