GLACIAL-INTERGLACIAL HISTORY OF ANTARCTIC INTERMEDIATE WATER - RELATIVE STRENGTHS OF ANTARCTIC VERSUS INDIAN-OCEAN SOURCES

Sediment cores from the southern continental margin of Australia are n ear the formation region of Antarctic Intermediate Water (AAIW) and Su bantarctic Mode Water and record the changes in these water masses fro m the last glacial maximum through the present. Carbon and oxygen isot opes were measured on the benthic foraminiferal species Planulina wuel lerstrorfi for both the Recent and last glacial maximum sections of th e cores and were then used to reconstruct temperature and carbon isoto pic water column profiles. The glacial oxygen isotope profile indicate s a vertical temperature structure for this region similar to that in today's Subantarctic Zone. Although intermediate water deltaC-13 canno t be used as a nutrient tracer in this region because of the large inf luence of air-sea carbon isotopic exchange on this water mass, deltaC- 13 can be used as a water mass tracer. Today, AAIW properties reflect contributions from cool, fresh Antarctic Surface Waters (2/3) and warm , salty waters from the Indian Ocean (1/3). When examined in conjuctio n with the glacial deltaC-13 and deltaO-18 data from the north Indian and Southern Oceans, our data suggest a much reduced contribution of N orth Indian Ocean intermediate water to glacial Antarctic Intermediate Water relative to the contribution of Antarctic Surface Water. This f resher, cooler glacial Antarctic Intermediate Water would be distribut ed to the intermediated-depth ocean, thus decreasing the transport of salt produced in the North Indian Ocean to the rest of the world's oce ans. Combined with evidence for a reduced influence of North Atlantic Deep Water, these results suggest major changes in the pathways for th e redistribution of heat and salt in the glacial ocean.