Ocean anoxia

Ocean anoxia is a condition in which seawater contains too little dissolved oxygen to sustain most oxygen-dependent marine life. It can affect isolated basins, coastal waters, or large portions of the ocean.

Ocean deoxygenation: The decline of dissolved oxygen in ocean waters over time. Anoxia is the most severe end of this broader decline.
Gulf of Mexico dead zone: A seasonally recurring hypoxic region in the northern Gulf of Mexico, driven largely by nutrient runoff. It demonstrates how land-derived nutrients can trigger severe oxygen loss in coastal waters.
Marine dead zone: A marine area with oxygen levels too low for many organisms to survive or remain active. Anoxic waters can create dead zones where mobile animals flee and less-mobile life dies.
Marine hypoxia: A condition in which dissolved oxygen in marine water is low enough to stress or harm organisms. Hypoxia means oxygen is depleted but not necessarily absent, unlike anoxia.
Stratification: The layering of water masses by density, which limits vertical mixing. Strong layering can isolate deep water from oxygen supplied at the surface.
Black Sea: A large inland sea whose deep waters are permanently anoxic beneath an oxygenated surface layer. Its persistent stratification preserves a modern example of a vast anoxic basin.
Benthic zone: The ecological region at the bottom of a sea or ocean, including its sediment surface. Bottom-dwelling communities encounter anoxia first when oxygen-poor water reaches the seafloor.
Dysoxia: A state of extremely low dissolved oxygen that falls between ordinary oxygenation and anoxia. The term describes near-anoxic conditions where traces of oxygen remain.
Eutrophication: Excess nutrient enrichment that stimulates biological production and can deplete oxygen during decomposition. Nutrient-driven blooms supply sinking organic matter whose decay consumes oxygen.
Cariaco Basin: A deep basin in the Caribbean Sea with oxygen-poor bottom waters and sediment records of past climate. Its sediments preserve evidence of changing anoxia and productivity through time.

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