Precipitation δ¹⁸O paced the seasonal δ¹⁸O variations of terrestrial snail body water and shells in the East Asian monsoon region

Terrestrial snails are sensitive to climate changes and their shell's oxygen isotope composition (δ¹⁸O_shell) is widely used in studies of paleoclimate reconstructions. However, the interpretation of δ¹⁸O_shell remains complex due to the combined effects from different factors such as precipitation δ¹⁸O (δ¹⁸O_p), relative humidity (RH), and temperature. Furthermore, no systematic studies have addressed the transformation of oxygen isotope signals from rainfall to the aragonite shell via snail body water. Here we present the results of Cathaica fasciola body water δ¹⁸O (δ¹⁸O_BW) and its content, which were sampled every two days throughout the growing season in 2021 in Xi'an. Meanwhile, the soil water δ¹⁸O (δ¹⁸O_SW), δ¹⁸O_p, rainfall amount, RH and temperature were also simultaneously monitored, and two high-resolution (at ∼0.3 mm interval) δ¹⁸O_shell series were obtained from two live snails collected in September and October 2021, respectively. These data reveal that the δ¹⁸O_BW mimic the variations of δ¹⁸O_p, and they are positively correlated (r² = 0.84) for precipitation events and the correlation coefficient only increases slightly (r² = 0.88) when RH is included in the multivariate analysis. During non-precipitation intervals, there is an obvious negative correlation between δ¹⁸O_BW and RH. Moreover, the variations of two δ¹⁸O_shell series are broadly consistent with the theoretically calculated δ¹⁸O_shell from δ¹⁸O_BW/δ¹⁸O_p at seasonal scale. Collectively, this study demonstrates that δ¹⁸O_p is the first-order control on the seasonal variations of δ¹⁸O_BW and δ¹⁸O_shell, while RH play its role during non-precipitation periods. Importantly, this study lays good foundation for reconstructing terrestrial seasonal distribution of precipitation and extreme rainfall events using fossil shells in the geological past.