Comparison of modern and Roman Warm Period seasonal climate in coastal North Carolina using isotope sclerochronology of archaeological shells.

Bivalve shells collected from archeological dig sites contain geochemical records of the prehistoric temperature and salinity of the waters in which they grew. While the use of carbonate paleoclimate archives to determine past climate conditions is a well-established practice, the vast majority of these studies are biased towards corals, leaving large parts of the mid-to-upper latitudes bereft of records. The need for information on past climate conditions grows ever pressing as our current climate undergoes rapid change, so areas such as the North Carolina coast need further documentation. Archeological Mercenaria mercenaria shells were excavated from a midden on Davis Island, NC dating to the Roman Warm Period (ca. 800 BC - AD 500, based on pottery). Carbonate samples drilled from the shells were processed to obtain high resolution oxygen and carbon isotope values (d¹⁸O and d¹³C), and then were compared to data of modern shells of the same species collected within the same area on the North Carolina coast. The d¹⁸O and d¹³C values obtained from the midden shells indicate similar winter temperatures and salinity for both modern and prehistoric climates, but a colder and/or drier prehistoric summer. The Roman Warm Period is reported to have variable climate in different regions of the world (warm/cold, dry/wet), but drier conditions are reported in Florida. The higher d¹⁸O and d¹³C values seen in the Roman Warm Period summers could be an indicator of less summer precipitation leading to higher salinity. This suggests that similar to Florida, the Roman Warm Period also had less summer precipitation in coastal North Carolina.