Terrestrial gastropods are used to understand paleoclimate and paleoecosystems because they have long lasting shells and small individual geographic ranges. In this study, we use the climatic variation of the LA Basin to investigate environmental and biological controls on the carbonate clumped isotopic signatures and traditional oxygen (O) stable isotope signatures of modern terrestrial gastropod shells. Previous work on gastropod shells over the last several decades have focused on 18O/16O, yet several factors affect gastropod O isotope budgets (e.g. temperature and body water 18O/16O ratios) making it difficult to interpret. Work over the past decade has shown carbonate clumped isotope methods (based on 13C-18O abundance) may more accurately constrain gastropod shell growth temperature and thus be used in concert with shell 18O/16O to reconstruct body water 18O/16O values. However, the systematics of clumped isotope signatures in biologically derived carbonates are still poorly understood.
We collected individuals of the introduced species Cornu aspersum from around the LA basin. During collection, we euthanized and stabilized individuals in ethanol prior to cleaning and analysis. We then analyzed the shells for O and carbonate clumped isotopes at the UCLA Clumped Isotope and Stable Isotope Facility. Lastly, we compared clumped isotope-derived temperature and water 18O/16O estimates to local weather station data and regional precipitation O isotope data to test the accuracy of the method.
Results/Conclusions
Preliminary results indicate that across all sites clumped isotope derived temperatures (16.9 °C) accurately capture the mean wet season (December through February) temperatures (~16 °C). We measured no significant inter-site differences in temperature, likely due to intra-site variability and the homogeneity of wet season temperatures at the different sites. If these results hold, they indicate that clumped isotope signatures of gastropod shells can be used to understand environmental temperature trends at landscape scales but are too variable for use in localized site by site comparisons spanning a range of conditions similar to what we have sampled.
The calculated 18O/16OVSMOW of formation fluid for the snail shells that we measured ranges between -5.6‰ and -1.3‰. Unlike the temperature estimates, there are significant differences between sites that indicate snail shells may be applied to sub-landscape scale analyses.