Oxygen isotope variability in Crassostrea Virginica shell from the Chesapeake Bay: applications to regional paleoclimate

by Cheyenne Palmo

Faculty mentor: Dr. Pamel Grothe

Future climate predictions in the Chesapeake Bay region suggest unprecedented warming (Cronin et al., 2003) and more intense periods of rainfall (Najjar et al., 2010). In order to quantify present and future changes in climate variability, we need a long baseline of natural climate variability that extends far beyond the instrumental record. Paleoclimate records can be used to help quantify anthropogenic climate change from natural climate variability. However, reconstructing regional climate in an estuary system is challenging, resulting in a lack of pre-instrumental era climate records for the Chesapeake Bay. The Common Eastern Oyster, Crassostrea Virginica, is a promising natural archive to reconstruct natural, or pre-industrial, climate in the Chesapeake Bay region. Stable oxygen isotopes (δ18Oshell) recorded in their calcium carbonate shell are indicators of both changes in temperature and the δ18O of the water (δ18Osw), which is typically a function of salinity. In this study, the δ18Osw and δ18Oshell values were analyzed to understand how the variability in the δ18O of Crassostrea Virginica calcium carbonate shell reflects changes in sea surface temperature and salinity in the Chesapeake Bay in order to validate it as a paleoclimate archive. The oysters were sampled along their banded growth structure, providing yearly resolution for isotopic analysis. We predict that the δ18O of the oyster shell will reflect the same δ18O trends as the water, meaning the shells will precipitate at isotopic equilibrium. Additionally, we predict that salinity, dependent on temperature and precipitation, is the primary driver for changes in δ18O of the shell, whereas increased δ18Oshell values reflect higher salinity values. This work will provide the foundation for understanding the controls between estuarine water and shell geochemistry, with the potential to apply this relationship to regional paleohydrology and paleoclimate reconstruction using fossil Crassostrea Virginica shells.