Rapid and precise measurement of carbonate clumped isotopes using laser spectroscopy

Carbonate clumped isotope abundance is an important paleothermometer, but measurement is difficult, slow, and subject to cardinal mass (m/z) interferences using isotope ratio mass spectrometry (IRMS). Here, we describe an optical spectroscopic measurement of carbonate clumped isotopes. We have adapted a tunable infrared laser differential absorption spectrometer (TILDAS) system to measure the abundances of four CO2 isotopologues used for clumped isotope thermometry. TILDAS achieves the same precision (0.01% SE) as IRMS measurements rapidly (similar to 50 min per carbonate analysis) and using small samples (<2 mg of calcite), without making assumptions about 17O abundance in the sample. A temperature calibration based on 406 analyses of CO2 produced by digestion of 51 synthetic carbonates equilibrated at 6 degrees to 1100 degrees C is consistent with results for natural carbonates and previous calibrations. Our system results were indistinguishable from IRMS systems after replicating the InterCarb interlaboratory calibration. Measurement by TILDAS could change the landscape for clumped isotope analysis.

Automated summary

This study presents an optical spectroscopic method for measuring carbonate clumped isotopes. The method utilizes a TILDAS system which enables rapid and precise measurement of CO2 isotopologue abundances without assuming 17O abundance. The results from the TILDAS system are consistent with IRMS measurements after calibration. This measurement method has the potential to revolutionize clumped isotope analysis.