Glacial-interglacial changes in Subantarctic sea surface temperature and δ18O-water using foraminiferal Mg

Laboratory culturing experiments with living Globigerina bulloides indicate that Mg/Ca is primarily a function of seawater temperature and suggest that Mg/Ca of fossil specimens is an effective paleotemperature proxy. Using culturing results and a core-top Neogloboquadrina pachyderma calibration, we have estimated glacial-interglacial changes in sea surface temperature (SST) using planktonic Mg/Ca records from core RC11-120 in the Subantarctic Indian Ocean (43 degrees S, 80 degrees E) and core E11-2 in the Subantarctic Pacific Ocean (56 degrees S, 115 degrees W). Our results suggest that glacial SST was about 4 degrees C cooler in the Subantarctic Indian Ocean and 2.5 degrees C cooler in the Subantarctic Pacific. Comparison of SST and planktonic delta(18)O records indicates that changes in SST lead changes in delta(18)O by on average 1-3 kyr. The glacial-interglacial temperature change indicated by the Subantarctic Mg/Ca records suggests that temperature accounts for 40-60% of the foraminiferal delta(18)O change. We have used the Mg/Ca-based SST estimates and delta(18)O determinations to generate site-specific seawater delta(18)O records, which suggest that seawater delta(18)O was on average 1 parts per thousand more positive during glacial episodes compared with interglacial episodes. (C) 1999 Elsevier Science B.V. All rights reserved.