SOLITARY, AZOOXANTHELLATE SCLERACTINIAN CORALS FOR QUATERNARY RECONSTRUCTIONS OF THE INDONESIAN THROUGHFLOW, LEEUWIN CURRENT, AND PALEOENVIRONMENTS ON AUSTRALIA’S NORTHWEST SHELF

The Indonesian Throughflow (ITF) transports warm water from the Indo-Pacific Warm Pool to the Indian Ocean, influences the thermohaline conveyor circulation and global climate, and drives the Leeuwin Current – a warm, low-salinity, nutrient-deficient, southerly-flowing current along Australia’s Northwest Shelf (NWS). Prior studies suggest strength and extent of the Leeuwin Current varied over the Quaternary, but increased ~1 Ma, facilitating expansion of tropical marine biota along Western Australia. To obtain a detailed history of the ITF and Leeuwin Current, International Ocean Discovery Program (IODP) Expedition 356 drilled sediments at 7 NWS sites spanning 29°–18° S. In situ solitary azooxanthellate scleractinian corals from these cores will be combined with other biostratigraphic and sedimentologic evidence (e.g. D¹⁸O, D¹³C, U, K, Th, sediment grain size, foraminiferal abundances) to reconstruct paleoenvironments on the NWS. A total of 183 fossil corals, with estimated ages of <1.6 – 0.29 Ma, have been recovered. They are now being identified, their temporal and spatial distributions determined, and ecological settings inferred from literature and (paleo)ecological databases. Selected corals will be isotopically dated to refine age models. The 100 specimens identified to lowest possible taxonomic level represent 21 species, 17 genera, and 5 families. They include new Western Australian records for 1 genus and 11 species, the first fossil occurrences of 1 genus and 14 species, and 1 newly described species. Of 9 species previously known from Western Australia, 7 are considered tropical taxa and 2 temperate taxa. To date, only 18 fossil azooxanthellate coral specimens (Late Cretaceous – Late Pleistocene) have been reported for Western Australia. This new collection thereby increases the number of fossil specimens in the region by 10 times. In addition to providing new insights to the history of the ITF and Leeuwin Current, this collection expands understanding of the global and temporal diversity of solitary corals and highlights the challenges and necessity of studying deep-water organisms and ecosystems.