Quaternary Antarctic ice-sheet fluctuations and Southern Ocean palaeoceanography: natural variability studies at the Antarctic CRC

In its first three years, the Antarctic CRC s Natural Variability Program has focussed research effort on understanding changes in the extent of the East Antarctic ice sheet, the sedimentary processes and biogeochemical cycles affecting shelf sedimentation, and the palaeoceanography of the Southern Ocean. Seismic data from the Prydz trough-mouth fan indicate that it contains a high-resolution time series of the Plio-Pleistocene activity of the Lambert Glacier system. The fan has been prograding from the eastern side of Prydz Bay at least since the Miocene and it contains Plio-Pleistocene sediments, which are 0.8- 1.2 s TWT thick beneath the current shelf break. Radiocarbon dating of shelf sediments indicates that deposition of a Holocene siliceous mud and ooze layer was initiated at about 10 ka BP on the Mac. Robertson Shelf, which is interpreted as coinciding with the retreat of an expanded ice sheet from the shelf break. Geochemical analyses of sediment cores from the Mac. Robertson Shelf suggest significant differences in sediment accumulation between the inner and outer shelf during the Holocene. A core from the outer shelf suggests three episodes of intense diatom production separated by periods of around 1500 years, although long-term average sediment accumulation rates appear to be rather uniform for this location during the middle and late Holocene. In contrast, results for a core from the inner shelf suggest an approximately 7-fold increase in average sediment accumulation rate from the mid to late Holocene, with roughly comparable increases in the accumulation of both biogenic and lithogenic material. Palaeoceanographic studies of the Southern Ocean, using planktonic foraminifera, diatoms and alkenone unsaturation ratios, indicate larger sea surface temperature amplitudes over wider areas of the Southern Ocean during the last glacial maximum than previously suggested by CLIMAP. Our studies offer the possibility of improvements to reconstructed glacial boundary conditions, with wider areal coverage, greater reliability of estimates , and the opportunity for estimation of seasonal dynamics.