Controls on Late Quaternary sedimentation of the South Tasman Rise

The South Tasman Rise is a submarine continental plateau of about 1000-3000 m depth, in the Southern Ocean south of and separated from Tasmania by a saddle more than 3000 m deep. Its palaeoceanographic importance is that it lies between the subtropical convergence and the polar front and that latitudinal migration of these oceanographic features should be recorded in the calcareous oozes deposited on the rise. Late Quaternary sediment cores collected from the South Tasman Rise record climatically and current-controlled changes in sedimentation. Accelerator mass spectrometry C-14 dating of down-core variations in the carbonate concentration demonstrates that the core-top carbonate maxima are Holocene and down-core minima are successive glacial intervals. During glaciations the percentage of carbonate decreases, whereas the percentage of detrital minerals (terrestrial input) increases. The magnitude of climatically related signatures expressed in the sediments is a function both of proximity to terrestrial input from the north and of overlying water depth. Cores from the saddle separating the South Tasman Rise from Tasmania have large terrestrial input and high variations in carbonate concentration. Shallower water cores from the rise are consistently and strongly influenced by winnowing in both glacial and interglacial intervals, whereas deeper cores appear to be more influenced by carbonate dissolution during glaciations.