Suboxic

Definition

Suboxic is a term used for describing the oxygen concentration in the water column or any other environment where oxygen is strongly limited and shows no perceptible vertical gradients. There are no clear and agreed-upon boundaries between oxic, oxygen deficient, hypoxic, suboxic, and anoxic; however, the boundary between hypoxic and suboxic conditions is widely taken as 10 μM of O₂, a value commonly observed in water bodies with enhanced nitrification due to an upward flux of ammonia. This level probably corresponds to the biochemical threshold below which the dominant electron acceptors are oxidized species of N (nitrate, nitrite) or of metals [Mn(IV), Fe(III)], whereas dissolved oxygen becomes an auxiliary oxidant. In the strongly stratified Black Sea, the suboxic zone is usually at 50–100 m depth and shows <3 μM in O₂ and H₂S. Suboxic zones favor denitrification which in turn removes many essential nutrients from the water column. In astrobiology, suboxic environments...