Question

What is a thermocline?

Answer 1

Hey mate!
A thermocline is a layer of water between a warmer layer above and a cooler layer below which has a more rapid rate of decline of temperature than either of the layers of its surroundings.
Hope it helps!

Answer 2

A thermocline is the transition layer between warmer mixed water at the ocean's surface and cooler deep water below. ... In the thermocline, temperature decreases rapidly from the mixed upper layer of the ocean (called the epipelagic zone) to much colder deep water in the thermocline (mesopelagic zone).