Conundrum of missing iron in oxygen minimum zones solved

Iron is an essential nutrient for biological productivity in the oceans. However, dissolved iron quickly combines with oxygen and is then no longer usable by organisms. For a long time it has been a conundrum why even in low oxygen zones of the Tropics the dissolved iron concentrations are relatively low. An international research has now discovered that in anoxic seawater, iron is removed through reaction with nitrate instead of oxygen.