Environmental Information Inferred from the Stable Carbon and Oxygen Isotopes of Live and Archaeological Turban Snails from Hengchun Peninsula, Southern Taiwan

To examine whether the δ¹⁸O values of Turban snail shells and opercula reach the isotopic equilibrium with ambient seawater and to unravel the paleoenvironment of southern Taiwan in ~4,000 B.P., this study analyzed the isotopic compositions of eight live Turban snails (two Turbo setosus, five T. chrysostomus and one T. sparverius) collected from Hengchun Peninsula and five opercula of T. argyrostoma collected from Kenting site, Hengchun, southern Taiwan.

Mean δ¹³C values of modern snail shells and opercula are 1.46 ± 0.30‰; (1σ; N = 365) and 1.76 ± 0.44‰ (N = 481), respectively. Average δ¹⁸O values of modern snail shells and opercula are respectively -1.55 ± 0.51‰ and -1.40 ± 0.53‰. δ¹³C values of six modern opercula are 0.2 to 0.6‰ greater than those of associated shells. There is no significant difference in most of the δ¹⁸O values between opercula and associated shells except that the δ¹⁸O values of T. setosus opercula are 0.3‰ greater than those of associated shells. Based on the sea water temperature records (2003-2006; Central Weather Bureau, Taiwan) and the available δ¹⁸O of seawater records (1992-1995; 0.02‰ for summer and 0.37‰ SMOW for winter; Shen et al., 2007:EPSL, v. 237, p. 370), almost all of the δ¹⁸O values of modern Turban snail shells and opercula reach the apparently isotopic equilibrium with the seawater they lived in.

Mean δ¹⁸O value of the five archaeological T. argyrostoma opercula is -1.53 ± 0.58‰ (N = 266). Assuming the δ¹⁸O values of seawater of ~4,000 B.P. were similar to those of present, the calculated mean oxygen isotope temperature of ~4,000 B.P. was roughly 0.7 °C warmer than that of present. Mean δ¹³C values of the archaeological opercula (3.33 ± 0.49‰) are 1.57‰ greater than those of modern opercula suggesting that the hydrological condition was different from present.