Reconstructing deglacial and Holocene climatic and environmental change in the Snowy Mountains of southeast Australia

Multi-proxy, long-term records of deglacial and Holocene climatic and environmental change in southeast Australia are rare, leaving the region a gap in local and large-scale synoptic climate reconstructions. The Snowy Mountains include the highest and coldest regions of mainland Australia and were the only part of the mainland that was glaciated during the late Pleistocene. Lakes formed by the glaciers have provided continuous sediment traps since glacial retreat following the Last Glacial Maximum. In this report, I reconstruct the maximum ice extents of glaciers during the last glacial period and estimate their equilibrium line altitudes, revising the work of Barrows et al. (2001) using recently published 2-m resolution lidar imagery. My remapping changes the extents of two out of the eleven identified glaciers and expands the total glaciated surface area to ~16 km2, a 9% increase from that of Barrows et al. (2001). I also construct an 18.2 kyr record of environmental change based on analyses of an 8.2 m sediment core from Blue Lake, the largest and deepest of the lakes in the Snowy Mountains. This record incorporates several proxies, including loss-on-ignition, magnetic susceptibility, laser grain size analysis, and several ratios derived from Xray fluorescence scans that serve as proxies for physical and chemical weathering in the catchment and as complementary measures of grain size and grain size variability. The Blue Lake record suggests that the environment was highly variable immediately following deglaciation. The Snowy Mountains experienced a cold and/or dry climate between 18.1 - 16.7 thousand calibrated years before present (cal ky BP) followed by warm and/or wet conditions between 16.7 - 16.3 cal ky BP, a return to cold and/or dry conditions from 16.3 - 15.8 cal ky BP, and a brief climate amelioration with relatively warm and/or wet conditions between 15.8 - 14.9 cal ky BP. A major shift between 14.9 - 12.6 cal ky BP reflects a largely devegetated landscape reflecting cool and/or dry climatic conditions that appears to coincide with the Antarctic Cold Reversal, a cold period identified in much of the Southern Hemisphere south of 40 ºS. There is evidence for relatively warm and/or wet conditions during the period encompassing the Younger Dryas and earliest portions of the Holocene (12.6 - 10.8 cal ky BP). A clastic-rich interval dated to 10.8 - 9.7 cal ky BP suggests a final possible episode of cool and/or dry conditions in the early Holocene, but such an event has not been recognized elsewhere in Australia or the Southern Hemisphere. After ca. 9.7 cal ky BP, conditions appear to shift permanently to relatively stable, near-modern (relatively warm/wet) values overall, although there is evidence for possible cooling and/or drying coincident with the 8.2 ka event, as well as minor possible cooling/drying or increased fire impacts during an interval between 2.2 - 1.2 cal ky BP. Overall, the Blue Lake climate record bears more similarities to those of high Southern latitudes than to those in northern or tropical latitudes over the last 18.2 kyr, suggesting that southeast Australia's climate is synoptically tied to that of Antarctica, New Zealand, and Patagonia. Future work in the Snowy Mountains should focus on obtaining quantitative temperature and precipitation records throughout the whole deglacial and Holocene periods from all the glacial lakes to improve upon this record and identify catchment-specific effects.