Global mapping of flux and microbial sources for oceanic N2O

Abstract

Abstract 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.