Noble gases natural occurrence

The occurrence of thermal diffusion in nature was first observed by Severinghaus et al. (1996) for soil gas in sand dunes. The fractionation of soil air by water vapor diffusion, gravitational settling, and thermal diffusion studied by these authors may also have a small effect on dissolved noble gases in ground water, and hence the calculation of noble gas paleotemperatures. However, these comparatively minor effects have not yet been further studied in the soil-air-ground-water system. 

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