CONTINUOUS, HIGH-RESOLUTION MEASUREMENTS OF Δ17O OF H2O

The measurement of Δ¹⁷O, the deviation in δ¹⁷O from the global meteoric water line, ln(δ¹⁷O+1) – 0.528ln(δ¹⁸O+1), offers considerable potential for separating the various influences on water isotope variations recorded in polar ice cores. The availability of Δ¹⁷O measurements has been limited by the time-consuming nature of analysis by isotope-ratio mass spectrometery (IRMS) method, which requires conversion of H₂O to O₂ by flourination. Laser spectroscopy has made it possible to measure Δ¹⁷O without the flourination step. Such measurements remain challenging because existing instruments are subject to calibration drift and sample-to-sample memory. Nevertheless, when careful protocols are followed, reliable and routine measurements can be achieved, competitive with IRMS. Furthermore, laser spectroscopy instruments can be coupled with continuous flow analysis (CFA) systems to provide very-high-resolution ice core measurements. Here, we show the first continuous record of Δ¹⁷O ever obtained from an ice core. We coupled a CFA system with a Picarro L214Oi instrument to analyze a 1750-m long ice core from the South Pole, with sub- centimeter resolution for δ¹⁷O, δ¹⁸O and δD. Data averaging yields an effective resolution for Δ¹⁷O of 50 cm, with better than 10 per meg precison.