Clumped Isotope Data from Gar Scale Bioapatite Samples and Lab Standards

We measured the clumped isotope, Δ47, composition of the carbonate in the bioapatite of modern gar scales from 19 specimens collected from eight locations in North America, with mean water temperatures ranging from 11.3 to 27.0 °C. Samples were reacted at 90 °C and standards were reacted at both 25 °C and 90 °C. Samples and standards were run on a MAT 253 dual-inlet gas-source isotope ratio mass spectrometer (Thermo Scientific, USA) housed at the Yale University Analytical and Stable Isotope Center. Raw data was processed using the most up-to-date methods (Petersen et al., 2019). Our sample reproducibility was 0.021‰ (1 SD). Our standards included cylinder CO2 (Airgas, USA), CO2 equilibrated with water at 25 °C and 50 °C, Carrara marble, and the ETH carbonate anchors. Δ47 data is presented as ‰, InterCarb-Carbon Dioxide Equilibrium Scale (I-CDES) 90 °C for samples and standards reacted at 90 °C and I-CDES 25 °C for standards reacted at 25 °C.

We use modern climate data from Daymet V4 (Thornton et al., 2022). We convert variable water temperatures into an effective temperature Te, which accounts for the influence of temperature on growth rate. Te for our gar samples ranges from 13.8 to 27.1 °C. We used this dataset to create a new calibration relating temperature to the Δ47 in gar scale bioapatite. The resulting calibration curve is: Δ47 = (0.1206 ± 0.0171) x 106/Te2 – (0.7429 ± 0.0587) (1 SE), with R2 = 0.75.