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Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. [1] Anoxic waters can be contrasted with hypoxic waters, which are low (but not lacking) in dissolved ...
In OMZs oxygen concentration drops to levels <10 nM at the base of the oxycline and can remain anoxic for over 700 m depth. [7] This lack of oxygen can be reinforced or increased due to physical processes changing oxygen supply such as eddy-driven advection, [7] sluggish ventilation, [8] increases in ocean stratification, and increases in ocean temperature which reduces oxygen solubility.
Organisms, both microbial and multicellular, use oxygen in respiration throughout the entire depth of the ocean, so when the supply of oxygen from the surface is less than the utilization of oxygen in deep water, oxygen loss occurs. This phenomenon is natural, but is exacerbated with increased stratification and increasing ocean temperature.
Measurements of primary productivity in the ocean can be made using this ratio. The concentration of oxygen dissolved in seawater varies according to biological processes (photosynthesis and respiration) as well as physical processes (air-sea gas exchange, temperature and pressure changes, lateral mixing and vertical diffusion).
An aquatic system lacking dissolved oxygen (0% saturation) is termed anaerobic, reducing, or anoxic. In water, oxygen levels are approximately 7 ppm or 0.0007% in good quality water, but fluctuate. [5] Many organisms require hypoxic conditions. Oxygen is poisonous to anaerobic bacteria for example. [3]
The word oxygen in the literature typically refers to molecular oxygen (O 2) since it is the common product or reactant of many biogeochemical redox reactions within the cycle. [37] Processes within the oxygen cycle are considered to be biological or geological and are evaluated as either a source (O 2 production) or sink (O 2 consumption). [36 ...
In freshwater or marine systems apparent oxygen utilization (AOU) is the difference between oxygen gas solubility (i.e. the concentration at saturation) and the measured oxygen concentration in water with the same physical and chemical properties.
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.