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

摘要

Stable isotopes of land snail fossil shell carbonates (δ~(13)C_(shell) and δ~(18)O_(shell)) provide the opportunity to decipher paleodietary and paleoenvironmental changes. However, the environmental meanings of δ~(13)C_(shell) and δ~(18)O_(shell) remain elusive especially in the monsoonal climate region. To elucidate this, δ~(13)C_(shell) and δ~(18)O_(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, δ~(13)C_(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 δ~(13)C_(shell) documents a C_3/C_4 mixing signal and exhibits only a strong altitude effect. δ~(18)O_(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 δ~(18)O_(shell) than Bradybaena, which suggests that the two land snails have different ecophysiological traits, and the δ~(18)O_(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.