RESUMEN
RATIONALE: 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 of 17 O influences these discrepancies. METHODS: We used CO2 -H2 O equilibration at known temperatures and phosphoric acid digested carbonates to generate CO2 samples with a wide range in 13 C and 18 O 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 δ13 C, δ18 O, δ47 , and Δ47 values. Data were compiled using a traditional correction ('Santrock') for the 17 O interference in m/z 45 as well as a more recently proposed correction ('Brand') for 17 O interference. Two reference frames using CO2 with distinct 13 C compositions were constructed to simulate an inter-laboratory comparison. RESULTS: The traditional Santrock 17 O correction leads to a simulated Δ47 inter-laboratory comparison offset of 0.06 , and a 0.1 Δ47 range in CO2 -H2 O 23°C equilibrations that is dependent on the 13 C composition. The more recent Brand 17 O correction removes these discrepancies. The traditional 17 O correction yields distinct temperature-Δ47 calibration curves for synthetic carbonates precipitated using different methods to degas CO2 , while the more recent 17 O correction collapses all calibration data onto a single curve. CONCLUSIONS: The 17 O correction strategy employed by CO2 and carbonate clumped-isotope researchers can have a large effect on the accuracy of Δ47 values. Use of the traditional 17 O correction may have caused errors in published studies as large as 0.1 and may account for Δ47 differences among laboratories and disagreement among previously published carbonate clumped isotope thermometry calibrations. Copyright © 2016 John Wiley & Sons, Ltd.