Clumped isotopic compositions of cultured and natural land-snail shells and their implications

Abstract Land snails are widely distributed animals whose clumped isotope (∆47) in shell carbonates can serve as a proxy for temperature in terrestrial environments. However, it is unclear whether the ∆47 values of snail shells are affected by biological processes known as “vital effects.” Here, we report ∆47 values of whole Achatina fulica snail shells cultured at different temperatures at different growth ages (samples collected monthly). In general, the mean ∆47 values of the snail shells decrease with higher cultivation temperature, which indicates they have potential use in reconstructing temperature changes. However, the mean reconstructed ∆47 temperatures (T47) using the calibrations from Petersen et al. (2019), Bonifacie et al. (2017), and Kelson et al. (2017) are ~6 °C higher than the actual growth temperatures. Interestingly, this overestimation in T47 disappears when applying Zhai et al.'s (2019) calibration for the Bradybaena snail. This calibration also yields good agreement between the T47 data of all field-collected snails and their growing season temperatures. The above-mentioned phenomenon indicates the existence of the vital effect in land-snail shells. The variations in ∆47 with snail age and the correlations between ∆47, δ18O, and δ13C values also indicate the potential influence of vital effects. Finally, we suggest that the vital effect may be explained by kinetic fractionation through CO2 degassing associated with dehydration/dehydroxylation during the formation of snail shells.