Lake carbonate geochemistry as a proxy for paleohydrology: a validation-in-time at West Basin Lake, Victoria

Abstract

There is a lack of extensive historical climate data in Australia, meaning high-resolution paleoclimate studies are essential for a more comprehensive understanding of natural climate variability. The majority of paleohydrology records in south-eastern Australia region are low resolution, millennial time-scale reconstructions, resulting in a lack of understanding of climate variability at shorter time-scales relevant to human life spans. Here, we attempt to validate the use of geochemical analysis of lake sediments from West Basin, Victoria, as a way to create a high resolution paleohydrology reconstruction. The isotopic composition of the lake water in West Basin is primarily controlled by the precipitation to evaporation ratio (P:E). Ostracod calcite and bulk inorganic carbonates (BIC) that form within the water column reflect these changes and thus are used as proxies of past changes in P:E. This reconstruction is supported by a 210Pb- and 240/230Pu-based chronology which estimates a sediment accumulation rate of 0.3 to 0.4 cm/year and a maximum age at 40 cm of 118 years. This enables the resulting oxygen and carbon profiles to be validated against instrumental records of annual rainfall and temperature. The oxygen profile exhibits good agreement with this climate record, with peaks in δ18O values often coinciding with periods of low annual rainfall. Based on this, the ostracod record was determined to be capable of recording reliable, high resolution changes in P:E. The BIC record, though less consistent, can produce a detailed profile where ostracods are unavailable. Studies of this kind are vital to improving the accuracy of proxy system models which allow for reconstructions to be extended further in the geological record. Such models would allow for contextual understanding of the severity of drought occurrences and the assessment of the possible impacts of human induced climate change.