Environmental implication from stable carbon and oxygen isotope of live and archaeological shells and opercula of Turban snails from Hengchun Peninsula and Kenting site, Taiwan

[[abstract]] To examine when the ?18O values of Turban snail shells and opercula reach the isotopic equilibrium with ambient seawater and unravel the paleoenvironment of ~4,000 B.P. in southern Taiwan, this study analyzed the stable isotopic compositions of eight alive Turban snails (two Turbo setosus, five T. chrysostomus and a T. sparverius) collected from Hengchun Peninsula and five opercula of T. argyrostoma collected from Kenting site, Hengchun. The ?13C values of modern snail shells and opercula are between 0.38 and 2.10? (1.46±0.30?; 1σ; N=365) and 0.65 and 2.80? (1.76±0.44?; 1σ; N=482), respectirely. The ?18O values of modern snail shells and opercula are between -2.40 and -0.14? (-1.54±0.51?) and -2.40 and 0.25? (-1.40±0.53?), respectirely. ?13C values of seven modern opercula are significant different from those of complimentary shell. Based on the sea water temperature from O-luan-pi buoy and measured ?18O of seawater (?18O = 0? SMOW for summer and ?18O = 0.14? SMOW for winter), the ?18O values of aragonite precipitated in equrlibrium should be between -2.65? and 0.06?. Because most of the ?18O values of modern Turban snail shells and opercula are within this range, the ?18O values of modern Turban snail shells and opercula are in apparently isotopic equibrium with the seawater they lived in. The ?18O values of the five archaeological T. argyrostoma opercula are between -2.71 and 0.28? (-1.54±0.58?; 1σ; N=266). Assuming the ?18O values of seawater was simlar to that of present, the calculated oxygen isotope temperature is between 21.5℃ and 31.5℃ for ~4,000 B.P. and was roughly 2℃warmer than present. Based on the ?18O records, most of the archaeological snails were collected in winter and spring. ?13C 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.