A biologically constrained estimate of oceanic N₂O flux

Abstract

An estimate of the annual production rate of N₂O in the oceans was derived through consideration of biological processes yielding this trace gas. Under an assumption that steady state exists, integrated estimates of primary production occurring at the expense of nitrogen imported into the upper euphotic zone of the open ocean and coastal areas (“new production”) were used to place limits on water column nitrification. Estimates of water column and shelf sediment denitrification were compiled. Nitrification was also assumed to provide the substrate for denitrification. N₂O yields from nitrification and denitrification were based on literature values.

Total oceanic N₂O production was calculated as 11 Tg N y⁻¹, which agrees with previous estimates based on observed concentration gradients and modelled N₂O diffusive fluxes. Coastal and coastal upwelling areas accounted for levels of new production and denitrification equivalent to open ocean areas. All open oceans and coastal areas were estimated to produce around 5 Tg N as N₂O per year, with the balance occurring in nearshore/estuarine areas.