Texas A&M University, United States

Benthic stable isotopic measurements from four ODP Leg 189 sites, in and near the Tasmanian Gateway, link existing southern high latitude records from the Oligocene. Bulk sediment isotopic analyses at Sites 1170-1172 present the first moderate resolution, high latitude "planktic" late Oligocene to early Miocene data. Stable isotopes and records of carbonate content suggest similar surface hydrography for southern Sites 1170-1171, and strongly reduced offsets at Site 1172 to the north. Greater offsets of 1170-1172 benthic (super 18) O from southern Kerguelen Plateau values, continuing until 25.4 Ma, cast doubt on hypotheses of earlier development of circum-Antarctic circulation and therefore deep opening of the Drake Passage. The data also suggest that Southern Hemisphere temperatures in this area were relatively warm throughout the late Oligocene, consistent with published Mg/Ca temperature reconstructions for bottom waters. (modif. j. abstr.)