Controls Over Oxygen Isotope Fractionation in the Waters and Bivalves ( <i>Arthritica helmsi</i> ) of an Estuarine Lagoon System

Oxygen isotope ratios in bivalve shells have long been used as a proxy for environmental change, reflecting both temperature and the oxygen composition of host water. In estuarine systems, water is complicated by variable mixing between river seawater, well evaporative enrichment. addition, due to species-specific variation temperature-dependent fractionation into carbonate, modern calibrations are necessary prior applications paleoenvironmental studies. this study, live specimens micromollusc Arthritica helmsi were collected from five sites Coorong Lagoon, an system at mouth River Murray, Australia, on six occasions November 2016 May 2018. Whole shell carbon compositions (n = 131) measured alongside monthly hydrogen analyses waters neighboring Lake Alexandrina 137). mostly controlled evaporation source waters, though period high discharge was reflected isotopic values North Lagoon. A equation calibrated A. helmsi: T (°C) (21.39 ± 0.45) ? (4.43 0.38) × (?18Oshell ?18Owater). This similar other published paleotemperature equations biogenic carbonates. These contemporary observations hydrology Coorong, coupled with our calibration fractionation, lay foundation studies using bivalves sediments Coorong.