Isotopic measurements (Δ17O and Δ18O) of CO2 along with concentration measurements of SF6, CCl3F (CFC-11), CCl2F2 (CFC-12) and CCl2FCClF2 (CFC-113) in stratospheric samples collected within the Arctic polar vortex are reported. These are the first simultaneous measurements of the concentration of fluorinated compounds and the complete oxygen isotopic composition of CO2 in the middle atmosphere. A mass-independent anomaly in the oxygen isotopic composition of CO2 is observed that arises from isotopic exchange with stratospheric O(1D) derived from O3 photolysis. The data exhibit a strong anti-correlation between the Δ17O (the degree of the mass-independent anomaly) and molecular tracer concentrations. The potential ability of this isotopic proxy to trace mesospheric and stratospheric transport is discussed. ¿ 2001 American Geophysical Union