Clear Lake (also Clearwater Lake) is a marine lake located on
Eil Malk island in
Palau
Palau, officially the Republic of Palau, is an island country in the Micronesia subregion of Oceania in the western Pacific Ocean. The Republic of Palau consists of approximately 340 islands and is the western part of the Caroline Islands ...
. Eil Malk (also Mecherchar) is part of the
Rock Islands
The Rock Islands of Palau, also called ''Chelbacheb'', are a collection of several hundred small limestone or coral uprises in the Southern Lagoon of Palau between Koror and Peleliu, now an incorporated part of Koror State. There are between ...
, a group of small, rocky, mostly uninhabited islands in Palau's Southern Lagoon, between
Koror and
Peleliu. There are about 70 other
marine lakes located throughout the Rock Islands. Clear Lake is notable for endemic subspecies of golden jellyfish and is one of five marine lakes in Palau used for several scientific researches in
evolutionary biology
Evolutionary biology is the subfield of biology that studies the evolutionary processes such as natural selection, common descent, and speciation that produced the diversity of life on Earth. In the 1930s, the discipline of evolutionary biolo ...
, the other lakes being
Jellyfish Lake,
Goby Lake,
Uet era Ngermeuangel,
Uet era Ongael.
Golden jellyfish
Clear Lake is one of the oldest of
meromictic marine lakes in Palau and is circa 15,000 - 12,000 years old. It is connected to the ocean through fissures and tunnels in the limestone of ancient
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
reef. However the lake is sufficiently isolated and the conditions are different enough that the diversity of species in the lake is greatly reduced from the nearby lagoon. The
golden jellyfish ''Mastigias'' cf. ''papua salii'' and possibly other species in the lake have evolved to be substantially different from their close relatives living in the nearby
lagoons.
Lake stratification
Clear Lake is
stratified into two layers, an
oxygenated upper layer (mixolimnion) and a lower
anoxic
Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts:
* Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...
layer (monimolimnion). The
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
concentration in the lake declines from about 6 mg/L at the surface to zero at 16 meters (at the
chemocline).
Stratification is persistent and seasonal mixing does not occur. The lake is one of about 200 saline
meromictic lakes that have been identified in the world. However most of these lakes are of
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
origin. Permanently stratified marine lakes are unusual, but on Eil Malk and on other nearby islands there are eleven other permanently stratified marine lakes,
[Stratified marine lakes of Palau (Western Caroline Islands) Physical Geography 19: 175-220, William Hamner, Peggy Hamner] the most renowned one is
Jellyfish Lake.
References
External links
Wondermondo: Clear Lake - marine lake of jellyfishes
{{Koror
Meromictic lakes
Saline lakes of Palau