Glacial/interglacial variations of sedimentation on the West Australian continental margin: constraints from excess 230 Th

Abstract

Abstract We determined the mass accumulation rates of biogenic (carbonate, organic carbon, Ba) and terrigenous (Al, Th) sediment components, together with excess 230 Th in gravity cores from the Exmouth Plateau and the Perth Basin on the West Australian continental margin, in order to reconstruct paleoceanography and paleoclimate in this critical area during the Late Quaternary. We found the mass accumulation rates of these components, based on normalization to age-corrected initial excess 230 Th in the sediments (constant flux model), to be more reliable for this purpose than the site-specific burial rates, since the latter appear to be affected by lateral sediment redistribution from the shelf and slope. Under the constraints provided by the constant 230 Th flux model, there is little convincing support for enhanced productivity off Western Australia during the last glacial maximum and hence no compelling evidence in the sediment record for strong coastal upwelling comparable to that in the modern ocean off the west coasts of Africa and South America. The hypothesis of a major reorganization of ocean circulation in the southeastern Indian Ocean involving the replacement of the south flowing Leeuwin Current with the north flowing West Australian Current during the last glacial maximum should therefore be viewed with reservations. The flux pattern of Al and Th indicates a significantly lower input of terrigenous components during the last glacial maximum than during the Holocene, suggesting that the supply of terrigenous components to the deep sea floor in this area have been influenced primarily by variable runoff from monsoon-controlled northwestern Australia. The results are consistent with expanded aridity during glacial times and a somewhat wetter climate in NW Australia during interglacials.