Unravelling the Winds of the Past: Atmospheric Drivers of Beach Ridge Formation in Kati Thanda-Lake Eyre, Australia

Paleolake beach ridges, formed by wave-piled sediment, are exceptional markers of ancient lake-stands, providing critical proxies for paleohydrology. In dryland environments, where water is presently scarce and lakes are predominantly shallow and ephemeral, these proxies offer evidence of past wetter periods and potential insights into future hydrological scenarios. However, the atmospheric conditions responsible for the wind- and wave-storms that create beach ridges in shallow lakes remain uncertain. To investigate these conditions, we analysed the largest desert lake in the world, Kati Thanda-Lake Eyre (KT-LE) in Australia. We explored the factors behind ridge formation by combining wave modelling simulations driven by atmospheric reanalysis data with optically stimulated luminescence (OSL) dating of the lake’s historical shorelines. Our analysis focused on 12 of the most intense wind- and wave-storms, selected from a dataset of over 1,000 identified windstorms recorded between 1950 and 2023. We found that significant lake waves are predominantly generated by a synoptic dipole pattern, characterised by a high-pressure gradient between a cyclone and an anticyclone over southern Australia, often amplified by the passage of an atmospheric front. This pattern produces high-magnitude (>10 m s^-1) southerly winds, driving waves that can exceed 0.75 m in significant wave height. Despite these findings, wave simulations based on historical water depth observations suggest that no single storm was likely responsible for the formation of KT-LE's modern beach ridge. This conclusion is further supported by OSL dating and high-resolution topographic analyses, showing composite barrier landforms with regressional features. The OSL chronology indicates that some sections of the modern barrier or paleo-shoreline are effectively “modern,” as evidenced by their very low residual OSL signal, while other locations preserve beach deposits that are centuries old. These findings suggest that the formation of the modern shoreline is most likely the result of cumulative sediment deposition over multiple windstorms, rather than a single large storm event. While the precise mechanisms behind the construction of such shorelines during the late-Pleistocene and Holocene remain uncertain, our study identifies potential atmospheric conditions involved and highlights the processes shaping desert lake systems.