The Thermocline Is Located at the Base of the Epipelagic Zone.

The thermocline is a transitional layer located at the base of the ocean’s Epipelagic Zone (the uppermost layer that’s closest to the surface). It marks a transition between the warmer water at the surface (which gets heated by the sunlight and mixed by the wind) and the colder, deeper water below. In the thermocline, water temperature decreases rapidly. The depth and strength of the thermocline varies seasonally, yearly, and geographically.