Clear Lake (also Clearwater Lake) is a marine lake located on

Eil Malk Eil Malk or Mecherchar is the main island of the Mecherchar Islands, an island group of Palau in the Pacific Ocean. In a more narrow sense, just the southeastern peninsula of Mecherchar is called Eil Malk. Geography Eil Malk is located 23 kil ...

island in

Palau Palau,, officially the Republic of Palau and historically ''Belau'', ''Palaos'' or ''Pelew'', is an island country and microstate in the western Pacific. The nation has approximately 340 islands and connects the western chain of the Caro ...

. 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 25 ...

, 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 (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life fo ...

, the other lakes being

Jellyfish Lake Jellyfish Lake ( pau, Ongeim'l Tketau, lit=Fifth Lake) is a marine lake located on Eil Malk island in Palau. Eil Malk is part of the Rock Islands, a group of small, rocky, mostly uninhabited islands in Palau's Southern Lagoon, between Koror an ...

, Goby Lake, Uet era Ngermeuangel,

Uet era Ongael Uet era Ongael (Ongael Lake) is a marine lake located on Ongael Island, Koror, in Palau. There are about 70 other marine lakes located throughout the Rock Islands and Koror. Uet era Ongael is notable for endemic subspecies of golden jellyfish an ...

Golden jellyfish

Clear Lake is one of the oldest of

meromictic A meromictic lake is a lake which has layers of water that do not intermix. In ordinary, holomictic lakes, at least once each year, there is a physical mixing of the surface and the deep waters. The term ''meromictic'' was coined by the Austri ...

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 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 means "less recen ...

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 Stratification may refer to: Mathematics * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Data stratification in statistics Earth sciences * Stable and unstable stratification * Stratification, or st ...

into two layers, an oxygenated upper layer (mixolimnion) and a lower

anoxic The term 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 diss ...

layer (monimolimnion). The oxygen concentration in the lake declines from about 6 mg/L at the surface to zero at 16 meters (at the

chemocline A chemocline is a type of cline, a layer of fluid with different properties, characterized by a strong, vertical chemistry gradient within a body of water. In bodies of water where chemoclines occur, the cline separates the upper and lower layers, ...

). Stratification is persistent and seasonal mixing does not occur. The lake is one of about 200 saline

lakes that have been identified in the world. However most of these lakes are of freshwater 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

References

External links

Wondermondo: Clear Lake - marine lake of jellyfishes
{{Koror Lakes of Palau Meromictic lakes Saline lakes of Oceania