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The exaerobic zone is found at the boundary of anoxic and hypoxic zones. Hypoxia can occur throughout the water column and also at high altitudes as well as near sediments on the bottom. It usually extends throughout 20–50% of the water column, but depends on the water depth and location of pycnoclines (rapid changes in water density with depth).
The climate and ecology of different locations on the globe naturally separate into life zones, depending on elevation, latitude, and location.The generally strong dependency on elevation is known as altitudinal zonation: the average temperature of a location decreases as the elevation increases.
Permanent dead zones are deep water occurrences that rarely exceed 2 milligrams per liter. Temporary dead zones are short lived dead zones lasting hours or days. Seasonal dead zones are annually occurring, typically in warm months of summer and autumn. Diel cycling hypoxia is a specific seasonal dead zone that only becomes hypoxic during the night
The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas. It was first published by Leslie Holdridge in 1947, and updated in 1967. It is a relatively simple system based on few empirical data, giving objective criteria. [ 1 ]
The change has been fairly rapid and poses a threat to fish and other types of marine life, as well as to people who depend on marine life for nutrition or livelihood. [7] [46] [8] [9] As low oxygen zones expand vertically nearer to the surface, they can affect coastal upwelling systems such as the California Current on the coast of Oregon (US).
The life zone concept was developed by C. Hart Merriam in 1889 as a means of describing areas with similar plant and animal communities. Merriam observed that the changes in these communities with an increase in latitude at a constant elevation are similar to the changes seen with an increase in elevation at a constant latitude. [1]
Dead phytoplankton and other organisms sink to the bottom giving rise to large numbers of decomposers due to increased food supply (dead organisms, phytoplankton). Due to the increased number of decomposers that use more oxygen, fish and shrimp at the lower layers of the ocean become oxygen-starved, resulting in the creation of hypoxic zones.
In mountaineering, the death zone refers to altitudes above which the pressure of oxygen is insufficient to sustain human life for an extended time span. This point is generally agreed as 8,000 m (26,000 ft), where atmospheric pressure is less than 356 millibars (10.5 inHg; 5.16 psi). [ 1 ]