Yo-yo-ing of the Subtropical Convergence in Sympathy with the Vostok Climatic Record, 0-0.38 Ma: ODP Site 1119, Southwest Pacific Ocean

ODP site 1119 is located at water depth 395 m near the subtropical convergence, and just downslope from the shelf edge of eastern South Island, New Zealand. The site contains an expanded stratigraphic record of Southern Ocean Quaternary oceanographic change, the younger part of which correlates closely with the climatic history contained within the Vostok ice core. Four palaeoceanographic proxy measures vary in consonance with the main lithological glacial-interglacial cyclicity at the site. Interglacial intervals are characterised by high d13C and colour reflectance (a proxy for carbonate content), and low gamma-ray (a proxy for clay content) and d18O; conversely, glacial intervals exhibit low d13C and reflectance, and high gamma ray and d18O. Early interglacial intervals are represented by silty clays which enclose intervals of 10-65 cm thick, sharp-based, Chondrites-burrowed, shelly, graded, very fine sands. The sands are rich in foraminifers, including species of warm water affinities, and were deposited distant from the shoreline under the influence of longitudinal flow in relatively deep water, as the palaeo-STC passed shorewards across the upper slope. The enclosing glacial units, which comprise mostly micaceous silty clay, though with some thin (3-25 cm thick) sands present also at peak cold periods, contain the cold-water scallop Zygochlamys delicatula. The 1119 core records the seaward movement of the STC during glacial periods, accompanied by the incursion then of warmer subtropical water (STW) above the site, and landward movement during interglacials, resulting in a dominant influence then of colder subantarctic surface water (SAW). Intervals of thin, sharp-based, graded sands-muds occur within cold periods MIS 2-3, 6.2 and 7.4, and indicate the onset at times of peak cold of intermittent bottom currents which correspond to strengthened and expanded frontal flows along the STC, which at this time lay east of site 1119 in relatively close proximity to seaward-encroaching subantarctic waters within the Bounty gyre.