THE BIVALVE GLYCYMERIS AMERICANA AS A RECORD OF SCLEROCHRONOLOGICAL AND ISOTOPIC TEMPERATURE DATA FROM THE CHARLESTON SEA (LATE PLIOCENE TO RECENT)

The early Pliocene to the late Quaternary represents a climate transition from significantly higher than present global mean surface temperature to maximum glaciations. Boundary conditions for climate model reconstructions for the Early to Middle Pliocene (Williams et al., 2009) and Last Glacial Maximum (Otto-Bliesner et al., 2007) are primarily based on multiple proxies from the Albemarle and Okeechobean Sea basins of Middle Atlantic Coastal Plain, USA. High-resolution sclerochronological data from the Charleston Sea, the region between the Albemarle and Okeechobean basins, is significantly under sampled. The purpose of the study is to help fill in a data gap along the western North Atlantic.

We evaluated the potential of Glycymeris americana as an environmental indicator for the Charleston Sea by applying sclerochronological techniques on sample sets of the cockles collected from Duplin Formation (2.8-2.3 Ma), Waccamaw Formation (1.8-1.5 Ma) and recent (1970s) shelf deposits. Growth increments in acetate peels of the hinge and valve regions indicate a maximum longevity of the analyzed shells of 76 years. Seafloor temperatures calculated from shell carbonate stable oxygen isotope ratios (δ¹⁸O) give minimum and maximum values of 9.63 ± 1.2 ⁰C and 23.77 ± 0.4 ⁰C in the Duplin Fm., 10.12 ± 0.6 ⁰C and 21.79 ± 0.4 ⁰C in the Waccamaw Fm, and 17.96 ± 1.2 ⁰C and 25.97 ± 0.4 ⁰C on the recent shelf. Mean annual temperature ranges from fossil and sub-fossil G. americana exhibit similar temperature ranges to the instrumentation south of Cape Hatteras, within the recent Charleston Sea region.