Calibrated high-precision ¹⁷O-excess measurements using cavity ring-down spectroscopy with laser-current-tuned cavity resonance

• Main Authors: E. J. Steig, V. Gkinis, A. J. Schauer, S. W. Schoenemann, K. Samek, J. Hoffnagle, K. J. Dennis, S. M. Tan
• Format: Article
• Language: English
• Published: Copernicus Publications 2014-08-01
• Series: Atmospheric Measurement Techniques
• Online Access: http://www.atmos-meas-tech.net/7/2421/2014/amt-7-2421-2014.pdf

High-precision analysis of the ¹⁷O / ¹⁶O isotope ratio in water and water vapor is of interest in hydrological, paleoclimate, and atmospheric science applications. Of specific interest is the parameter ¹⁷O excess (&Delta;¹⁷O), a measure of the deviation from a~linear relationship between ¹⁷O / ¹⁶O and ¹⁸O / ¹⁶O ratios. Conventional analyses of &Delta;¹⁷O of water are obtained by fluorination of H₂O to O₂ that is analyzed by dual-inlet isotope ratio mass spectrometry (IRMS). We describe a new laser spectroscopy instrument for high-precision &Delta;¹⁷O measurements. The new instrument uses cavity ring-down spectroscopy (CRDS) with laser-current-tuned cavity resonance to achieve reduced measurement drift compared with previous-generation instruments. Liquid water and water-vapor samples can be analyzed with a better than 8 per meg precision for &Delta;¹⁷O using integration times of less than 30 min. Calibration with respect to accepted water standards demonstrates that both the precision and the accuracy of &Delta;¹⁷O are competitive with conventional IRMS methods. The new instrument also achieves simultaneous analysis of δ¹⁸O, &Delta;¹⁷O and &delta;<i>D</i> with precision of < 0.03&permil;, < 0.02 and < 0.2&permil;, respectively, based on repeated calibrated measurements.