Noun
A boundary layer in a body of water between areas of different temperature or salinity.
The bay has fresher water at the surface and saltier water at the bottom, in between is the pycnocline.
A layer of water where the density changes rapidly with depth
Source: en.wiktionary.orgBelow the pycnocline is the Deep Water mass, where salinity increases to 22.3 psu and temperatures rise to around 8.9 °C. Source: Internet
The base of the CIL is marked by a major pycnocline at about convert and this density disparity is the major mechanism for isolation of the deep water. Source: Internet