Late Pleistocene deep-water circulation in the subantarctic eastern Atlantic

Abstract

We present three new benthic foraminiferal δ 13C, δ 18O, and total organic carbon time series from the eastern Atlantic sector of the Southern Ocean between 41°S and 47°S. The measured glacial δ 13C values belong to the lowest hitherto reported. We demonstrate a coincidence between depleted late Holocene (LH) δ 13C values and positions of sites relative to ocean surface productivity. A correction of +0.3 to +0.4 [‰ VPDB] for a productivity-induced depletion of Last Glacial Maximum (LGM) benthic δ 13C values of these cores is suggested. The new data are compiled with published data from 13 sediment cores from the eastern Atlantic Ocean between 19°S and 47°S, and the regional deep and bottom water circulation is reconstructed for LH (4–0 ka) and LGM (22–16 ka) times. This extends earlier eastern Atlantic-wide synoptic reconstructions which suffered from the lack of data south of 20°S. A conceptual model of LGM deep-water circulation is discussed that, after correction of southernmost cores below the Antarctic Circumpolar Current (ACC) for a productivity-induced artifact, suggests a reduced formation of both North Atlantic Deep Water in the northern Atlantic and bottom water in the southwestern Weddell Sea. This reduction was compensated for by the formation of deep water in the zone of extended winter sea-ice coverage at the northern rim of the Weddell Sea, where air–sea gas exchange was reduced. This shift from LGM deep-water formation in the region south of the ACC to Holocene bottom water formation in the southwestern Weddell Sea, can explain lower preformed δ 13C DIC values of glacial circumantarctic deep water of approximately 0.3‰ to 0.4‰. Our reconstruction brings Atlantic and Southern Ocean δ 13C and Cd/Ca data into better agreement, but is in conflict, however, with a scenario of an essentially unchanged thermohaline deep circulation on a global scale. Benthic δ 18O-derived LGM bottom water temperatures, by 1.9°C and 0.3°C lower than during the LH at deepest southern and shallowest northern sites, respectively, agree with the here proposed reconstruction of deep-water circulation in the eastern South Atlantic Ocean.