The thermocline is a layer of water in the twilight zone of the ocean where the water temperature drops really quickly. The sun’s light and warmth keep the sunlight zone pretty warm, and the wind and waves mix that warmth to a certain depth, around 330 feet (100 meters). But below the sunlight zone the water temperature starts dropping quickly. The temperature difference from the top of the thermocline to the bottom can be as great as almost 60 degrees Fahrenheit (about 20 degrees Celsius). Below about 1,000 feet (300 meters), the ocean temperatures stay pretty much the same.View More what is the meaning of Thermocline?