Using high-precision measurements of the isotopic ratios of N2, O2, and Ar, as well as the mole fraction of Ar, S. Ishidoya and co-authors show that gravitational separation occurs in the stratosphere below the turbopause. Observed vertical profiles agree well with those expected theoretically from molecular mass differences. Simulations with a 2D model of the middle atmosphere indicate that a relationship between gravitational separation and stratospheric age-of-air would be significantly affected if the Brewer Dobson Circulation was enhanced. Therefore they suggest that gravitational separation could serve as a new indicator of changes in stratospheric circulation. The full abstract can be found here.