Pycnocline

From Glossary of Meteorology



pycnocline

A vertical density gradient (as determined by the vertical temperature and salinity gradients and equation of state) in some layer of a body of water, which is appreciably greater than the gradients above and below it; also a layer in which such a gradient occurs.

The principal pycnoclines in the ocean are either seasonal, due to heating of the surface water in summer or freshwater inputs, or permanent.