Iron(II) in the world's oxygen deficient zones

Oxygen deficient zones (ODZs) are regions in the marine water column where concentration of oxygen is very low or zero and respiration occurs using nitrate as terminal electron acceptor. Under such conditions, iron (Fe) would be predicted to +3 valence state, its geochemistry largely unaffected by absence oxygen. In contrast, observations show that Fe(II) a major sometimes dominant oxidation state ODZs, even presence substantial amount excess nitrate. plays an important role Fe transport ODZs. They generally enriched throughout reduction occurring. Here, it argued maxima arise result processes common Eastern Tropical North South Pacific well Arabian Sea. Recent work has revealed lateral advection from reducing sediments perhaps source appears physical still poorly understood act over surprisingly narrow density range. Tracers including iodine 228Ra have been extremely useful constraining these processes. The findings reported here implications for continental margin ocean interior, microbes involved nitrogen cycle high requirements.