Depth and temperature variation

The temperature of the ocean also varies from top to bottom, giving a vertical structure to most of the ocean. There is an upper layer of water, up to 200m deep, that is warmed by the Sun and has the same temperature from top to bottom. Below that is a layer called the thermocline, reaching down in places to 1000m, which is colder at the bottom than at the top. The deep ocean below the thermocline, making up 80% of the ocean, is the same very cold temperature throughout.

The ocean has 3 main temperature layers. The upper (warm) and deep (cold) layers have the same temperature throughout. Between is the thermocline, which is warmer at the top than the bottom.