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

Land snails are widely distributed animals whose clumped isotope (Delta(47)) in shell carbonates can serve as a proxy for temperature in terrestrial environments. However, it is unclear whether the Delta(47) values of snail shells are affected by biological processes known as vital effects. Here, we report Delta(47) values of whole Achatina fulica snail shells cultured at different temperatures at different growth ages (samples collected monthly). In general, the mean Delta(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 Delta(47) temperatures (T-47) using the calibrations from Petersen et al. (2019), Bonifacie et al. (2017), and Kelson et al. (2017) are similar to 6 degrees C higher than the actual growth temperatures. Interestingly, this overestimation in T-47 disappears when applying Zhai et al.'s (2019) calibration for the Bradybaena snail. This calibration also yields good agreement between the T-47 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 Delta(47) with snail age and the correlations between Delta(47), delta O-18, and delta C-13 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.

Automated summary

The study found that the Delta(47) values of land snail shells decrease with higher cultivation temperature, indicating their potential use in reconstructing temperature changes. However, the reconstructed temperatures using different calibration methods may overestimate the actual temperatures. The vital effect, possibly explained by kinetic fractionation through CO2 degassing associated with dehydration/dehydroxylation during shell formation, is suggested as a factor influencing the Delta(47) values of snail shells.