Intra-shell stable isotopes in land snail as proxies of seasonal climate variability: Ontogenetic evidence from cultured and field specimens

• Intra-shell δ 18 O and δ 13 C were analyzed in lab-cultured and wild land snails. • The impact of ontogenetic growth could induce enrichment in intra-shell δ 18 O. • δ 13 C shell enrichment in cultured snails is linked to ontogenetic carbonate ingestion. • Wild δ 18 O shell profiles track seasonal precipitation with minimal physiological bias. Land snail shells preserve stable oxygen and carbon isotope compositions ( δ 18 O shell and δ 13 C shell ) that offer valuable seasonal to weather-scale records of terrestrial environmental changes. However, the extent to which ontogenetic processes influence these signals remains insufficiently understood. Here, we investigated intra-shell isotopic variations in giant African land snails from laboratory cultured Achatina fulica and field collected Lissachatina fulica from Panzhihua, China. Laboratory experiments show that adult snail exhibits a δ 18 O shell enrichment of up to 0.8‰, likely driven by internal physiological processes such as biomineralization and metabolism. In addition, δ 13 C shell show an enrichment of 1.3‰ in subadult and adult shells, potentially associate with increased carbonate ingestion. In natural settings, intra-shell δ 18 O shell variations primarily reflects seasonal fluctuation in precipitation δ 18 O, with physiological effects exerting only a minor influence. Although δ 13 C shell values in wild snails fall within the expected range of C 3 plant-based diets, the potential roles of carbonate ingestion and dietary selectivity should be considered when reconstructing vegetation isotope signatures. These findings establish land snail shells as robust proxies of sub-annual climate variability and offer a modern calibration framework to enhance the use of terrestrial biocarbonates in paleoclimate reconstructions, particularly across monsoonal and moisture-sensitive regions.