Antarctic Intermediate Water Variability in the South Atlantic Over the Last 600,000 years

Abstract Despite its importance as a key component of the Atlantic Meridional Overturning Circulation, the long‐term variability of Antarctic Intermediate Water (AAIW) remains poorly constrained due to the lack of adequate proxy records. To address this, we present the longest reconstruction of AAIW variability in the South Atlantic using authigenic (foraminifera and sediment leachates) neodymium (Nd) isotopes complemented with a benthic foraminiferal δ 13 C record from Deep Sea Drilling Project (DSDP) Site 516 on the Rio Grande Rise from 1,313 m water depth within the core of AAIW today. By comparison of DSDP Site 516 detrital and authigenic Nd isotope records with those from neighboring DSDP Site 517 bathed in North Atlantic Deep Water (NADW), we demonstrate that the Nd isotope signals obtained from mixed planktonic foraminifera from this open ocean pelagic setting reliably recorded past intermediate water mass mixing. The authigenic Nd isotope record and the benthic δ 13 C data show consistent glacial‐interglacial variability over the last 600 kyr. More radiogenic Nd isotope values and lower benthic δ 13 C signatures during glacial periods point to the reduced admixture of unradiogenic NADW into Circumpolar Deep Water during glacials. The glacial‐interglacial variability seen in our Nd isotope record is consistent with other AAIW records from the Southeast Atlantic, Indian and the Southwest Pacific Oceans suggesting an essentially uniform southern‐sourced AAIW signal transported northwards at intermediate depth through the three major Ocean basins. The new record shows AAIW shifted to more radiogenic values during the MIS 14 glacial in contrast to Nd isotope records of NADW.