Ocean anoxia

Ocean anoxia is a condition in which dissolved oxygen is absent or nearly exhausted in part of the ocean. Oxygen is supplied by exchange with the atmosphere, biological production and transport of ventilated water. Respiration and oxidation consume it, so weak renewal combined with a large organic-matter supply can deplete a water body.

Density stratification can restrict exchange between oxygenated surface water and deeper water. Measurements of dissolved oxygen and circulation therefore help distinguish low supply from high consumption. Euxinia additionally requires dissolved sulfide; anoxia alone does not specify which reduced chemical species are present.

Anoxic, sulfide-bearing conditions in a water body. Euxinia combines oxygen absence with dissolved sulfide, potentially adding toxicity to the habitat loss caused by ocean anoxia. It is a chemical state rather than a synonym for every low-oxygen environment.