Understanding the oceanic cycling and transport of the climatically relevant greenhouse gas, nitrous oxide (N2O), is imperative for interpreting how it could change with environmental conditions. We studied N2O distributions under biogeochemically and physically diverse environments along the GEOTRACES GP16 section – from the south Pacific oxygen deficient zone (ODZ) to the western oligotrophic gyre – in concert with isotopic measurements of N2O, nitrate, and nitrite, to investigate the interplay of N2O production, consumption, and water mass mixing. We developed an isotope mixing model to determine the relative contributions and distributions of four N2O endmembers. From the model, we found that partial consumption was an essential determinant of the isotopic composition of N2O within the ODZ, but the consumption signal was rapidly diluted outside the ODZ. Keeling model results also demonstrated how N2O can be traced from the ODZ into the Gyre thermocline in the absence of strong production or consumption terms. Outside of the ODZ thermocline, preformed N2O and N2O derived from ammonia oxidizing archaea were largely responsible for its distribution. Lastly, as shown in other modelling work, a moderate positive site preference (~22‰) for N2O production from incomplete denitrification was necessary to produce realistic endmember distributions. Further, our newly developed tracer, D(SP,18), which removes the isotopic impacts of N2O consumption to highlight the role of production, illustrated a bifurcation of δ15Nβ within ODZ waters, highlighting the potential for nitrate and nitrite to contribute differentially to N2O production in on-shelf and off-shelf ODZ waters.
