SCHLEROCHRONOLOGY AND OXYGEN-18 ANALYSIS OF 18TH CENTURY CRASSOSTREA VIRGINICA SHELLS FROM THE CHESAPEAKE BAY: SIGNIFICANCE FOR ARCHAEOLOGY AND PALEOCLIMATE

Sea level rise represents a major threat to archaeological archives used in the reconstruction of pre-industrial climate. The eastern oyster, Crassostrea virginica, native to the Chesapeake Bay, is one such archive that records changes in water temperature and salinity in its carbonate shell. We analyzed four modern eastern oyster specimens from the present-day Chesapeake Bay and eight archaeological specimens from the infilled slave quarters at Stratford Hall, Virginia. The growth bands on the larger internal umbo of each oyster shell were photographed using a scanning electron microscope. Sampling for recovery of δ¹⁸O values was concordant with growth banding. Comparison of modern oyster δ¹⁸O_shell values with modern δ¹⁸O_water values reveals that the oysters precipitate their shell in isotopic equilibrium with the surrounding water. The archaeological oysters were stratigraphically labelled AA at the top layer to Y at the bottom layer during extraction and ¹⁴C dated to ~1756 CE for the bottommost shell and to ~1779 CE for the topmost shell. These ¹⁴C dates agree with archaeological documentation that dates the infill between the 1740s and the 1770s, just prior to the Stratford Hall Plantation’s economic decline. Pairing archaeological oyster δ¹⁸O values with SEM-based growth band measurements suggests a multidecadal change from a colder climate to a warmer climate with more seasonal variability from the mid to late 1700s during the Little Ice Age. This agrees with previous records from Chesapeake Bay sediment cores, suggesting that C. virginica is a promising archive capable of recording snapshots of high-resolution seasonal climate variability. Our work also demonstrates how seasonal variability may have influenced the working operations at Stratford Hall. More so, we highlight the importance of preserving the natural archives at archaeological sites, as historical C. virginica shells may be the next lost paleoclimate archive because of climate change and rising sea levels.