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The oxygen minimum zone (OMZ), sometimes referred to as the shadow zone, is the zone in which oxygen saturation in seawater in the ocean is at its lowest. This zone occurs at depths of about 200 to 1,500 m (700–4,900 ft), depending on local circumstances.
Global map of low and declining oxygen levels in the open ocean and coastal waters, 2009. [1] The map indicates coastal sites where anthropogenic nutrients have exacerbated or caused oxygen declines to <2 mg/L (<63 μmol/L) (red dots), as well as ocean oxygen minimum zones at 300 m (blue shaded regions).
While oxygen minimum zones (OMZs) occur naturally, they can be exacerbated by human impacts like climate change and land-based pollution from agriculture and sewage. The prediction of current climate models and climate change scenarios is that substantial warming and loss of oxygen throughout the majority of the upper ocean will occur. [ 32 ]
Global map of low and declining oxygen levels in coastal waters (mainly due to eutrophication) and in the open ocean (due to climate change).The map indicates coastal sites where oxygen levels have declined to less than 2 mg/L (red dots), as well as expanding ocean oxygen minimum zones at 300 metres (blue shaded regions).
Maximum numbers of bacteria generally occur at the pycnocline, where phytodetritus accumulates by sinking from the overlying euphotic zone. There, decomposition by bacteria contributes to the formation of oxygen minimum layers in stable waters.
The UN Environment Programme reported 146 dead zones in 2004 in the world's oceans where marine life could not be supported due to depleted oxygen levels. Some of these were as small as a square kilometer (0.4 mi 2 ), but the largest dead zone covered 70,000 square kilometers (27,000 mi 2 ).
Date/Time Thumbnail Dimensions User Comment; current: 15:25, 20 October 2020: 1,239 × 1,752 (196 KB): Balkanique: Uploaded a work by The OCEAN ATLAS 2017 is jointly published by the Heinrich Böll Foundation Schleswig-Holstein, the Heinrich Böll Foundation (national foundation), and the University of Kiel’s Future Ocean Cluster of Excellence.
Euxinia or euxinic conditions occur when water is both anoxic and sulfidic.This means that there is no oxygen (O 2) and a raised level of free hydrogen sulfide (H 2 S). Euxinic bodies of water are frequently strongly stratified; have an oxic, highly productive, thin surface layer; and have anoxic, sulfidic bottom water.