Carbonate clumped isotope analysis (Δ47) of 21 carbonate standards determined via gas source isotope ratio mass spectrometry on four instrumental configurations using carbonate-based standardization and multi-year datasets

Rationale: Clumped isotope geochemistry examines the pairing or clumping of rare, heavy isotopes in molecules and provides information about the thermodynamic and kinetic controls on their formation. Since clumped isotope measurements of carbonate minerals were first published 15 years ago, interlaboratory offsets in calibrations have been observed, and laboratory and community practices for measurement, data analysis, and instrumentation have evolved. Here we briefly review historical and recent developments for carbonate clumped isotope measurements, test a recently published proposal for carbonate-based standardization on multiple instruments using multi-year datasets, and report values for 21 different carbonate standards that allows for recalculations of previously published datasets. Methods: We examine data from 4628 standards analyzed over a 4 year interval on Thermo MAT 253 and Nu Perspective IS mass spectrometers, using common acid bath and small sample individual reaction vessels. Each configuration was analyzed by treating some standards as working standards and the remainder as unknowns (consistency standards). Results: We show that acid digestion systems using either individual reaction vessels at 70°C or a common acid bath at 90°C, as well as different mass spectrometer models, yield indistinguishable results when instrument drift is well characterized. For the linearity correction, the implementation of mixed gas- and-carbonate standardization or carbonate-only standardization yield similar results. No difference is seen in the use of either 3 or 8 working standards for the construction of transfer functions. Conclusions: We expanded the number of instrumental configurations utilized for intercomparison beyond prior work, and show all configurations yield similar reproducibility if instrument drift is robustly characterized and either carbonate- or mixed gas-and-carbonate-based standardization is used. Δ47 values are reported for 21 carbonate standards, facilitating the intercomparison of data from a diversity of labs and instrument configurations, and the restandardization of a broad range of sample sets generated between 2006 to present.