Technical Note: Developments and Applications in Triple Oxygen Isotope Analysis of Carbonates

Abstract

Triple oxygen isotope systematics has evolved as a powerful tool in understanding various earth system processes. It has proven reliable in assessing paleoenvironmental conditions from natural archives (e.g., waters, ice cores, biota, sediments, etc.) owing to recent advances in high-precision mass spectrometric analysis. Toward the standardization of triple oxygen isotope analyses in carbonates, we describe a procedure of high-precision Δ′17O analysis of carbonates by a two-step protocol: acid digestion of carbonates to evolve CO2 followed by the catalytic CO2–O2 exchange method. The Δ′17O values of a suite of carbonate reference materials and several carbonates of different origins have been determined with good precision (∼0.007‰). The accuracy of sample Δ′17O values is dependent on the accuracy of Δ′17O composition of the reference CO2 used in determining the effective fractionation (θs) in the experimental setup. The obtained Δ′17O values (λ = 0.528, versus VSMOW) for NBS18-CO2 (−0.119‰) and NBS19-CO2 (−0.169‰) show a difference of 0.050‰, similar to that obtained elsewhere via complete fluorination. The analyzed carbonates mostly conform to equilibrium mass-dependent fractionation laws, but we encountered a suite of samples from cold seeps, caves, and metasomatic environments that have Δ′17O values indicative of disequilibrium fractionation. We show that a combination of clumped isotope composition (Δ47) that provides estimates of formation temperature and triple oxygen isotope ratios in carbonates can help in reconstructing past environments, where paired carbonate data (δ13C−δ18O−Δ47–Δ′17O) and parent water data (δ17O−δ18O−Δ′17O) are particularly useful.

Reconstructing Past Elevations From Triple Oxygen Isotopes of Lacustrine Chert: Application to the Eocene Nevadaplano, Elko Basin, Nevada, United States

“…In this study we presented the first lacustrine chert triple oxygen isotope dataset from a Cenozoic basin in western North America and used this data, in conjunction with carbonate clumped isotope measurements to derive an elevation estimate for the eastern Eocene Nevadaplano. Future measurements on carbonates (e.g., Passey et al, 2014;Bergel et al, 2020;Fosu et al, 2020;Voarintsoa et al, 2020;Wostbrock et al, 2020) from the Elko Basin, specifically on the Elko Formation, would benefit from paired measurement of the carbonates from the Eocene to Miocene strata for both triple oxygen isotopes and carbonate clumped isotopes, allowing for issues for formation temperature associated with chert formation to be overcome. Nevertheless, state-of-the-art data sets presented here indicate that:…”

Temperature dependence of isotopic fractionation in the CO2‐O2 isotope exchange reaction

“…These observations are a consequence of a singular behavior of θ close to the crossover, a well described anomaly in isotope equilibria 32,71–75 . Nevertheless, the experimentally determined θ values may not represent the CO 2 ‐O 2 equilibrium exchange due to the possible thermal diffusion effect (see above) and other heterogenous process involving adsorption, desorption, and mixing 12,19,28,29 . As a result, the experimentally determined θ values are steady‐state values.…”

Temperature Estimates of Lower Miocene (Burdigalian) Coastal Water of Southern India Using a Revised Otolith “Clumped” Isotope Paleothermometer

“…Such an assumption has the potential to yield small inaccuracies in Δ 47 reconstructed values, depending on the composition of the mass spectrometer working gas and data normalization procedures, that can potentially be up to 0.6°C–5.8°C (Saenger et al., 2021). While the choice of 17 O correction parameters yields negligible differences in the slopes and intercepts of the otolith Δ 47 ‐ T calibrations (anchored to ETH standards), the use of the accurate Δ 17 O values of these and other commercial standards (Fosu et al., 2020; Saenger et al., 2021; Wostbrock et al., 2020) may improve the agreement between inter‐laboratory calibrations and the overall accuracy of Δ 47 measurements.…”