Paired carbonate standard clumped isotope (Δ47 and Δ48) values on the absolute reference frame using equilibrated gas and carbonate standard-based transfer functions

Abstract:

The clumped isotope (Δ₄₇) thermometer, based on the mass spectrometric measurement of mass 47 CO₂ isotopologues, is a tool that is growing in use throughout many areas of the geosciences. Here we take advantage of newly developed analytical resolving power for the measurement of the primary mass 48 CO₂ isotopologue (¹²C¹⁸O¹⁸O) and report carbonate standard values determined over a three-year interval for >10 standards against equilibrated gases, which lays the foundation for accurate determination of paired Δ₄₇ and Δ₄₈ values on an absolute reference frame using both equilibrated gas and carbonate standard-based transfer functions. Due to the extremely low abundance of mass 48 CO₂ isotopologues, the development of robust standard values for Δ₄₈ will be critical in ensuring accurate determination of unknown sample Δ₄₈ values. We also report mixing experiment data and non-linear mixing model calculations for Δ₄₈ and Δ₄₇ vs Δ₄₈ for samples with varying bulk isotope (δ¹⁸O and δ¹³C) values.