Vertical profiles of the O2/N2 ratio in the stratosphere over Japan and Antarctica

Abstract

To examine the spatial and temporal behavior of stratospheric O2, air samples were collected using a cryogenic sampler over Sanriku, Japan and Syowa, Antarctica and analyzed for δ(O2/N2), δ15N of N2 and δ18O of O2. The measured values of all these components decreased gradually with height. The differences in δ(O2/N2), δ15N and δ18O between the middle and lowermost levels of the stratosphere were about 250, 100, and 180 per meg, respectively. The observed stratospheric profiles of δ15N and δ18O were in agreement with those calculated using a steady‐state 1‐dimensional eddy‐diffusion/molecular‐diffusion model, which suggests that the upward decrease of stratospheric δ(O2/N2) is caused by a gravitational separation of O2 and N2 molecules. The averaged stratospheric δ(O2/N2) at heights above 20–25 km over Sanriku, corrected for the gravitational separation, was always higher than the upper tropospheric δ(O2/N2) value over Japan, and it decreased secularly. From the past temporal δ(O2/N2) variation deduced from the gravitational separation‐corrected stratospheric δ(O2/N2) values and the mean ages of the respective air samples, which corresponds to its secular trend in the troposphere, average terrestrial biospheric and oceanic CO2 uptake for October 1993–September 2001 were estimated to be 1.1 ± 1.3 and 1.8 ± 1.3 GtC yr−1, respectively.