摘要：

[1] Nitrous oxide (N₂O) is an important atmospheric greenhouse gas and is involved in stratospheric ozone depletion. Analysis of the isotopomer ratios of N₂O (i.e., the intramolecular distribution of ¹⁵N within the linear NNO molecule and the conventional N and O isotope ratios) can elucidate the mechanisms of N₂O production and destruction. We analyzed the isotopomer ratios of dissolved N₂O at a site in the eastern tropical North Pacific (ETNP) and a site in the Gulf of California (GOC). At these sites, the flux of N₂O to the atmosphere is extremely high but denitrification activity in the oxygen minimum zone (OMZ) also reduces N₂O to N₂. We estimated the isotopomeric enrichment factors for N₂O reduction by denitrification. The factor was −11.6 ± 1.0‰ for the bulk (average) N, −19.8 ± 2.3‰ for the center N (-site nitrogen), −3.4 ± 0.3‰ for the end N (β-site nitrogen), and −30.5 ± 3.2‰ for the ¹⁸O of N₂O. Isotopomer analysis of N₂O suggests that nitrifiers should contribute to N₂O production more than denitrifiers at the oxycline above the OMZs in the ETNP (50–80 m) and in the GOC (80–300 m). In contrast, denitrifiers should largely contribute to the N₂O production and consumption in the OMZs both in the ETNP (120–130 m) and in the GOC (600–800 m). The N₂O isotopomer analysis will be a useful tool for resolving the distribution of water masses that carry a signal of N loss by denitrification.

展开