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Contributions of denitrification and mixing on the distribution of nitrous oxide in the North Pacific
Department of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama, Japan
Solution Oriented Research for Science and Technology (SORST) Project, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, Japan
Department of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama, Japan
Solution Oriented Research for Science and Technology (SORST) Project, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, Japan
Frontier Collaborative Research Center, Tokyo Institute of Technology, Yokohama, Japan
Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Yokohama, Japan
Solution Oriented Research for Science and Technology (SORST) Project, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, Japan
Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Yokohama, Japan
Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii, USA
Department of Oceanography, University of Hawaii, Honolulu, Hawaii, USA
Department of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama, Japan
Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology, Mutsu, Aomori, Japan
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, ∼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 O2 consumed (dN2O/−dO2) is 0.008 (0–0.015) nmol/μmol 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 ΔN2O (level above atmospheric equilibrium) and AOU (apparent oxygen utilization), and the parallel 18O-enrichment of N2O and O2 in the OMZ, which have been believed to support the nitrification hypothesis.
Received 10 September 2004; accepted 12 January 2005; published 18 February 2005.
Citation: (2005), Contributions of denitrification and mixing on the distribution of nitrous oxide in the North Pacific, Geophys. Res. Lett., 32, L04603, doi:10.1029/2004GL021458.
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