Ocean acidification indications from stable isotope analyses in carbonate shells and otoliths

The carbonate chemistry of the world’s oceans has been changing due to the anthropogenic CO2 sinking into ocean and caused seawater pH to decrease and seawater temperature to increase. Ocean acidification will lead to a... [ view full abstract ]

The carbonate chemistry of the world’s oceans has been changing due to the anthropogenic CO₂ sinking into ocean and caused seawater pH to decrease and seawater temperature to increase. Ocean acidification will lead to a shift in DIC (dissolved inorganic carbon) equilibria and result in higher CO₂ and lower carbonate ion (CO₃^2-) concentrations. This will affect the carbonate saturation state (Ω). The impacts of climate change thus can be revealed from stable carbon and oxygen isotope ratios (¹³C/¹²C or d¹³C, and ¹⁸O/¹⁶O or d¹⁸O) and the isotopic fractionation between blood DIC and the carbonate proxies of shells and otoliths. In this study, we report the results of using d¹³C values in detection of ocean acidification from shells of Pacific razor clam (Siliqua patula), Pacific geoduck (Panopea abrupta), and Pacific sea scallop (Patinopectin caurinus) along the Washington west coast; and using the d¹⁸O variations in study of climate driven regime shifts for Atlantic cod (Gadus morhua) and Pacific halibut (Hippoglossus stenolepis) populations. Among the carbonate powder samples analyzed the d¹³C values of the clam shells ranged from -2.88‰ to -0.30‰, whereas d¹⁸O values of the same samples ranged from -2.16‰ to +1.39‰. Overall our research suggests that the shell carbonate is a good proxy for reconstructing the life history of the clam and detecting the effects of ocean acidification by d¹³C signatures. The d¹⁸O records of otoliths, in contrast, are useful techniques in examining the decadal-scale (e.g., the last 20-30 yrs) regime shifts that an individual fish encountered.