FY98 Science Program Summary

Abstract

Leg 177 will core sediments in the southeast Atlantic sector of the Southern Ocean to study the paleoceanographic history of the Antarctic region on short (millennial) to long (Cenozoic) time scales. Six primary sites are located along a latitudinal transect across the Antarctic Circumpolar Current (ACC) from 41° to 53°S, including two sites (TSO-6A/B, TSO-7C/B) within the circum-Antarctic siliceous belt. The sites are also arranged along a bathymetric transect ranging from 2100 to 4600 m water depths, intersecting all of the major deep and bottom water masses in the Southern Ocean. The general goals of Leg 177 are twofold: (1) to augment the biostratigraphic, biogeographic, and paleoceanographic history of the earlier Cenozoic, a period marked by the establishment of the Antarctic cryosphere and the ACC; and (2) to target expanded sections of late Neogene sediments that will resolve the timing of Southern Hemisphere climatic events on orbital and suborbital time scales, which can be compared with similar records from other ocean basins and with ice cores from Greenland and Antarctica. Drilling the proposed sites will provide the sedimentary sequences needed to address a number of first-order problems in southern highlatitude paleoclimatology and stratigraphy including (1) the evolution of the ACC and past changes in the position of the Polar Front Zone and the Antarctic sea-ice field; (2) the evolutionary history and stability of the Antarctic cryosphere; (3) changes in Southern Ocean productivity, nutrient cycling, and pCO 2 and their role in global biogeochemical cycles; (4) changes in the mixing ratio of various deep and bottom water masses in the Antarctic (e.g., North Atlantic Deep Water); (5) the response of the Southern Ocean to orbital forcing and the