Thermocline

The thermocline (sometimes metalimnion) is a layer within a body of water where the temperature changes rapidly with depth.

Related Topics:
Water - Temperature

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Because water is not perfectly transparent, almost all sunlight is absorbed in the surface layer, which heats up. Wind and waves circulate the water in the surface layer, distributing heat within it somewhat, and the temperature may be quite uniform for the first few hundred feet.

Related Topics:
Surface layer - Wind - Waves

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Below this, however, the temperature drops very rapidly—perhaps 20 degrees Celsius with an additional 500 feet (150 m) of depth. This area of rapid transition is the thermocline.

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Below the thermocline, the temperature continues to drop with depth, but far more gradually. In the Earth's oceans, 90% of the water is below the thermocline. This deep ocean consists of layers of equal density, being poorly mixed, and may be as cold as 0 to 3 °C.

Related Topics:
Oceans - Deep ocean - Density

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The thermocline has been important in submarine warfare, because it can reflect active sonar.

Related Topics:
Submarine - Sonar

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When scuba diving, a thermocline of a few degrees Celsius can often be seen between two bodies of water, for example a colder upwelling or current running into a surface layer of warmer water. It gives the water an appearance of the wrinkled glass that is often used to obscure bathroom windows.

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