ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-2949-2005 High-precision isotope measurements of H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>17</sup>O, H<sub>2</sub><sup>18</sup>O, and the &Delta; <sup>17</sup>O-anomaly of water vapor in the southern lowermost stratosphere Franz P. 1 Röckmann T. 1 Max-Planck-Institute for Nuclear Physics, Heidelberg, Germany 07 11 2005 5 11 2949 2959 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/5/2949/2005/acp-5-2949-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/2949/2005/acp-5-2949-2005.pdf

We report the first high-precision measurements of &delta; <sup>18</sup>O and &Delta; <sup>17</sup>O at high southern latitudes that can resolve changes in the isotopic composition of water vapor in the lowermost stratosphere and upper troposphere. A strong increase of &delta; <sup>18</sup>O with decreasing mixing ratio above the tropopause is evident in the data. Since also the water vapor mixing ratio decreases above the tropopause, the effect seen in the isotope data can be explained by mixing of moist air from the tropopause with dry stratospheric air. However, the source of this dry stratospheric air is not known; both fast transport from the extratropical tropopause or mixing with air from the dehydrated polar vortex are likely. The magnitude of the &Delta; <sup>17</sup>O-anomaly (departure from mass-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 on the mixing ratio and isotope data.