THE SEDIMENTARY REGIME BENEATH THE DEEP WESTERN BOUNDARY CURRENT INFLOW TO THE SOUTHWEST PACIFIC-OCEAN

A review of hydrographic sections, single-channel seismic profiles, bo ttom photographs, and nephelometer profiles collected by the U.S.N.S. Eltanin, plus new seismic and sedimentary data from the R.V. Rapuhia, provide an insight into the sedimentary regime beneath the Pacific dee p western boundary current (DWBC),where it enters the SW Pacific off s outhernmost New Zealand at Macquarie Ridge and Campbell Plateau, There the DWBC is reinforced by the Antarctic Circumpolar Current (ACC) lar gely through the generation of deep-reaching eddies formed by interact ion of the ACC with the pronounced bathymetry. It is therefore a regio n of high eddy kinetic energy, which induces widespread abyssal erosio n, It is also where the DWBC receives its first major injection of ter rigenous sediment, which is transferred from southern New Zealand alon g the 450+ km-long Solander Channel, From Macquarie Ridge the ACC-DWBC travels northeast onto the Subantarctic Slope of Campbell Plateau, Th is high, steep, western boundary intensifies the how, causing erosion along the slope base, East of the scour the 800 km-long Campbell Drift has been deposited, This drift extends to 51 degrees S, where the ACC swings east to continue its circum-Antarctic journey, while the DWBC continues northeast to Bounty Trough, where the combination of abundan t sediment supplied by Bounty Channel, a subdued western boundary, and a less energetic DWBC, have allowed the Bounty Fan to form directly a cross the current path, Apart from localized winnowing near zones of h igh relief, evidence for widespread DWBC influence on the fan is incon clusive, However, current effects become more apparent north of Bounty Fan, where the steep western boundary resumes in the form of Chatham Rise, Eroded fan sediments have contributed to a series of small drift s at 4400-5000 m depth, whereas at 2400-3400 m depth on the flank of C hatham Rise, the DWBC has molded a sinuous terrace-like drift. Viewed regionally, sedimentation beneath the boundary current south of Chatha m Rise contrasts strongly with the regime to the north, The southern c urrent is energetic and terrigenous supply is intermittent, being rest ricted to glacial lowstands, Consequently, erosion is common, and drif ts are few and are themselves subject to erosion, By comparison, the c urrent north of the rise is generally slower and has a more consistent terrigenous supply, particularly near Hikurangi Channel, which has be en active irrespective of sea level, Thus widespread drift deposition is favored.