Contributions of denitrification and mixing on the distribution of nitrous oxide in the North Pacific

We analyzed N2O isotopomer ratios (distribution of isotopes within N2O molecules) in the eastern tropical North Pacific. The N2O isotopomer ratios indicate the contribution of denitrification in the oxygen minimum zone (OMZ, similar to 600 m in depth) in the western North Pacific, which is not consistent with the widely accepted nitrification hypothesis. Our models indicate that the N2O yield per mole O-2 consumed (dN(2)O/-dO(2)) is 0.008 ( 0 - 0.015) nmol/mumol during remineralization and nitrification in the western North Pacific. Nitrification in aerobic deep waters is a minor source of oceanic N2O, whereas the N2O production in the OMZ is the dominant factor for the oceanic N2O distribution. The denitrification in the OMZ is consistent with the correlation between DeltaN(2)O ( level above atmospheric equilibrium) and AOU (apparent oxygen utilization), and the parallel O-18-enrichment of N2O and O-2 in the OMZ, which have been believed to support the nitrification hypothesis.