Equilibrated gas and carbonate standard-derived paired clumped isotope (Δ47 and Δ48) values on the absolute reference frame

Abstract

Rationale: Carbonate clumped isotope geochemistry has primarily focused on mass spectrometric determination of mass-47 CO 2 for geothermometry, but theoretical calculations indicate paired analysis of the mass-47 ( 13 C-18 O-16 O) and mass-48 ( 12 C-18 O-18 O) isotopologues (denoted with Δ 47 and Δ 48 notation) can be used to study nonequilibrium isotope fractionations and refine temperature estimates. We are one of two labs currently utilizing paired Δ 47 and Δ 48 measurements to study equilibrium and kinetic isotope effects in carbonates. Additional work is needed on different instruments to define standard Δ 48 values against equilibrated gases and evaluate Δ 48 values using carbonate transfer functions. Methods: We determined Δ 47 and Δ 48 of standards using isotope ratio mass spectrometry during the time interval of 2015-2021 on a Thermo Fischer MAT 253 mass spectrometer with a common acid bath digestion system and two Nu Instruments Perspective mass spectrometers with common acid bath and individual reaction vessel digestion systems. A total of 5,581 Δ 47 and 4,212 Δ 48 measurements of carbonates, and 183 Δ 47 and 195 Δ 48 measurements of gas standards are used from robust correction intervals over multiple years. We report statistical methods for data screening and quality assurance.

Paired Δ47 and Δ48 analyses and model calculations constrain equilibrium, experimentally-manipulated kinetic isotope effects, and mixing effects in calcite

“…The instruments used in this work were a Thermo Fisher MAT 253, and two Nu Instruments Perspective mass spectrometers, with both Nu Instruments having multiple configurations (Table 2). All instrumental configurations used here have been shown to produce statistically indistinguishable Δ47 (Upadhyay et al, 2021;Lucarelli et al, 2021) and the Nu Instruments produce statistically indistinguishable Δ48 data (Lucarelli et al, 2021). Only data from the Nu Instruments are used in the Δ48 analyses reported here.…”

“…Δ47 data are presented relative to international standards ETH-1, ETH-2, ETH-3 in the I-CDES reference frame (Bernasconi et al, 2021) at 90 o C, Δ47 I-CDES. Δ48 data are presented relative to the same carbonate standards, with the addition of the in-house carbonate standard, Veinstrom (Upadhyay et al, 2021;Lucarelli et al, 2021), in the 90 o C reference frame, Δ48 CDES 90.…”

“…Measured Δ47 and Δ48 were converted to theoretical calcite mineral Δ63 and Δ64, respectively, for direct comparison to model predictions for kinetic and equilibrium relationships between bulk and clumped isotopes. This conversion was carried out using equations from Lucarelli et al (2021). In summary, regressions were determined for compositionally dependent acid digestion fractionation factors (AFFs), Δ*63-47 and Δ*64-48, by using model predicted Δ63 and Δ64 values for calcite precipitated at 600 o C and 33.7 o C (Hill et al, 2014;Tripati et al, 2015).…”

“…The use of Δ47 and Δ48 as paleothermometers rely on equilibrium clumped isotope fractionation in the carbonate mineral lattice. However, recent theoretical and experimental work has shown that some biogenic and abiogenic carbonates yield disequilibrium Δ47 (Ghosh et al, 2006;Daëron et al, 2011, Saenger et al, 2012, Tang et al, 2014Tripati et al, 2015;Guo et al, 2019;Daeron et al, 2019) and Δ48 values (Tripati et al, 2015;Guo, 2020;Bajnai et al, 2020;Lucarelli et al, 2021;Fiebig et al, 2021).…”

“…The paired measurement of Δ47 and Δ48 has been theoretically (Hill et al, 2014;Tripati et al, 2015;Guo, 2020;Hill et al, 2020) and experimentally (Fiebig et al, 2019;Bajnai et al, 2020;Lucarelli et al, 2021;Fiebig et al, 2021) shown to have a characteristic equilibrium relationship. The equilibrium Δ47-Δ48 relationship along with constrained boundaries of disequilibrium trajectories in dissolved inorganic carbon (DIC) pools and in carbonate minerals may be used to identify the origin of kinetic isotope effects (Tripati et al, 2015;Bajnai et al, 2020;Guo, 2020) and used to correct for such effects and derive expected equilibrium clumped isotope values from samples Guo, 2020).…”