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 δ¹³C values range from −13.1‰ to −4.3‰ for the aragonite shell samples and from −26.8‰ to −18.0‰ for the soft body samples. Although the shells are enriched in ¹³C relative to the bodies averagely by 14.2(±0.8)‰, the shell δ ¹³C_a values are closely correlated to the body δ ¹³C_org values, expressed as δ ¹³C_a = 1.021 δ ¹³C_org + 14.38 (R = 0.965; N = 31). This relationship indicates that δ ¹³C_a 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 ¹³C abundance of the land snails. The data also support that the ¹³C enrichment of the carbonate shells results mainly from the equilibrium fractionations between the metabolic CO₂, HCO ₃ ⁻ in the hemolymph and shell aragonite, and partially from kinetic fractionations when snail shells form during their activity. Supported by the Chinese Academy of Sciences (Grant No. KZCX2-SW-133) and the National Natural Science Foundation of China (Grant Nos. 40021202 and 40373046)