Stable Carbon and Oxygen Isotopes in Shell Carbonates of modern Land Snails in China and Their Relation to Environment Variables

Stable isotopes of land snail fossil shell carbonates (delta C-13(shell) and delta O-18(shell)) provide the opportunity to decipher paleodietary and paleoenvironmental changes. However, the environmental meanings of delta(13)Cshell and delta O-18(shell) remain elusive especially in the monsoonal climate region. To elucidate this, delta(13)Cshell and delta O-18(shell) of the two most common land snails in China, Cathaica and Bradybaena, were analyzed in this study. Results show that Bradybaena has a wider distribution than Cathaica and provides considerable potential for use in paleoenvironmental reconstruction. In addition, delta C-13(shell) of Bradybaena increases with altitude and temperature, decreases with mean annual precipitation, and reflects the isotopic signal of C-3 plants. In contrast, Cathaica delta C-13(shell) documents a C-3/C-4 mixing signal and exhibits only a strong altitude effect. delta O-18(shell) of Bradybaena decreases with mean annual precipitation in the Indian monsoon and westerlies regions but increases with mean annual temperature in the East Asian monsoon region; as a strong correlation exists between the two variables, they could thus potentially be used to reconstruct paleotemperatures. However, uncertainties should be recognized due to the complexity of the land-snails' ecophysiological responses to environmental changes. Cathaica has slightly lower delta O-18(shell) than Bradybaena, which suggests that the two land snails have different ecophysiological traits, and the delta O-18(shell) of Cathaica follows mean annual temperature in northeast China. This study lays a ground for explaining land snail stable isotopes in paleorecord in China and reasserts the importance of different ecophysiological traits of land snails in paleoclimatic research.