Define these terms: thermocline, halocline, pycnocline

Thermocline - a steep temperature gradient in a body of water, that is marked by a layer above and below at which the water is at different temperatures.

halocline - a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water.

pycnocline - a layer in an ocean or other body of water in which water density increases rapidly with depth.