Microstructure and hydrographic observations, during September 2007 in the boundary current on the East Siberian continental slope, document upper ocean stratification and along-stream water mass changes. A thin warm surface layer overrides a shallow halocline characterized by a ∼40-m thick temperature minimum layer beginning at ∼30 m depth. Below the halocline, well-defined thermohaline diffusive staircases extended downwards to warm Atlantic Water intrusions found at 200–800 m depth. Observed turbulent eddy kinetic energy dissipations are extremely low ( < 10⁻⁶ W m⁻³), such that double diffusive convection dominates the vertical mixing in the upper-ocean. The diffusive convection heat fluxes F _H ^dc ∼1 W m⁻², are an order of magnitude too small to account for the observed along-stream cooling of the boundary current. Our results implicate circulation patterns and the influence of shelf waters in the evolution of the boundary current waters.