345,000-year-long multi-proxy records off South Africa document variable contributions of Northern versus Southern Component Water to the Deep South Atlantic

Abstract

Millennial to multi-centennial benthic foraminiferal stable isotope, sortable silt mean grain size (SS―) and benthic foraminiferal Cd/Ca records are presented for core MD96-2080 from 2488 m water depth at the western Agulhas Bank Slope off South Africa. The data demonstrate the interplay between Northern and Southern Component Waters as the Atlantic Meridional Overturning Circulation (MOC) shifted between glacial and interglacial modes. During early phases of Marine Isotope Stages (MIS) 6 and 8, the Atlantic MOC was little different from its interglacial mode. Benthic foraminiferal δ13C modulation during these stages can be explained by mean-ocean δ13C changes, while, only subtle benthic foraminiferal Cd/Ca increases indicate a continued influence of Northern Component Waters (NCW). Later glacial stages are characterized by a progressive incursion of nutrient-enriched waters presumably a mixture of Upper and Lower Southern Component Waters (SCW). Maximum SS― values during late glacial ventilation minima suggest increased near-bottom flow speeds. The combined ventilation and flow-speed pattern indicates an enhanced influence of SCW, most likely linked with a northward migration of the Antarctic Circumpolar Current (ACC) which progressively decreased the influence of NCW at site MD96-2080. Peak-maximum seawater Cd concentrations (Cdsw, derived from benthic foraminiferal Cd/Ca) overlap in time with increased deposition of ice-rafted debris (IRD) in the North Atlantic and plot outside the δ13C/Cdsw field in the South Atlantic. The anomalies conceivably are the South Atlantic equivalents of peak Cdsw maxima associated with Heinrich-type events in the North Atlantic and reflect a substantially reduced Atlantic MOC.