The use of ostracoda in the palaeoenvironmental reconstruction of the Gulf of Carpentaria, Australia, from the last interglacial to present

Throughout the majority of the last glacial cycle, the Gulf of Carpentaria, the large body of seawater that extends as a broad tongue into the north of Australia, was an enclosed lake. It would have been possible to walk around the perimeter of the lake from Australia to New Guinea. Aboriginal oral tradition recalls that during some periods, the lake teamed with freshwater fish and waterfowl. At other times, it was shallow and segmented into a series of saline swamps and pools, or even dry and subaerially exposed. Marine waters transgressed the lake margins during periods of high sea level, forming a shallow marine embayment through to open marine conditions. A large brackish lake remained as the waters again receded. The present open shallow marine conditions were emplaced within the last eight thousand years. Fluctuations in the extent and nature of this waterbody through the last glacial cycle are preserved in the sediments of the gulf. The sedimentological interpretation of core material retrieved from the gulf provides a framework of palaeoenvironmental change in the region, in particular the extent of the lake basin, timing of marine influence and evidence of channel activity. Through the detailed analysis of ostracod faunal assemblages of the core sediment and comparison with modern species distribution, inferences are drawn about the ecology of the gulf basin at the time of valve formation. Morphological variation and preservation of the valves also provide information regarding the changing conditions of the waterbody and post-depositional effects. The geochemistry of the ostracod valves permits insight to variations in climate, particularly temperature and effective precipitation change. Comparison and correlation are made with the global sea-level curve and regional climatic records. The implications for the range of environments evident in the gulf region through this period include the presence of warm shallow water for latent heat transport and the generation of cyclones, strengthened monsoon conditions and the mixing of Indian and Pacific Ocean waters through Torres Strait at high sea-level times, and greater continentality, reduced rainfall and altered oceanic currents during sea-level lowstands. The impact of the changing conditions, and shorelines, would have been particularly significant for the human inhabitants who have been present in this region for at least the last fifty thousand years. The nature and extent of the waterbody through the period has enormous implications for people, both as a resource for food and a potential land-bridge between Australia and New Guinea