Annual cycle of ¹⁸O/¹⁶O and ¹³C/¹²C isotope ratios in landsnail shells

Monthly data on the isotopic composition of carbon and oxygen in shells of the land snail, Theba pisana, were collected from two localities near Ashqelon, Israel. Seasonal trends in the isotopic data from the two areas were similar. However, significant month-to-month and locality-to-locality differences in the δ¹³C- and δ¹⁸O-values of the snail shell carbonate indicate that microenvironmental diversity did indeed exist. We suggest that the factors responsible for the microclimatological diversity, such as plant coverage and primary productivity, control the degree of evaporation of “interface water” at the soil—air boundary. We used the oxygen isotopic composition of snail shell carbonate to calculate the isotopic composition of this “interface water”, and the δ¹³C-values of snail shell carbonate to monitor the amount of heterotrophic CO₂ production in the soil.