ABSTRACT
Distribution, formation, and temporal stability of OMZs OMZs generally form where strong upwelling leads to high surface productivity that sinks and degrades, depleting oxygen within the water column. However, OMZ formation also requires stagnant circulation, long residence times (the absence of oxygen exchange), and the presence of oxygen-depleted source waters (Sarmiento et al. 1988). In the absence of exchange by circulation, oxygen is supplied to the OMZ by vertical and horizontal diffusion and by water ascending from below (Wyrtki 1962). Often OMZs support bacterial denitrification in which nitrate ions are used for oxidation of organic matter; in the process they are reduced to molecular nitrogen with nitrite as an intermediate (Codispoti & Christiansen 1989). Nitrification, the oxidation of nitrite and ammonium also occurs in these waters (Ward et al. 1989).
