1IsoLab, Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA
2Quaternary Research Center, University of Washington, Seattle, WA 98195, USA
3Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
4Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA
5Picarro Inc. Santa Clara, CA 95054, USA
Abstract. 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 17Oexcess, a measure of the deviation from a linear relationship between 17O/16O and 18O/16O ratios. Conventional analyses of 17Oexcess 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 17Oexcess measurements. The new instrument uses cavity ring-down spectroscopy (CRDS) with laser-current tuning to achieve reduced measurement drift compared with previous-generation instruments. Liquid water and water vapor samples can be analyzed with better than 8 per meg precision for 17Oexcess using integration times of less than 30 min. Calibration with respect to accepted water standards demonstrates that both the precision and the accuracy are competitive with conventional IRMS methods. The new instrument also achieves simultaneous measurements of δ18O, 17Oand δD with precision < 0.03‰, < 0.02‰ and < 0.2‰, respectively.