Late Quaternary productivity changes from offshore Southeastern Australia: A biomarker approach

Abstract

Reconstructions of primary productivity at low latitudes have been the focus of several studies to better understand how the export of nutrient-rich, intermediate Southern Ocean (SO) waters influences productivity at these latitudes. This was triggered by the general observation of minima in the planktonic foraminiferal δ13C values during deglaciations, which was interpreted as an isotopic signal of intermediate SO waters, together with a concomitant increase in diatom productivity at some equatorial sites. However, the impact of these SO waters on productivity at higher latitudes is not well constrained. Here, we compare a high-resolution planktonic foraminiferal δ13C record with total organic carbon and biomarker records for Proboscia diatoms and haptophytes in marine sediments from offshore Southeastern Australia. The planktonic foraminiferal δ13C record shows distinct minima during deglaciations and the Marine Isotope Stage 4/3 transition, tentatively suggesting that13C-depleted SO waters reached the coast of Southeastern Australia. However, it did not result in increased productivity during these periods. Instead, the highest primary productivity period, as indicated by total organic carbon and alkenone accumulation rates, occurred during the Last Glacial Maximum while Proboscia diatoms mainly proliferated during interglacials and Marine Isotope Stage 3 matching periods of increased diatom productivity in some sites of the Eastern Equatorial Pacific. Our study suggests that increased primary productivity offshore Southeastern Australia was mainly due to stronger westerly winds during glacial periods while Proboscia diatom productivity was probably controlled by the transport of silicic acid to this area.