OMZ, oxygen minimum zones. Whitin the OMZ , created due to high activity and high oxygen consumption, oxygen can not be delivered in time to fulfill the demand, anoxic zones may be created. The condition is called anoxic when the DO drops below +- 0,5ppm. This condition is also created within a nitrifying biofilm at a normal DO level ( Micro OMZ) Also in an aquarium, in places with a low water exchange ratio or when high oxygen demand exceeds the supply.ANAMMOX does not need a substrate and are very common in our oceans
By oceans, you mean areas in the ocean where D/O is below 0.05ppm?