Quaternary climatic instability in south-east Australia from a multi-proxy speleothem record

Milankovitch-scale Quaternary climatic oscillations within south-east Australia are known to be characterized by relatively arid glacial and wet interglacial stages. However, terrestrial proxy records of environmental change are scarce, based largely on river terraces, dune sediments and pollen sequences. Here we present a speleothem-based palaeoclimate record from Yarrangobilly caves, south-east Australia. The oxygen isotopic composition of calcite (δ¹⁸O_calcite) is taken to represent rainfall amount and used as an aridity index. High-resolution trace element profiles and UV fluorescence support interpretations based on δ¹⁸O_calcite, allowing further designation of key phases of speleothem growth into periods of relative aridity and moisture excess. A hiatus of approximately 37ka duration divides the record into two key phases of growth which can be mapped onto marine isotope stages 5c-a and 3, respectively. Increasing aridity in the latter half of MIS 5 led to cessation of speleothem growth for the duration of MIS 4. Growth recommences during MIS 3, associated with greater moisture availability, enhanced vegetation and augmented biogeochemical cycling. This speleothem record provides a unique context of terrestrial environmental change and depicts hydrological conditions which fluctuate markedly over the 70-ka period covering the time of megafauna extinction and human arrival on the continent.