Synthetic Witherite for Standardisation of Clumped Isotope (Δ47) Measurements

Carbonate clumped isotope, quantified by Δ₄₇ 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 Δ₄₇ 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 Δ₄₇ 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 Δ₄₇ values to agreed ETH carbonate values on the Intercarb-Carbon Dioxide Equilibrium Scale, the witherite reference materials can be used to determine Δ₄₇ values without using equilibrated gases and reduce the consumption of ETH carbonates.