NEODYMIUM ISOTOPE EVIDENCE FOR COUPLED SOUTHERN OCEAN CIRCULATION AND ANTARCTIC CLIMATE THROUGHOUT THE LAST 120,000 YEARS

Here, we present Nd measurements made on uncleaned foraminifera from a sediment core, TT1811-34GGC, collected from the Southeast Indian Ridge in the Indian sector of the Southern Ocean (41.718°S, 80.163°W, 3167 m. water depth) in November 2018 as part of the CROCCA-2s coring expedition. Alongside sortable silt bottom water flow speed estimates, percentage CaCO₃ and benthic and planktic δ¹⁸O and δ¹³C measurements, our Nd isotope record of bottom water circulation suggests a tight coupling between Antarctic climate and Southern Ocean circulation throughout the last glacial cycle (Marine Isotope Stage [MIS] 5 to the Holocene). Our data suggest that the Southern Ocean responded rapidly to regional climatic changes during the inception of the last glacial period (MIS 5-4), leading changes in northern hemisphere climate. Shifts towards more radiogenic Nd isotope values and finer sortable silt fractions are interpreted as a reduction in the inflow of relatively well ventilated North Atlantic-sourced waters to the Southern Ocean at the expense of potentially more poorly ventilated, carbon-rich Pacific and Southern Ocean-sourced waters. This early shift increased the carbon inventory of the deep Southern Ocean and may account for some of the 40-80 ppm lowering of atmospheric pCO₂ observed during the late stages of MIS 5 (the last interglacial) and into MIS 2-4 (the last glacial period). Although changes in Southern Ocean paleocirculation have long been invoked to help account for peak glacial pCO2 values, out data suggest this may also have been an important factor in the imitation of glacial conditions during the MIS5/4 transition.