In situ observations of small-scale dynamics and compositional structure in the tropopause region are presented. The measurements were made aboard the Grob Egrett high-altitude research aircraft above Aberystwyth, Wales, in the summer of 2000. The observations presented here show evidence of mixing of ozone and water vapor in a patch of intense turbulence just above the tropopause. This turbulence is shown to be the result of wind shear above a tropospheric jet stream. The value of the vertical eddy diffusion coefficient in this turbulence is estimated to be 0.9 m2 s-1. It is also shown that wavelike perturbations superimposed on the overall tracer structure can be accounted for by a gravity wave.