SCIENTIFIC REPORT
ODP LEG 181 LEG SUMMARY:
SOUTHWEST PACIFIC GATEWAYS
INTRODUCTION
The circulation of cold, deep Antarctic Bottom Water (AABW) is one of the controlling factors in the Earth's heat budget and, ultimately, climate. Today, forty percent of the flux of cold bottom-water entering the major ocean basins does so through the Southwest Pacific Ocean, as a thermohaline Deep Western Boundary Current (DWBC) (Warren, 1981). The cold water in the DWBC is derived through dense waters sinking around Antarctica and through the entrainment and mixing of deep Atlantic and Indian ocean waters by the wind-driven Antarctic Circumpolar Current (ACC). At the approach to the Pacific Ocean, filaments of the ACC pass around and through gaps in the Macquarie Ridge to reunite further east and flow northeast along the eastern edge of the New Zealand microcontinent (Fig. 1A). Early in its journey, where it flows northeast along the edge of the Campbell Plateau, the DWBC is reinforced by the ACC. At the southern edge of the Bounty Trough (46°S), the ACC veers east and continues across the Pacific, whereas the DWBC flows on north at depths between ~4500 and 2000 m, across the Bounty Fan, around the eastern end of the Chatham Rise, northwestward across the northern boundary of the Hikurangi Plateau, to finally turn north and flow toward the equator along the Tonga-Kermadec Trench. Higher in the water column, north-spreading Antarctic Intermediate Water (AAIW), formed by subduction at the Antarctic Convergence (AAC), bathes the top and eastern upper flank of the Campbell Plateau in depths of 400–1500 m.