High-precision isotope measurements of H216O, H217O, H218O, and the Δ 17O-anomaly of water vapor in the southern lowermost stratosphere

[摘要] We report the first high-precision measurements of δ ¹⁸O and Δ ¹⁷O at highsouthern latitudes that can resolve changes in the isotopic composition ofwater vapor in the lowermost stratosphere and upper troposphere. A strongincrease of δ ¹⁸O with decreasing mixing ratio above the tropopause isevident in the data. Since also the water vapor mixing ratio decreases abovethe tropopause, the effect seen in the isotope data can be explained bymixing of moist air from the tropopause with dry stratospheric air. However,the source of this dry stratospheric air is not known; both fast transportfrom the extratropical tropopause or mixing with air from the dehydratedpolar vortex are likely. The magnitude of the Δ ¹⁷O-anomaly (departure frommass-dependent fractionation (MDF)) was below 2 per mil for each datapoint,and a zero anomaly in lower level stratospheric water vapor is possible.Various transport histories for the stratospheric data are discussed based onthe mixing ratio and isotope data.

[学科分类] 大气科学