Synthetic Witherite for Standardisation of Clumped Isotope (????????₄₇) Measurements

Carbonate clumped isotope, quantified by ?(47) value, has wide application potential in Earth science. A recently proposed carbonate standardisation scheme based on community-available reference materials (i.e., ETH-1-4) has proven to improve interlaboratory comparability in ?(47) measurement. However, the shortage of these reference materials may be problematic in future; therefore, developing traceable and supplementary in-house reference materials may become necessary, especially when supplies run out. Here, we describe a method of producing synthetic witherite carbonates with variable bulk isotopic compositions and clumped isotope ordering states, for which ?(47) values were determined together with ETH carbonate reference materials. Results indicate that the witherite carbonates allow effective corrections for instrumental linearity and scale variations, improving long-term reproducibility. Additionally, by normalising witherite ?(47) values to agreed ETH carbonate values on the Intercarb-Carbon Dioxide Equilibrium Scale, the witherite reference materials can be used to determine ?(47) values without using equilibrated gases and reduce the consumption of ETH carbonates.