Nitrous oxide from anammox

During the last years, anaerobic ammonium oxidation (anammox, NO2~ + NH4+ ^ N2) has received increasing attention as an additional, previously not recognized, significant loss process of fixed nitrogen in the ocean (see for example Francis et al, 2007; Devol, 2008). N2O has been found to be formed only in small amounts during nitric oxide detoxification (NO2~ ^ NO ^ N2O) that seems to be performed by the anammox bacterium Kuenenia stuttgartiensis as a side reaction of the anammox reaction (Kartal et al, 2007). Anammox has been found in the sub-oxic zones of eastern tropical South Pacific Ocean, in the upwelling off Namibia (Kuypers et al, 2005; Thamdrup et al, 2006; Hamersley et al, 2007) as well as in the central Baltic Sea (Hannig et al, 2007), but not in the sub-oxic zones of the central Arabian Sea (Nicholls et al, 2007). The question of whether anammox is involved in the production and/or consumption of N2O in the ocean should be the subject of further investigation.

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