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[MIS18-P21] Estimation of kinetic biases in dual clumped isotopes (Δ47 and Δ48) of various types of carbonates
Keywords:Carbonate clumped isotopes, Δ47, Δ48, Disequilibrium effect, Temperature reconstruction
Carbonate clumped isotope thermometry is a promising approach to reconstruct temperature which does not require knowledge of water δ18O. The principle of the method is based on the temperature dependency of abundance anomaly of 13C-18O bond (Δ47) relative to the stochastic abundance. It is however problematic to estimate temperatures from Δ47values of carbonates that were induced by CO2 degassing and absorption. CO2 degassing (e.g., in cases of speleothem and tufa) or absorption (e.g., in cases of coral and molluscan skeletons) can lead to isotopic disequilibrium in dissolved inorganic carbon pool and result in smaller or larger Δ47 values respectively. These kinetic biases lead to over- or under- estimations of deposition temperatures.
Recently, theoretical studies suggested that dual clumped isotopes (Δ47 and Δ48) analyses can identify such kinetic biases (Guo and Zhou, 2019; Guo, 2020). In early stage of CO2 degassing (absorption), Δ47 of carbonate shows negative (positive) departure from the expected equilibrium value, whereas Δ48 shows positive (negative) departure. The kinetic slopes of their relations can be theoretically predicted.
To date, we have measured Δ48 values of various types of carbonates, together with Δ47 values. For example, we found that Δ47 values of Japanese natural tufa show negative departure (0.011–0.012‰) from the equilibrium value (Kato et al., 2019) and similar Δ47 departure was also found in a Japanese stalagmite (Kato et al., 2021). On the other hand, Δ48 values of the tufa samples show positive departure (around 0.03–0.05‰).
In this study, we show the results of dual clumped isotopes analyses for various types of carbonates such as synthetic calcite, tufa, stalagmite, fish otolith, and coral skeleton to estimate the kinetic biases in their Δ47 and Δ48 values.
Reference
Guo, W. & Zhou, C. 2019, GCA 267, 196–226.
Guo, W. 2020. GCA 268, 230–257.
Kato et al. 2019. GCA 244, 548–564.
Kato et al. 2021. QSR 253, 106746.
Recently, theoretical studies suggested that dual clumped isotopes (Δ47 and Δ48) analyses can identify such kinetic biases (Guo and Zhou, 2019; Guo, 2020). In early stage of CO2 degassing (absorption), Δ47 of carbonate shows negative (positive) departure from the expected equilibrium value, whereas Δ48 shows positive (negative) departure. The kinetic slopes of their relations can be theoretically predicted.
To date, we have measured Δ48 values of various types of carbonates, together with Δ47 values. For example, we found that Δ47 values of Japanese natural tufa show negative departure (0.011–0.012‰) from the equilibrium value (Kato et al., 2019) and similar Δ47 departure was also found in a Japanese stalagmite (Kato et al., 2021). On the other hand, Δ48 values of the tufa samples show positive departure (around 0.03–0.05‰).
In this study, we show the results of dual clumped isotopes analyses for various types of carbonates such as synthetic calcite, tufa, stalagmite, fish otolith, and coral skeleton to estimate the kinetic biases in their Δ47 and Δ48 values.
Reference
Guo, W. & Zhou, C. 2019, GCA 267, 196–226.
Guo, W. 2020. GCA 268, 230–257.
Kato et al. 2019. GCA 244, 548–564.
Kato et al. 2021. QSR 253, 106746.