Decoupling of N₂O Production and Emissions in the Northern Indian Ocean

The northern Indian Ocean is a hotspot of nitrous oxide ((Formula presented.) O) emission to the atmosphere. Yet, the direct link between production and emission of (Formula presented.) O in this region is still poorly constrained, in particular the relative contributions of denitrification, nitrification and ocean transport to the (Formula presented.) O efflux. Here, we implemented a mechanistically based (Formula presented.) O cycling module into a regional ocean model of the Indian Ocean to examine how the biological production and transport of (Formula presented.) O control the spatial variation of (Formula presented.) O emissions in the basin. The model captures the upper ocean physical and biogeochemical dynamics of the northern Indian Ocean, including vertical and horizontal (Formula presented.) O distribution observed in situ and regionally integrated (Formula presented.) O emissions of 286 (Formula presented.) 152 Gg N (Formula presented.) (annual mean (Formula presented.) seasonal range) in the lower range of the observation-based reconstruction (391 (Formula presented.) 237 Gg N (Formula presented.)). (Formula presented.) O emissions are primarily fueled by nitrification in or right below the surface mixed layer ((Formula presented.) 57%, including 26% in the mixed layer and 31% right below), followed by denitrification in the oxygen minimum zones ((Formula presented.) 30%) and (Formula presented.) O produced elsewhere and transported into the region ((Formula presented.) 13%). Overall, (Formula presented.) 74% of the emitted (Formula presented.) O is produced in subsurface and transported to the surface in regions of coastal upwelling, winter convection or turbulent mixing. This spatial decoupling between (Formula presented.) O production and emissions underscores the need to consider not only changes in environmental factors critical to (Formula presented.) O production (oxygen, primary productivity etc.) but also shifts in ocean circulation that control emissions when evaluating future changes in global oceanic (Formula presented.) O emissions.