OXYGEN ISOTOPE VALUES OF CRASSOSTREA VIRGINICA SHELL FROM CHESAPEAKE BAY: APPLICATIONS TO REGIONAL PALEOCLIMATE

Future climate predictions in the Chesapeake Bay region suggest unprecedented warming with more increasing rainfall. In order to quantify contemporary and future changes in climate variability, requires development of proxy records of variability that extend back in time beyond the instrumental record. Paleoclimate records can be used to help differentiate anthropogenic climate forcing from natural climate variability. However, reconstruction of regional climate in an estuarine systems is challenging, resulting in minimal pre-instrumental era climate records for the Chesapeake Bay. The Common Eastern Oyster, Crassostrea virginica, is a promising natural archive for reconstruction of natural, pre-industrial, environmental conditions in the Chesapeake Bay region. Stable oxygen isotope values (δ¹⁸O_shell) archived in their calcium carbonate shell conflate changes in temperature and the δ¹⁸O of the water (δ¹⁸O_sw). δ¹⁸O_swvalues are in turn forced by meteoric precipitation and salinity. In this study, δ¹⁸O_swand δ¹⁸O_shellvalues are utilized to better understand variability in sea surface temperature and salinity in the Chesapeake Bay in order to establish a new paleoclimate archive. Surface and deep (deep usually implies >100m, or sometimes >5,400m depth) water samples were collected at established oyster reefs in the Rappahannock River, Virginia. In collaboration with the Virginia Institute of Marine Science, oysters were collected at four established reefs in the Rappahannock River. The oysters were sampled along their banded growth structure, providing yearly resolution for isotopic analysis. We anticipate that the δ¹⁸O values of the shells will precipitate at isotopic equilibrium, thereby providing a longer-term record of variability in temperature and salinity than that currently available. Because salinity, temperature, and meteoric precipitation, are the primary drivers of δ¹⁸O_shell, we expect that higher δ¹⁸O_shell values should reflect periods of higher salinity. This work will provide the foundation for a better understanding of the relationship between estuarine water and shell geochemistry in Chesapeake Bay, using this relationship to develop regional paleohydrology and paleoclimate reconstructions using sub-fossil Crassostrea virginica shells.