Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 4 2005 10.5194/acpd-5-5373-2005 http://www.atmos-chem-phys-discuss.net/5/5373/2005/ http://www.atmos-chem-phys-discuss.net/5/5373/2005/acpd-5-5373-2005.html http://www.atmos-chem-phys-discuss.net/5/5373/2005/acpd-5-5373-2005.pdf 5373 5403 2005-07-28 High-precision isotope measurements of H₂¹⁶, H₂¹⁷, H₂¹⁸, and the Δ¹⁷O-anomaly of water vapor in the southern lowermost stratosphere P. Franz T. Röckmann Max-Planck-Institute for Nuclear Physics, Heidelberg, Germany now at: Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands We report the first high-precision measurements of δ¹⁸O and Δ¹⁷O 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 δ¹⁸O with decreasing mixing ratio above the tropopause is found. Since also the water vapor mixing ratio decreases above the tropopause, the isotope data can be explained by mixing of relatively moist air from the tropopause with dry stratospheric air. However, the nature of dehyration process that produced this dry stratospheric, e.g., fast transport from the extratropical tropopause or mixing with air from the dehydrated polar vortex, cannot be clearly identified. The magnitude of the Δ¹⁷O-anomaly (departure from mass-dependent fractionation (MDF)) was below 2 for each datapoint, and the mean is consistent with a zero anomaly in lower level stratospheric water vapor. Various transport histories for the stratospheric data are discussed based on the mixing ratio and isotope data.