No 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

Leg 184 will core hemipelagic sediments in the South China Sea (SCS) to determine the evolution and variability of the East Asian monsoon in the late Cenozoic. Of the six proposed drill sites (Fig. 1), five are located on the northeastern continental slope southeast of the Dongsha Islands, and one is on the southern slope south of the Nansha Islands near the Sunda Shelf, with water depths ranging from 625 m to 3190 m. The main goal of Leg 184 is to improve our knowledge of the link between climate and tectonics. Land-based studies in China and other parts of East Asia have developed a four-stage model of monsoon evolution. The proposed drilling will calibrate the terrestrial record with that of the global ocean. It is suggested that uplift of the Tibetan Plateau is responsible for both the late Cenozoic global cooling and for the intensification of the Asian monsoon; therefore, a comparison between records of monsoons, denudation rates, and climate cooling in the SCS will test this hypothesis. Drilling of high-sedimentation-rate hemipelagic deposits in the SCS will provide the proxy records for this test. There are four major scientific objectives for the leg: (1) to obtain a continuous marine record of East Asian climate history for the late Cenozoic and to compare the evolution of the East Asian monsoon system with the South Asian or Indian monsoon system; (2) to examine the possible relationship between the Tibetan Plateau uplift, monsoon evolution, and global cooling; (3) to improve our understanding of the stability of the Western Pacific Warm Pool and the role of seasonality changes in low-latitude marginal seas; and (4) to establish a detailed history of sea-level changes for the SCS.