Balancing precision and throughput of O and Δ'O analysis of natural waters by Cavity Ringdown Spectroscopy.

O and Δ'O are emerging tracers increasingly used in isotope hydrology, climatology, and biochemistry. Differentiating small relative abundance changes in the rare O isotope from the strong covariance with O imposes ultra-high precision requirements for this isotope analysis. Measurements of O by Cavity Ringdown Spectroscopy (CRDS) are attractive due to the ease of sample preparation, automated throughput, and avoidance of chemical conversions needed for isotope-ratio mass spectrometry. However, the CRDS approach requires trade-offs in measurement precision and uncertainty. In this protocol document, we present the following:•New analytical procedures and a software tool for conducting O and Δ'O measurements by CRDS.•Outline a robust uncertainty framework for Δ'O determinations.•Description of a CRDS performance framework for optimizing throughput, instrumental stability, and Δ'O measurement precision and accuracy.