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

Abstract

that is analyzed by dual-inlet isotope ratio mass spectrometry (IRMS). We describe a new laser spectroscopy instrument for highprecision 17 O measurements. The new instrument uses cavity ring-down spectroscopy (CRDS) with laser-currenttuned 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 17 O using integration times of less than 30 min. Calibration with respect to accepted water standards demonstrates that both the precision and the accuracy of 17 O are competitive with conventional IRMS methods. The new instrument also achieves simultaneous analysis of δ 18 O, δ 17 O and δD with precision of < 0.03 ‰, < 0.02 and < 0.2 ‰, respectively, based on repeated calibrated measurements.

Water vapor δ2H, δ18O and δ17O measurements using an off‐axis integrated cavity output spectrometer – sensitivity to water vapor concentration, delta value and averaging‐time

“…Recently, there has been growing interest in a new hydrological tracer δ 17 O, accompanied by the development of high-precision analytical methods [9,10] . Similar to δ 2 H and δ 18 O, δ 17 O can be used to infer the degree of isotope enrichment during transpiration [11] , serve as tracer in different water bodies (e.g., meteoric water and ice cores) [12][13][14] , and characterize evaporative regimes.…”

“…First, in order to study the temporal and spatial dynamics of water vapor δ 17 O values in field settings where different water vapor concentrations and various delta values often occur, we need to evaluate the accuracy and precision of laser-based instruments in complex and volatile environments. Second, in previous observations, the trends in accuracy and precision of δ 2 H and δ 18 O measurements with increasing water vapor concentrations were different for different measuring techniques and instruments [10,[23][24][25] , and even for the same sample for different isotopes [23,25] . Third, the fundamental principle of LAS techniques (e.g., OA-ICOS and CRDS techniques) is measuring the mixing ratio of different isotopes.…”

“…They showed that the OA-ICOS technique, which is energy efficient and requires no sample conversion, can measure δ 2 H, δ 18 O and δ 17 O values with a precision comparable to the IRMS technique. Later, Steig et al [10] measured the same standard (GISP) using the Cavity Ring Down Spectroscopy (CRDS) technique, demonstrating that this instrument could also measure δ 17 O values with high precision. While the results of that study were encouraging, the CRDS technique requires high power and dry air or N2 as carrier gas, potentially making remote deployment difficult.…”

“…In addition, the technique requires water to be converted to O2 rather than CO2 or CO, which is a laborious process [19][20][21] . As a result, δ 17 O measurements derived from the IRMS technique are complicated, expensive and timeconsuming, and can only be done in a small number (< 10) of laboratories worldwide [9,10,21,22] .…”

“…In order to utilize δ [23,24] , delta range [9,26] and averaging-time [10,27] ) on instrument performance will improve our capacity to interpret observations of δ 2 H, δ 18 O and δ 17 O from complex environments.…”