Global mapping of flux and microbial sources for oceanic N2O

The ocean is the largest source of N₂O emissions from global aquatic ecosystems. However, the N₂O production-consumption mechanism and microbial spatial distribution are still unclear. Our study established a bottom-up model based on the source‒sink boundary and the microbial sources of N₂O. A high-resolution (0.1°) global distribution of oceanic N₂O was depicted, confirmed by approximately 150,000 surface measurements. The microbial N₂O flux is 2.9 Tg/yr N-N₂O, with the oxygen-deficient zones (ODZs) disproportionately accounting for more than half of the total emission. High primary productivity, sharp oxyclines, and shallow emission depths caused the ODZs to be N₂O hotspots. Geographically, ammonia-oxidizing archaea (AOA, 1.0 Tg) are the most widely distributed contributors to N₂O emissions in the ocean, completely overtaking ammonia-oxidizing bacteria (AOB). Heterotrophic denitrification, mainly occurring in ODZs, contributes the most (1.6 Tg) to N₂O emissions. Overall, this study offers a bottom-up framework for understanding microbial source-sink mechanism in the ocean.