Anoxia means a total depletion in the level of

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 ...

, 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 oxygen *

Anoxic event An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic ( anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geol ...

, when the Earth's oceans become completely depleted of oxygen below the surface levels *

Euxinic Euxinia or euxinic conditions occur when water is both wikt:anoxic, anoxic and wikt:sulfidic, sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen sulfide (H2S). Euxinic bodies of water are frequently strongly strat ...

, anoxic conditions in the presence of hydrogen sulfide *

Hypoxia (environmental) Hypoxia (''hypo'': 'below', ''oxia'': 'oxygenated') refers to low oxygen conditions. Hypoxia is problematic for air-breathing organisms, yet it is essential for many anaerobic organisms. Hypoxia applies to many situations, but usually refers t ...

, low oxygen conditions * Hypoxia (medicine), when the body or a region of the body is deprived of adequate oxygen supply ** Cerebral anoxia, when the brain is completely deprived of oxygen, an extreme form of

cerebral hypoxia Cerebral hypoxia is a form of Hypoxia (medical), hypoxia (reduced supply of oxygen), specifically involving the human brain, brain; when the brain is completely deprived of oxygen, it is called ''cerebral anoxia''. There are four categories of c ...

See also