Clumped isotopic signatures in land-snail shells revisited: Possible palaeoenvironmental implications

It is crucial to understand the clumped isotope compositions (Delta(47)) of modern land-snail shells and their relationship with environmental parameters for palaeoenvironmental-studies. Previous studies have shown significant variations in relationships between snail-shell Delta(47) and ambient air temperature, and the reliability of shell Delta(47) in indicating air temperature remains uncertain. This study examined the shell Delta(47) from China with mean annual temperatures ranging from 5 to 23 degrees C and the snail body fluid delta O-18 estimated from shell delta O-18 and Delta(47)-derived temperatures. For all snails studied in this study, site-averaged Delta(47) values yield snail calcification temperatures ranging from 25 to 36 degrees C, which are higher-than-expected in either environmental temperatures or estimated snail activity temperatures. We suggest that snails up-regulate their body temperatures towards their preferred living conditions likely through behaviour or/and physiology adaptation, especially at low temperature environments, which is likely significant than observed previously. Delta(47) disequilibrium associated with CO2 degassing during snail calcification is potential but it could possibly be corrected by using an empirical calibration based on natural land-snails. Varying degrees of delta O-18 enrichment (> 8 parts per thousand) relative to rainwater are observed in snail body fluids, possibly due to variable evaporation during shell calcification. Coupled with model calculations, the relationship between snail body fluid delta O-18 and rainwater delta O-18 could be improved by using Delta(47)-based temperature and delta O-18 thermometry, if snails prefer to be active at similar to 90% relative humidity. This study highlights the importance of land-snail shell Delta(47) coupled with shell delta O-18 to indicate temperature and rainwater delta O-18 at micro-environments scales.