Oxygen isotope anomaly not present in water vapor from Alert, Canada

Lin et al. (1) claim to have discovered a positive 17O anomaly in water vapor from Alert, Canada, indicative of a component of stratospheric origin. However, their data (Tables S1−S5) do not support that assertion. Their finding of Δ17O = 76 ± 16 ppm (2 SE) in the Alert samples is relative to a reference fractionation line [designated Chicago local precipitation (CLP)] of much lower precision [slope 0.529 ± 0.003, ordinate axis intercept 70 ± 33 ppm from Vienna Standard Mean Ocean Water (VSMOW) on the logarithmic form of the oxygen triple-isotope plot] than is the norm for investigations that characterize Δ17O values at the parts per million …