Global significance of nitrous-oxide production and transport from oceanic low-oxygen zones: A modeling study

Recent studies of marine nitrous oxide have focused attention on the suboxic and low-oxygen zones associated with ocean basin eastern boundaries. It has been suggested that complex N₂O cycling mechanisms in these regions may provide a net source to the oceanic interior and a significant portion of the ocean-atmosphere flux. In this study we evaluate the global significance of N₂O formation in these regions. N₂O is treated as a nonconserved tracer in an ocean general circulation model: a simple source function is developed which models N₂O production as a function of organic matter remineralization and local oxygen concentration. Model results are evaluated against both surface and deep observational data sets. The oceanic oxygen minimum zones are predominantly found in the upper water column of tropical latitudes and overlain by regions of strong upwelling in the surface ocean. Simulations of increased N₂O production under low-oxygen conditions indicate that the majority of the N₂O thus formed escapes directly to the atmosphere and is not subject to significant meridional transport. Results indicate that while enhanced N₂O production in these regions cannot be held accountable for the majority of the sea-air flux and interior distribution, it may, however, have significance for the local distribution and provide as much as 25-50% of the global oceanic source.