LB 32-272 - Exploring phylogenetic patterns in mollusk shell geochemistry

Carbonate clumped isotope thermometry is a geochemical method to calculate the temperature of mineral formation from the excess of heavy bonds (13C - 18O) compared to a stochastic distribution. In the case of organisms that secrete calcium carbonate shells (CaCO3), we can use clumped isotopes to derive the temperature at which biomineralization occurred and ultimately as a proxy for the temperature of past environments. Applications of this geothermometer have been instrumental in elucidating environmental conditions from such proxies as corals, coccolithophores, foraminifera, and mollusks over the geologic record. Consequently, carbonate clumped isotope thermometry has the potential to be a powerful tool in paleoecology and paleoclimatology research.However, an outstanding question for the application of carbonate clumped isotopes in temperature reconstructions is whether the isotopic composition of a biominerals reflects its environment. Organisms of different species/genuses use various biomineralization strategies that can lead to varying degrees of disequilibrium with the environment. Recently, researchers have found phylogenetic signals in the elemental geochemistry of carbonate biominerals. This finding led to the exploration of how biocalcification mechanisms respond to changes in seawater carbonate chemistry. Based on these findings, we hypothesize that clumped isotope signatures of carbonate shells in the phylum Mollusca can be explained partly by phylogenetic relatedness. Carbonate clumped isotopes are reported as the value Δ47, in per mille (‰). Δ47 values are then used to calculate temperature (oC) using a community-vetted calibration equation. Here, we use the calibration line of Anderson et al., 2021, which is sensitive to low temperature reconstructions. Specimens were collected as deceased individuals, then drilled at the aperture for fine powder. Three aliquots of 0.5 ± 0.02 mg were analyzed on a Nu Perspective IRMS instrument.Preliminary Δ47 data from the Santa Monica Heal the Bay Aquarium samples: Kelletia kelletii (0.666 ‰), Norisia norrisii (0.610 ‰), and Tegula funebralis (0.652 ‰). These values correspond to temperatures of 3.2 oC, 19.7 oC, and 7.1 oC, respectively, compared to the aquarium water temperature of 15.5 ±1 °C. Two of the species (N. norrisii and T. funebralis) come from the Tegulidae family, indicating that there is greater variability within taxonomic family than compared to an outgroup. While preliminary, these results do not indicate a phylogenetic signal in the clumped isotope signatures of the gastropod species.