Glacial-Holocene Paleoproductivity off Western Australia: A Comparison of Proxy Records

We compare paleoproductivity proxy records from a set of gravity cores from the Exmouth Plateau (≈ 19°S, 113°E, 950 to 2250 m) and the Perth Basin (≈ 27°S, 111°E, 2750 m) in the southeastern Indian Ocean. In general, these proxies indicate higher surfaceocean productivity in this region at the Last Glacial Maximum (LGM, isotope Stage 2). LGM sediment accumulation rates and the accumulation rates of biogenic sediment components (CaCO₃ and organic carbon) are a factor of 1.5 to 2 higher than Holocene values. Benthic foraminiferal abundances and accumulation rates are both higher in glacial sediments, as are the concentrations and accumulation rates of authigenic uranium in the sediments. These benthic foraminiferal abundance and authigenic uranium data suggest higher surface ocean productivity during the glacial, but we cannot yet relate them to carbon flux quantitatively. In contrast to these three approaches, a productivity proxy based on paired-species benthic foraminiferal δ13C differences shows little glacial-Holocene change. Possible explanations for this disagreement are discussed.Together, the data suggest that the glacial productivity off Western Australia was elevated relative to Holocene values, and support the hypothesis that a north-flowing west Australian current led to coastal upwelling and enhanced primary productivity off western Australia during the Last Glacial Maximum. However, glacial productivity was high only relative to the low productivity characteristic of this region in the modern ocean. We see no evidence of strong upwelling similar to that observed in the modern ocean off the southwestern coasts of Africa and South America.