Equilibrated Gas and Carbonate Standard‐Derived Dual (Δ47 and Δ48) Clumped Isotope Values. (21st February 2023)

• Record Type: Journal Article
• Authors: Lucarelli, Jamie K.; Carroll, Hannah M.; Ulrich, Robert N.; Elliott, Ben M.; Coplen, Tyler B.; Eagle, Robert A.; Tripati, Aradhna
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 24:Number 2(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-21
• Subjects: clumped isotopes -- stable isotopes -- equilibrium -- mass spectrometry -- paleoclimate -- geochemistry; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2022GC010458
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Carbonate clumped isotope geochemistry has primarily focused on mass spectrometric determination of m/z 47 CO2 for geothermometry, but theoretical calculations and recent experiments indicate paired analysis of the m/z 47 ( 13 C 18 O 16 O) and m/z 48 ( 12 C 18 O 18 O) isotopologues (referred to as Δ47 and Δ48 ) can be used to study non‐equilibrium isotope fractionations and refine temperature estimates. We utilize 5, 448 Δ47 and 3, 400 Δ48 replicate measurements of carbonate samples and standards, and 183 Δ47 and 195 Δ48 replicate measurements of gas standards from 2015 to 2021 from a multi‐year and multi‐instrument data set to constrain Δ47 and Δ48 values for 27 samples and standards, including Devils Hole cave calcite, and study equilibrium Δ47 ‐Δ48, Δ47 ‐temperature, and Δ48 ‐temperature relationships. We compare results to previously published findings and calculate equilibrium regressions based on data from multiple laboratories. We report acid digestion fractionation factors, Δ*63‐47 and Δ*64‐48, and account for their dependence on the initial clumped isotope values of the mineral. Plain Language Summary: A powerful tool for reconstructing past temperatures is based on the extent of carbonate ions in carbonate minerals with more than one heavy isotope substitution, termed carbonate clumped isotope thermometry. The use of the clumped isotope thermometer assumes that the mineral formed under isotopic equilibrium conditions, however, some carbonate minerals do not form at equilibrium. When carbonate minerals do not form at isotopic equilibrium, they are typically not useful for temperature reconstructions. It is now possible to simultaneously determine the extent of heavy isotope substitution in mass 47 and mass 48 CO2 isotopologues from carbonate minerals precipitated at equilibrium. This relationship is useful to identify kinetic effects in sample measurements and recover formation temperature. Here, we use experimental measurements and theory to constrain the equilibrium relationships between heavy isotope substitution in mass 47 and mass 48 CO2 isotopologues, and their relationships to formation temperature. Key Points: Reproducible Δ47 and Δ48 values were determined for 27 samples and standards Equilibrium dual clumped isotope relationships and compositionally dependent acid fractionation factors were determined