Abstract:
The introduction of the Ocean Conveyor concept in the mid 1980's provided a unified view of the world's oceanic circulation. Large thermohaline currents, density driven flows formed by differences in salt and heat, were found to interconnect the main oceanic basins. This system of currents conveys vast amounts of heat around the planet and hence has a profound influence on climate, ice sheets, and the marine environment. Offshore eastern New Zealand is a key region because it is the entrance or gateway for the Conveyor into the SW Pacific Ocean. Termed the SW Pacific Gateway, the eastern margin of Campbell Plateau and Chatham Rise steers the Conveyor northward as a deep western boundary current (DWBC) - so called because it flows along the western margin of the ocean basin. The gateway gains further distinction because: New Zealand generates large quantities of sediment that are reworked by the DWBC into sediment drifts thus providing an exceptional stratigraphic record of palaeoceanographic and palaeoclimatic change; the gateway encompasses a range of oceanic water masses and boundaries including the globe-encircling Subtropical Front and Subantarctic Front separating surface waters with subtropical to polar affinities; additional to the DWBC, the continental margin south of Chatham Rise is bathed by the Antarctic Circumpolar Current (ACC) which influences the Conveyor as well as strongly affecting regional oceanic and atmospheric climates. These and other features of the gateway attracted Leg 181 of the Ocean Drilling Program (ODP), and from August to October 1998, 7 sites were cored by the drillship Joides Resolution to recover 3.6 km of sediment (Fig 1). The following year the ODP initial reports summarizing shipboard data and observations were compiled and published. Preliminary interpretations were presented at a post-cruise workshop in February 2000. Now is the science publication phase. Individual contributions papers are beginning to appear in the international literature, a journal special issue devoted to Leg 181 is underway, and papers for the ODP scientific results volume have been submitted. As a preview of the forthcoming science from Leg 181, we present some stratigraphic and sedimentological highlights. These results are very much a team effort, but the names of the principle investigators have been included [in brackets] as contacts for further information.