Diffusive convection

From Glossary of Meteorology

diffusive convection

A form of double-diffusive convection that occurs when cold freshwater overlies warm salty water.

If a parcel of warm and salty water is moved upward in the water column, it loses heat more quickly than it loses salt, becoming colder and saltier, and thus denser, than its environs, or than the water at its initial position. It then sinks beyond its initial position into water that is saltier but warmer. It then gains heat from this water and begins to rise past its initial position. Diffusive convection transports heat more efficiently than salt and is believed to be responsible for staircase- like structures observed in the arctic thermocline.
See also double diffusive convection, Turner angle.