Evaluation of Land Snails for Clumped Isotope Paleothermometry: A Case Study of the Pleistocene of Bermuda

Abstract

With the advent of clumped isotope analyses, sources of data that were previously not of use in determining paleoenvironment may become valuable proxies for the reconstruction of past Earth surface temperatures. Land snails, for example, may prove to be useful paleothermometers. It was found that clumped isotope analyses of land snails of the genus Poecilozonites in Bermuda do yield reasonable paleoclimate estimates for that region at the time of shell formation during interglacial stage 5e (~125 kyrs). One factor that must be further investigated, however, is the degree to which the ecology of the snails may bias temperature estimates because of differences between ambient conditions and the internal body temperature and water composition of the land snails. An independent estimate of paleotemperature, consisting of clumped and standard δ18O analyses, were completed on a coeval marine snail, Cittarium pica, collected from Stage 5e coastal carbonates. This individual snail provides an excellent record of annual seasonality. Moreover, based on combined δ18O and clumped isotope analyses, this specimen suggests considerably lower Stage 5e surface temperatures (~ 8°C cooler) than recorded today. While temperature estimates based on land snail carbonates are in close agreement with prior reconstructions, their reliability in recording ambient temperature remains unproven.