7000 years of dust deposition: A proxy record of alpine drought and climate variability in the Snowy Mountains, Australia

Blowing dust is symptomatic of drought in eastern Australia and accordingly dust deposits provide a unique proxy of climate variability and drought in this region. In this paper we present a high resolution (decadal scale) 7000 year record of alpine drought constructed from the analysis of peat cores collected from ombrothrophic mires in the headwaters of the Snowy Hydro Scheme catchments in Australia's Southern Alps. Dust was recovered from the cores by high temperature combustion and age control was by ¹⁴C and ²¹⁰Pb dating methods. The chemistry of each dust sample was established using Inductively Coupled Mass Spectrometry (ICPMS) and then compared to an extensive database of potential dust source area chemistries to locate provenance.

Results show that trends in dust contents in the cores are in good agreement with existing palaeo-climate records for eastern Australia. They indicate increased aridity and climate variability in southern Australia over the past 5000 yrs with the catchments of the Scheme becoming increasingly drought prone over the past 3000 yrs. Spectral analysis of the dust flux record identified 30 to 60 year and 2 to 5 year cycles between periods of high and low dust deposition. Similar length cycles were found in the historical inflow records to the Scheme's alpine catchments (1905-2003). We infer these results to show that precipitation in the Scheme's alpine catchments is influenced by multi-year and multi-decadal climate oscillations linked to the El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) teleconnections, and their influence on regional circulation patterns over southeastern Australia. Importantly, results indicate that the most severe droughts in the alpine headwaters of the Snowy Hydro Scheme catchments may occur during El Niño events experienced in the last decade of the warm phase of the PDO. These results highlight the potential of this novel approach to reconstructing alpine drought histories, particularly for sites where historical instrument records are short or not available and proxy climate archives such as varves and tree ring records are not preserved.