Isotope rates and Cd/Ca ratios in benthic foraminifera from the Southern Ocean

South Atlantic benthic foraminiferal Cd/Ca shows no glacial-interglacial variation, suggesting that the glacial contribution of North Atlantic Deep Water to the Southern Ocean was not much different than at present. In contrast, Cd/Ca in southeast Indian Ridge cores show lower glacial bottom water Cd, comparable to levels in intermediate depths of the North Atlantic and significantly lower than in the deep South Atlantic. Low glacial Cd/Ca was also recorded in planktonic foraminifera, suggesting a substantial decrease in the nutrient concentration of Subantarctic surface water during the glacial maximum which most likely was caused by increased biological productivity. The Cd data are inconsistent with low glacial benthic foraminiferal d13C which suggest higher nutrient concentration. We propose that the low Cd/Ca in the Southeast Indian Ridge records reflects a local source of nutrient-depleted deepwater, formed during the last glacial maximum by open-ocean convection near the Antarctic Polar Front, downstream of the Kerguelene Plateau. If this source was limited to the southeast Indian basin then its impact on the overall chemistry of glacial Circumpolar Deepwater was rather small. However, if during glaciations open-ocean convection became the dominant mode of bottom water formation, it might have had a greater impact on CPDW chemistry