Sea level rise and a Florida mortuary pond: how oysters (crassostrea virginica) reveal past climate change at the Manasota key offshore archaeologyical site

Abstract

The Manasota Key Offshore archaeological site (Florida, USA) is a mortuary pond dated to 7214 ± 30 cal BP and consisting of modified wooden stakes and human burials preserved in peat. At the time, this freshwater pond was located inland of the coast and used as a place of interment by Florida’s indigenous population. Over the intervening years, sea levels altered the landscape and affected the mortuary pond, which is now in an offshore context. Archaeological excavations revealed oysters (Crassostrea virginica) attached to human skeletal and cultural material— a direct line of evidence of past sea level rise. Morphometric analysis, sclerochronology, radiocarbon dating, and stable isotope analysis of eight oysters demonstrated there were two distinct environments at the time of oyster growth, each representing separate time periods and water parameters. The earlier oyster group indicated fresher water parameters, and the later hinted at hypersaline conditions. Oysters expired at ages between one and three, suggesting delicate human skeletal material was exposed to the water column for equally as long and yet remained preserved. This is the first time oysters attached to Archaic period skeletal material were used to draw wider conclusions about past marine transgression and environmental change.