title: Choice of17O correction affects clumped isotope (Δ47) values of CO2measured with mass spectrometry.
abstract: BACKGROUND
  The clumped isotope composition of CO2(Δ47) derived from carbonate is widely used as a paleotemperature proxy with broad applications in geoscience. Its accuracy is, however, limited by inter-laboratory discrepancies of reference materials and disagreement among carbonate geothermometer calibrations. Here we show how the correction for the abundance of17O influences these discrepancies.
  
  
  METHODS
  We used CO2-H2O equilibration at known temperatures and phosphoric acid digested carbonates to generate CO2samples with a wide range in13C and18O compositions. All samples were purified using an offline vacuum line. We used a Thermo MAT 253 isotope ratio mass spectrometer with a Faraday collector array for m/z 44-49, to measure δ13C, δ18O, δ47, and Δ47values. Data were compiled using a traditional correction ('Santrock') for the17O interference in m/z 45 as well as a more recently proposed correction ('Brand') for17O interference. Two reference frames using CO2with distinct13C compositions were constructed to simulate an inter-laboratory comparison.
  
  
  RESULTS
  The traditional Santrock17O correction leads to a simulated Δ47inter-laboratory comparison offset of 0.06 ‰, and a 0.1 ‰ Δ47range in CO2-H2O 23°C equilibrations that is dependent on the13C composition. The more recent Brand17O correction removes these discrepancies. The traditional17O correction yields distinct temperature-Δ47calibration curves for synthetic carbonates precipitated using different methods to degas CO2, while the more recent17O correction collapses all calibration data onto a single curve.
  
  
  CONCLUSIONS
  The17O correction strategy employed by CO2and carbonate clumped-isotope researchers can have a large effect on the accuracy of Δ47values. Use of the traditional17O correction may have caused errors in published studies as large as 0.1 ‰ and may account for Δ47differences among laboratories and disagreement among previously published carbonate clumped isotope thermometry calibrations. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: IsoLab, Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Schauer
authors.affiliation: IsoLab, Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA.
authors.forename: Julia
authors.initials: J
authors.lastname: Kelson
authors.affiliation: IsoLab, Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA.|JISAO, University of Washington, Seattle, WA, USA.
authors.forename: Casey
authors.initials: C
authors.lastname: Saenger
authors.affiliation: IsoLab, Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA.
authors.forename: Katharine W
authors.initials: KW
authors.lastname: Huntington