ODP Leg 181 targeted drill sites located in the eastern New Zealand region and the key southwest Pacific gateway because:
1. The Pacific DWBC is today one of the largest single contributors to the deep waters of the world's oceans, and, therefore, deciphering its history is of fundamental importance to global ocean paleohydrography.
2. The stratigraphic record of the eastern New Zealand Plateau and its abyssal margins is the best available for deciphering the history of development of Pacific Southern Ocean water masses and of the sediment drifts that they deposited.
3. The gateway region includes two major oceanic fronts, the Subtropical Convergence and the Subantarctic Front (Fig. 1). Thus, the region is in a prime position to allow determination of the migration of these boundaries, the forcing processes that cause them to move, and the environmental response to their movement.
4. The stratigraphic record from ENZOSS is of interest in its own right, as a major geological and sedimentary system within which sources, sinks, and material fluxes can all be quantified. The ENZOSS record is also directly relevant to one of the most important unresolved problems of Cenozoic climatology, namely the timing and precise nature of the development of widespread glaciation on the Antarctic continent (e.g., Barrett, 1996). In turn, it is, of course, these same glacial events that contribute source water to the DWBC and its companion flow, the ACC, which forces the boundary current south of 49°S.
The Leg 181 drilling schedule included 51 days at sea with drilling operations at seven sites. We began by drilling shallow-water sediment drifts on the upper continental slope near South Island New Zealand, moved south in difficult weather conditions to drill sites on the central Campbell Plateau, and, at its eastern foot, turned north to drill a deep hole through the levee sediments of the Bounty Fan, and finished by drilling two holes through sediment drifts on the north side of the Chatham Rise, and one into the shallow rise itself. Overall, we recovered 3600 m of core, and made over a million shipboard measurements. The material collected on Leg 181 will lead to a better understanding of the history and evolution of the Pacific ACC-DWBC system and related oceanic fronts and to the important role they play in global ocean circulation. Finally, that the stratigraphic and paleontologic information retrieved on the cruise contained many surprises was itself predictable, given the paucity of previous drilling in the Southwest Pacific area. This information will provide a vital database for the targeting of future drilling legs in the Southern Ocean.
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