Synthetic Witherite for Standardisation of Clumped Isotope (Δ47) Measurements

Abstract

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.