A high-resolution record of south-eastern Australian hydroclimate between 30,000 - 10,000 years ago: toward a better understanding of the Australian LGM

Global climate variability during the late Quaternary is commonly framed in terms of the ‘bipolar seesaw’ pattern of asynchronous temperature variations in the northern and southern polar latitudes. However, the terrestrial hydrological response to this pattern in south-eastern Australia is not fully understood, as continuous, high-resolution, well-dated proxy records for the hydrological cycle in the region are sparse. Here we present a well-dated, highly resolved record of moisture balance spanning 30000 – 10000 calendar years before present (30 – 10 ka BP), based on x-ray fluorescence and organic carbon isotope (δ13COM) measurements of a sedimentary sequence from Lake Surprise in south-eastern Australia. The data provide a locally coherent record of the hydrological cycle (Fig. 2). Elevated Si (reflecting windblown quartz and clays), and relatively high δ13COM, indicate an extended period of relative aridity between 28 – 17.5 ka BP, interrupted by millennial-scale episodes of decreased Si and δ13COM, suggesting increased moisture balance. Peak aridity was reached between 21 and 17.5 ka BP, possibly representing the expression of the global Last Glacial Maximum. This was followed by a rapid deglacial shift to low Si and δ13COM at 17.5 ka BP, indicative of wetter conditions. We find that these changes are broadly coeval with similarly high-resolution records from south-eastern Australia and New Zealand. We also supplement our high-resolution record with discrete clumped isotope measurements on freshwater gastropods from Blanche Cave, also in south-eastern Australia. Temperatures either side of the Last Glacial Maximum were slightly cooler than those of the modern day, with the hint of a decrease from 40 to 30 ka BP. We did not find gastropods within the 28-17.5 ka BP interval in this cave, but identify this as a period for urgent attention. Together, our analyses suggest that drivers of the regional hydrological cycle have varied on multi-millennial time scales, in response to major shifts in global atmosphere-ocean dynamics during the last glacial-interglacial transition. Southern Ocean processes were the dominant control on hydroclimate during glacial times, via a strong influence of cold sea surface temperatures on moisture uptake and delivery onshore. Following the last deglaciation, the southward migration of cold Southern Ocean fronts likely resulted in the establishment of conditions more like those of the present day. These conclusions will be tested in future work, focused on quantitative rainfall estimates from clumped isotope of land snail shells. Figure 1. Selected data from the Lake Surprise record: a) Bulk sediment carbon isotope ratios (δ13COM), interpreted to reflect plant moisture stress; b) First principal component (PC1) of the calibrated scanning XRF dataset, interpreted to reflect aeolian deposition of Si. Arrows indicate periods of increased effective moisture within the relatively arid LGM. Triangles denote 14C age control points.

Keywords

Australia, Quaternary period, Quartz, Clays, X-ray fluoresence analysis, Data, Carbon isotopes, Organic matter

Citation

Falster, G., Tyler, J., Grant, K., Tibby, J., Turney, C., Löhr, S., Jacobsen, G., Kershaw, A. P., Kluge, T., Drysdale, R., & Dux, F. (2019). A high-resolution record of south-eastern Australian hydroclimate between 30,000 - 10,000 years ago: toward a better understanding of the Australian LGM. Paper presented to the 20th INQUA Congress, 25th - 31st July 2019, Dublin, Ireland. Retrieved from: https://virtual.oxfordabstracts.com/#/event/public/574/submission/56