Pleistocene variability of the Subtropical Convergence at East Tasman Plateau: Evidence from planktonic foraminiferal Mg/Ca (ODP Site 1172A)

Abstract

Combined measurements of Mg/Ca and stable oxygen isotopes in tests of the planktonic foraminifer G. bulloides from Ocean Drilling Program (ODP) Site 1172A (East Tasman Plateau) allowed us to reconstruct sea surface temperature (SSTMg/Ca), sea surface salinity (SSS), and hence variations in the Subtropical Convergence (STC) in the southwestern Tasman Sea over the last four major glacial‐interglacial changes. During interglacials the commonly enhanced SSTMg/Ca and SSS correspond to a lowered marine productivity and a lowered terrigenous flux, implying that the STC separating cool, high‐nutrient Subantarctic Surface Water from warm, saline, oligotrophic Subtropical Surface Water and hence the band of zonal westerlies responsible for the eolian dust flux were located south of East Tasman Plateau. The warm East Australian Current was well established during warm periods and propagated far south. During glacial times, SSTMg/Ca and SSS were lower, while both marine productivity and eolian flux increased. Such conditions prevailed during glacial Marine Isotope Stages MIS 12, MIS 10, and to a lesser degree MIS 6 and implied the extended northward influence of Subantarctic Surface Water and a shift of the STC to <44°S. The overall climatic signal at Site 1172A appears to be largely attenuated when compared to published climate records from comparable latitudes to the west and to the east. SSTMg/Ca amplitudes were more pronounced in the subantarctic Indian Ocean and at Chatham Rise. They exhibit a consistent pattern suggesting that latitudinal shifts of the STC occurred synchronously in the subantarctic Indian Ocean and at Chatham Rise but were largely damped at East Tasman Plateau due to the influence of the East Australian Current.