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Scientific Objectives

The primary objective of drilling at Site 1202 was to obtain a high-resolution record of the paleoceanographic history of the Kuroshio Currrent. Such a record might make it possible to identify long-term patterns of climate change associated with the western Pacific boundary current during the past 1.5 m.y. For example, the Kuroshio Current passes over the Ryukyu arc and into the Okinawa Trough before turning to the northeast and continuing toward Japan, but changes in sea level associated with glacial-interglacial cycles could well redirect the Kuroshio Current outside the arc and isolate the Okinawa Trough on a cyclical basis. Changes in sedimentation caused by such deflections, coupled with periodic exposure of the continental shelf to the northwest during low sea level stands, should be easily detectable by drilling at Site 1202.

We also hoped that drilling at Site 1202 would enable us to detect the effects of orbital forcing in the Pacific during the mid-Pleistocene (~0.7 Ma), when the Earth's climate system switched from a regime of dominant 41-k.y. cycles to 100-k.y. cycles. Oxygen isotope measurements on foraminifers from Site 1202, for example, should reflect surface temperature cycles over a large area of the western equatorial Pacific, because the Kuroshio Current is a composite current assembled from numerous smaller currents before it reaches the site.

We also hoped to document the temporal and spatial variability of millenial climate changes in the Kuroshio Current and the catchment basins that deliver sediments to the Okinawa Trough. These changes should be reflected not only in the oxygen isotopic composition of microfossils but in the grain size and composition of sediments from some of the largest river systems in east Asia, including the Yangtze, which rises in Tibet and samples much of southern China.

Finally, we hoped to examine long-term changes in El Niño/La Niña-style climate oscillations in the low-latitude Pacific by comparing the Kuroshio Current record to other Pacific ODP records (Andreasen and Ravelo, 1997; Clement et al., 1999).

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