Clumped isotope thermometry (Δ₄₇) measurements in marine gastropods suggest equilibrium precipitation

The clumped isotope paleothermometer (Δ₄₇) has been used to reconstruct temperatures from various biogenic carbonate archives. Calibration studies demonstrate that some biogenic carbonates precipitate in Δ₄₇ equilibrium and record growth temperatures accurately (e.g., many bivalve mollusks), while others appear to exhibit disequilibrium, or ‘vital’, effects and yield isotopically reconstructed temperatures that are biased (e.g., shallow-water corals). These studies have largely excluded marine gastropods, so it is not known whether they tend to precipitate their shells in or out of isotopic equilibrium. In this study, we present seasonal-scale δ¹⁸O and seasonally targeted Δ₄₇ and Δ₄₈ measurements from modern marine gastropods representing 8 genera and 10 species, reconstructing apparent growth temperatures and screening for equilibrium precipitation. We find that most marine gastropods appear to precipitate in Δ₄₇ and Δ₄₈ equilibrium and faithfully record environmental temperatures, making them suitable for Δ₄₇-paleothermometry. A few gastropods (Caviturritella/Turritella sp., Campanile symbolicum, Megastraea undosa) appear to precipitate out of Δ₄₇ equilibrium, though these disequilibrium signatures may partially be explained by differences between actual growth temperatures and instrumental calibration temperatures (Caviturritella/Turritella sp., M. undosa) or differences between inner and outer layer precipitation (C. symbolicum). We present new Δ₄₇-temperature data for 2 Middle Eocene Campanile giganteum fossils collected from the Paris Basin and discuss how to interpret the results in the context of our modern samples. Finally, in conducting this calibration we demonstrate paired Δ₄₇/Δ₄₈ as an effective tool to screen for disequilibrium precipitation in marine gastropods.