PALEOCLIMATE RECONSTRUCTION USING TROPICAL BIVALVES FOR A LUCAYAN ARCHEOLOGICAL SITE, SAN SALVADOR ISLAND, BAHAMAS

This research investigates the Holocene paleoclimate of the Bahamas Platform by comparing oxygen isotope records constructed from four modern and four archeological specimens of the bivalve, Codakia orbicularis, collected from Pigeon Creek lagoon and Pigeon Creek Archeological Site (AD 1450) on San Salvador Island.  In addition, sclerochronological analysis was performed to determine if light and dark growth bands observed in shell carbonate recorded seasonality comparable to the isotope records.

The stable isotope profiles for modern Codakia accurately recorded sea surface temperatures measured at Pigeon Creek lagoon.  The d¹⁸O values for the modern specimens ranged from –1.04 to +0.70‰ and averaged –0.22‰ while d¹⁸O values for the archeological specimens ranged from –1.18 to +1.31‰ and averaged +0.20‰.  The oxygen isotope profiles for the four modern specimens were similar, as were the profiles from the archeological specimens.  On the other hand, the two groups were isotopically distinct, suggesting that sea surface temperature or the d¹⁸O of surface waters differed between AD 1450 and today.  The archeological specimens of Codakia had significantly higher maximum d¹⁸O values per cycle; this could reflect a cooler and/or drier climate in the past.  On a yearly basis, the range of d¹⁸O values for the archeological samples was larger than the modern samples, suggesting that temperatures may have varied more widely throughout the year as well.

Growth increments in the shell, viewed as light and dark bands in reflected light, did not correlate with annual cycles of the oxygen isotope records in any predictable way as multiple dark bands were observed within most of the isotopic records.  This contrasts with previous studies that suggest dark bands represent annual winter growth checks and has implications for age determinations based on shell structure alone.