Late Quaternary Paleoceanographic And Paleoclimatic Changes in the Tasmanian Seaway (ODP Leg 189)

The Tasmanian Gateway, focussed on during ODP-Leg 189, is an oceanographic key area within the Southern Ocean (Power-House-Ocean). Our investigations focus on the last approximately 500.000 years of sedimentation at sites 1168 (western Tasmania margin), 1170 and 1171 (Tasman Rise), and 1172 (East Tasman Plateau). We established age models for sites 1168, 1170, and 1172 by applying benthic oxygen isotope stratigraphy. The stratigraphy of site 1171 was established by correlating the high resolution reflectivity record to the other cores. Inferred sedimentation rates are around 1-4 cm/kyr during most of the time. Nannofossil oozes with an important foraminiferal component dominate the sedimentation. Carbonate concentrations range from 70-98%, with lowest concentrations at sites close to Tasmania. The temporal variability of the carbonate sand fraction indicative of changes in carbonate preservation/dissolution shows clear differences east and west of Tasmania, pointing to temporal and spatial changes in lysocline depths at the interface between Pacific and Indian oceans. The flux of terrigenous matter (indicated by magnetic susceptibility, concentrations of siliciclastics, aluminum, iron and titanium concentrations) is very low, but regionally different. Close to Tasmania, the supply of terrigenous material is highest. Eolian transport apparently serves as the prime source for terrigenous matter, since i) Fe/Al ratios of 0.3 are close to dust values, ii) iron, titanium and aluminum accumulation rates match the Vostok dust record, and iii) the glacial/interglacial magnitudes of iron accumulation rates in the sediment records correspond to eolian iron fluxes. Marine productivity (assessed from calcium carbonate, biogenic barium, and chlorins) is reflecting the glacial/interglacial change in the strength of the subtropical East Australian Current. During glacials, the waning influence of the oligotrophic East Australian Current allows the intrusion of nutrient-rich subantarctic waters, and thus the northward propagation of the Subtropical Convergence.