On atmospheric loss of oxygen ions from earth through magnetospheric processes.
In Earth's environment, the observed polar outflow rate for O(+) ions, the main source of oxygen above gravitational escape energy, corresponds to the loss of approximately 18% of the present-day atmospheric oxygen over 3 billion years. However, part of this apparent loss can actually be returned to the atmosphere. Examining loss rates of four escape routes with high-altitude spacecraft observations, we show that the total oxygen loss rate inferred from current knowledge is about one order of magnitude smaller than the polar O(+) outflow rate. This disagreement suggests that there may be a substantial return flux from the magnetosphere to the low-latitude ionosphere. Then the net oxygen loss over 3 billion years drops to approximately 2% of the current atmospheric oxygen content.
Department of Earth and Planetary Sciences, University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan. seki@space.eps.s.u-tokyo.ac.jp
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