Simulation models predict that the oxygen content of the global ocean will decrease by 25% until the end of the century due to an increased stratification of the oceanic surface waters and a rise in temperature. This loss in oxygen will inevitably lead to an expansion of hypoxic (= reduced oxygen content) and anoxic areas (= areas depleted in oxygen) in the global ocean with major consequences for the oceanic carbon and nitrogen cycling. The potential impact of an expansion of oxygen minimum zones (OMZ) is probably best illustrated by their current role in the global ocean nitrogen (N) cycle. At present, about 30-50% of the nitrogen loss from the global ocean takes place in the 0.1% of ocean volume comprised of OMZ. Hence, OMZ disproportionally influence the nitrogen cycle and connected to that via autotrophy also the carbon cycle.