Stable isotopic records of shell carbonate and the effects of ocean acidification along the Washington coast

In recent years stable isotope ratios of marine bivalve shells have received growing attention in fisheries research and management, especially for carbon isotopes (d13C) in detection of the effects of ocean acidification. Bivalve shells are composed of calcium carbonate (CaCO3) and exist in polymorphism as calcite and aragonite. When the anthropogenic CO2 sinks into ocean, it will produce HCO3- and CO32- and this affects the carbonate saturation state (Ω). In this study we report stable carbon and oxygen isotope analyses in shells of Pacific razor clam (Siliqua patula), Pacific geoduck (Panopea abrupta), and Pacific sea scallop (Patinopectin caurinus) along the Washington and British Columbia coast. Among 800 more powder samples analyzed the d13C values of these shells ranged from -2.88 to -0.30‰, whereas d18O values of the same samples ranged from -2.16 to +1.39‰. As compared with the carbon isotope signatures reported in the literature, data from this study did not show a steady decrease in d13C patterns. In contrast, the d18O values of the shells clearly showed life history that was consistent with the annual growth lines on the outside of the shell. Overall our isotopic data suggest that the carbonate shell is a good proxy for investigating the climate change and marine environments that the animal experienced (mainly from d18O), but the effects of ocean acidification along the Washington coast (mainly from d13C) are open to question