Comment on “Record of δ 18 O and 17 O‐excess in ice from Vostok Antarctica during the last 150,000 years” by Amaelle Landais et al.

[1] On the basis that oxygen triple-isotope fractionation resulting from water vapor diffusion in air should differ in magnitude from that associated with equilibrium evaporation and condensation, and with very low sensitivity to temperature, Angert et al. [2004] postulated that the regression line of ln(1 + dO) versus ln(1 + dO) for meteoric waters may be displaced by very small, positive shifts from the corresponding data points for oceanic waters. In turn, the magnitude of this ‘O-excess’ in meteoric waters should be controlled primarily by the relative humidity of the vapor source region. Barkan and Luz [2007] discussed this concept further and defined the magnitude of the offset as: