The late Quaternary filling of Lake George, Australia: evidence from the Winderadeen Embankment

<p dir="ltr">Lake George is the largest endorheic lake of eastern New South Wales, often thought of as the benchmark for southeastern Australia palaeoclimate reconstructions. Abandoned shoreline features surrounding the lake, show a history of lake level fluctuations and climate variability during the late Quaternary. To address the ongoing discussion of a wet versus arid Last Glacial Maximum (LGM), this study aims to revisit the classic Lake George palaeoclimate work of Coventry (1976), applying updated coring and dating techniques to create a more reliable depositional history of the largest abandoned shoreline feature, the Winderadeen Embankment. It is hypothesised that the embankment was deposited prior to the LGM, and therefore previous water balance studies may have provided unreliable estimates for precipitation predictions during the LGM.</p><p dir="ltr">Two deep cores (LGWS1 = 19.3 m and LGWS2 = 14.4 m) were collected from the Winderadeen Embankment; a site of previous sedimentary investigations. Three dominant lacustrine facies units were identified: coarse- grained beach facies (sand and gravel), near shore facies (muddy gravel) and deep water facies (silt and clay). Twenty samples were chosen from each core to undergo a particle size analysis, and a total of five single-grain optically stimulated luminescence (OSL) samples were analysed as part of a broader project on Lake George. The results indicate that the bulk of the embankment was deposited from 43 to 58 ka, during Marine Isotope Stage (MIS) 3. The stratigraphy of the embankment suggests that the water level fluctuated between a maximum depth of 30 m and a minimum depth of 18 m during this time. Subsequently, the lake experienced an overall regression, with an estimated average depth of around 11 meters during the LGM. The updated water balance analysis, using simple water balance equations, suggests that this depth could be maintained during the LGM with less than half the modern mean precipitation. It was also shown that a depth of 11 m could be produced in modern times with a 18% decrease in annual evaporation or a 21% increase in precipitation or 17 years of a continuous La Niña.</p><p dir="ltr">The palaeoenvironmental record shows a history of fluctuating climates and water levels during the late Quaternary, with the highest lake levels during MIS3. Although the LGM experienced exceptional depths, they were significantly lower than those in MIS3. The study suggests that southeastern Australia maintained a positive moisture balance during the LGM despite reduced precipitation, contributing significantly to the ongoing discussion of the region's climatic conditions during the late Quaternary. The implication of this research underscores the need for further investigation into the timing of lake level fluctuations during the deposition of the Winderadeen Embankment and to perform a sensitivity analysis of the water balance results.</p>