Environmental Controls on the Geochemistry of a Short-Lived Bivalve in Southeastern Australian Estuaries

Abstract

Geochemical signals in bivalve carbonate hold the potential to record environmental change over timescales from months to centuries; however, not all bivalves provide reliable proxy records, and modern studies are essential to calibrate these relationships prior to use in palaeo-environmental reconstruction. In this study, 19 shells of the estuarine bivalve Arthritica helmsi, from 14 sites in Southeastern Australia, were obtained from museum collections and analysed for trace elemental (Sr/Ca, Mg/Ca, Sr/Li and Ba/Ca) and stable isotopic ratios (18O/16O and 13C/12C). Mean Sr/Ca and Mg/Ca exhibited significant negative correlations to temperature (R2 = 0.49, p = 0.001; R2 = 0.25, p = 0.02) in agreement with previously published models for trace element partitioning into inorganic aragonite. In addition, the within-shell range of Sr/Ca and Mg/Ca, as measured by laser ablation ICP-MS, correlated to the temperature range (R2 = 0.22, p = 0.03; R2 = 0.46, p = 0.002, respectively). Sr/Li ratios were also negatively correlated to temperature (R2 = 0.34, p = 0.008); however, a significant difference in the model coefficients with previous studies indicates this proxy should be applied with caution. Both oxygen and carbon isotope values exhibited large differences between shells from terrestrial, estuarine and marine waters, suggesting that these stable isotopes hold a potential to record large environmental changes such as sea-level changes or freshening/salinisation in estuarine environments. This study presents the first geochemical study of Arthritica helmsi, highlighting its potential as an environmental tracer.