Pycnocline

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A pycnocline is a cline caused by a strong, vertical density gradient within a body of water. In freshwater environments such as lakes this density change is primarily caused by water temperature (thermocline), while in seawater environments such as oceans and estuaries, the rapid density change in the water column is often caused by a combination of decreasing water temperature and increasing salinity (halocline).

Areas where freshwater and saltwater environments meet, such as bays and near river mouths, often have strong, well defined pycnoclines. A large amount of run off from land of warmer freshwater can float upon colder saltwater entering an estuary forming a salt wedge. The amount of mixing from top to bottom will determine the stratification or strength of the pycnocline. With little mixing from the friction of currents, the density differences between the fresh and salt water dominate.

Pycnoclines tend to disappear in the open ocean at around 50 or 60 degrees North or South Latitude. This is due to lowered salinity and temperature change near the poles.

Types of clines

• Thermocline - A cline based on difference in water temperature,
• Chemocline - A cline based on difference in water chemistry,
• Halocline - A cline based on difference in water salinity.

See also

• Isopycnal

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