Factors governing the oceanic nitrous oxide distribution: Simulations withan ocean general circulation model

A global model of the oceanic nitrous oxide distribution is developed to ev aluate current understanding of the processes governing nitrous oxide forma tion and distribution in the open ocean. N2O is treated as a nonconserved t racer in a global ocean general circulation model subject to biological sou rces in the oceanic interior and gas exchange at the ocean surface. A simpl e scalar parameterization linking N2O production to oxygen consumption land based on observed correlations between excess N2O and apparent oxygen util ization) is successful in reproducing the large-scale features of the obser ved distribution, namely, high surface supersaturations in regions of upwel ling and biological productivity, and values close to equilibrium in the ol igotrophic subtropical gyres. The majority of the oceanic N2O source is pro duced in the upper water column lover 75% above 600 m) and effluxes directl y to the atmosphere in the latitude band of formation. The observed structu re at depth is not as well reproduced by this model, which displays excessi ve N2O production in the deep ocean. An alternative source parameterization , which accounts for processes which result in a depth variation in the rel ationship between N2O production and oxygen consumption, yields an improved representation of the deep distribution. The surface distribution and sea- air flux are, however, determined primarily by the upper ocean source and, therefore, are relatively insensitive to changes in the nature of deep ocea nic N2O production.