Diet control on carbon isotopic composition of land snail shell carbonate

Carbon isotope compositions for both the carbonate shells and soft bodies (organic tissue) of living land snails collected mostly from the Loess Plateau, China have been measured. The result shows that delta C-13 values range from -13.1 parts per thousand to -4.3 parts per thousand for the aragonite shell samples and from -26.8 parts per thousand to -18.0 parts per thousand for the soft body samples. Although the shells are enriched in (13) C relative to the bodies averagely by 14.2(+/- 0.8)parts per thousand, the shell delta C-13(a), values are closely correlated to the body delta C-13(org) values, expressed as delta C-13(a) = 1.021 delta C-13(org) + 14.38 (R = 0.965; N = 31). This relationship indicates that 813 Ca is primarily a function of the isotopic composition of the snail diets since previous studies have proved that the snail body is the same as their food in carbon isotope composition. In other words, carbon isotope composition of the carbonate shell can be used as a proxy to estimate the dietary C-13 abundance of the land snails. The data also support that the C-13 enrichment of the carbonate shells results mainly from the equilibrium fractionations between the metabolic CO2, HCO3- in the hemolymph and shell aragonite, and partially from kinetic fractionations when snail shells form during their activity.