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 theprehistoric temperature and salinity of the waters in which they grew.While the use of carbonatepaleoclimate archives to determine past climate conditions is a well-established practice, thevast majority of these studies arebiased towards corals, leaving large parts of the mid-to-upperlatitudes bereft of records. The need for information on past climate conditions grows everpressing as our current climate undergoes rapid change, so areas such as the North Carolinacoast need further documentation. Archeological Mercenaria mercenaria shells were excavatedfrom 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 highresolution oxygen and carbon isotope values (d18O and d13C), and thenwere compared todata of modern shells of the same species collected within the same area on the NorthCarolina coast. Thed18O andd13C values obtained from the midden shells indicate similar wintertemperatures and salinity for both modern and prehistoric climates, but a colder and/or drierprehistoric summer. The Roman Warm Period is reported to have variable climate in differentregions of the world (warm/cold, dry/wet), but drier conditions are reported in Florida. The higherd18O and d13C values seen in the Roman Warm Period summers could be an indicator of lesssummer precipitation leading to higher salinity. This suggests that similar to Florida, the RomanWarm Period also had less summer precipitation in coastal North Carolina.