Oxygen Isotopic Exchange Between CO₂ and Phosphoric Acid: Implications for the Measurement of Clumped Isotopes in Carbonates

Abstract

Abstract Experiments have been conducted in which CO 2 gases with varying C and O isotopic compositions and with stochastic and nonstochastic Δ 47 values have been allowed to equilibrate with phosphoric acid of two concentrations in reaction vessels of varying dimensions at temperatures of 25 and 90 °C. Rates of 13 C 18 O and 18 O exchange between the CO 2 and the phosphoric acid varied as a function of the length of exposure, volume of reaction vessel, acid strength, and difference of the initial Δ 47 and δ 18 O values of the CO 2 from theoretical equilibrium values. The Δ 47 values were also altered by heated stainless steel surfaces such as those found within the Kiel device and other preparation systems. These results have been used to explain variations in the differences in the fractionation between 25 and 90 °C reported for calcite by different workers as well as differences in the slopes between temperature and Δ 47 values produced by reacting samples at different temperatures (25 and 90 °C).