Meromictic lake

A lake whose deep and surface waters do not mix completely each year. Its persistent layers create a deep zone isolated from seasonal exchange with the atmosphere.

Lake stratification: The layering of lake water by differences in temperature or dissolved substances. Temperature and dissolved salts help maintain the lake’s persistent water layers.
Monimolimnion: The deepest layer of a meromictic lake, which remains largely unmixed with upper water. This is the persistent deep-water layer that distinguishes meromictic lakes.
Paleolimnology: The study of past environments using physical, chemical, and biological evidence preserved in lake sediments. Undisturbed deep sediments can preserve records of environmental change.
Lake Kivu: A large African lake between Rwanda and the Democratic Republic of the Congo, known for deep dissolved gases. Its stable deep layers contain methane and carbon dioxide beneath shallower water.
Euxinia: The condition of anoxic water containing free hydrogen sulfide. In some meromictic lakes, oxygen-free deep water accumulates sulfide.
Chemocline: A boundary in water where the concentration of dissolved chemicals changes sharply with depth. This sharp chemical boundary often separates oxygenated surface water from deep anoxic water.
Mixolimnion: The upper layer of a meromictic lake that mixes with the atmosphere and may overturn seasonally. Seasonal mixing occurs here without reaching the monimolimnion.
Varve: An annual sediment layer, often formed by seasonal changes in sediment supply or composition. Some meromictic lakes preserve finely layered sediments that can be counted and analyzed.
Lake Nyos: A crater lake in Cameroon whose deep water released a lethal carbon dioxide cloud in 1986. Its stratified deep water accumulated gas until a sudden overturn released it.
Sulfate reduction: A microbial process that uses sulfate as an electron acceptor and produces sulfide. It can generate the hydrogen sulfide found in anoxic deep layers.

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