EFFECT OF pH ON MOLLUSK SHELL CARBON AND OXYGEN ISOTOPES

Oxygen and carbon isotopes in biogenic carbonates are a powerful tool for reconstructing past environmental and climatic change. It is known that pH can affect isotope ratios in foraminifera, but little is known about such effect on other biogenic carbonates in different taxa. Increasing CO₂ in the earth’s atmosphere has a direct influence on the carbonate chemistry of oceans; as atmospheric CO₂ is absorbed by surface ocean waters, these waters experience a significant reduction in pH and altered carbonate chemistry. We raised larvae of the eastern oyster, Crassostrea virginica, at pre-industrial (280 ppm) and elevated levels (800 ppm) of atmospheric CO₂, to mimic future and past pH/carbonate chemistry conditions in order to investigate the potential impacts on stable isotope fractionation in larval shells. Prior to metamorphosing, the larval shells were removed from experimental cultures and prepared for δ ¹³C and δ ¹⁸O analysis. Additionally, water samples and algae samples were taken to determine total alkalinity, δ ¹³C-DIC, and δ ¹⁸O_water, along with organic measurements for the algae food source. Using data from all potential carbon sources enabled us to investigate whether pH also controls the amount of metabolic carbon incorporated in the larval shell. This is the first study to investigate the impact of pH on mollusk shell isotopes.