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