Microstructure observations over the Black Sea shelf and slope north of the Bosphorus reveal a very small turbulent diapycnal diffusivity, K&rgr;≈10-6 m2s-1 in the Cold Intermediate Water during late summer, when winds are at their seasonal minimum. Recent modeling by Ogˇuz et al. [1998> shows that only with such low diffusivity can the observed separation between dissolved oxygen, O2, and hydrogen sulfide, H2S, be maintained. The measurements also provide a reference for mixing over continental shelves where tides are negligible and when winds are light. ¿ 1999 American Geophysical Union