Meeting Documents

Recent Changes in Global Ocean N₂O Fluxes and Their Relationship to Ocean Climate Variability: A Modeling Study

Abstract

The ocean plays an important role in regulating atmospheric N₂O levels, however, its contribution remains poorly constrained. Here, we implemented an N₂O module into the Estimating Circulation and Climate of the Ocean-Darwin (ECCO-Darwin) ocean biogeochemistry state to estimate global sea-air N₂O fluxes, trends and interannual variabilities. From 1992 to 2017, the model computed that the ocean released about 2.43 Tg N yr^-1, showing a declining trend of -0.0194 Tg N yr^-1. The Eastern Tropical Pacific (ETP), Indian Ocean (IO) and Southern Ocean (SO) are the three hotspots for N₂O outgassing, where interannual variability is strongly affected by regional climate modes. In the ETP and IO, oceanic N₂O fluxes are strongly correlated with the ENSO index, with correlation coefficients of r = -0.93 and 0.53, respectively. During the positive phase of ENSO (El Niño), reduced wind speeds and the deepening of the thermocline lead to decreased N₂O outgassing in the ETP. El Niño events also tend to result in a positive Indian Ocean Dipole (IOD), which causes the thermocline in the Eastern Tropical IO to shoal, resulting in increased N₂O outgassing. In the SO, the interannual variability of N₂O fluxes is postively correlated with the Southern Annular Mode (SAM) index (r = 0.76). When the SAM is positive, westerly winds shift poleward, strengthening Ekman pumping and resulting in more subsurface N₂O-rich water being upwelled and outgassed. Our study for the first time provides mechanistic understanding of the critical role of ocean-atmosphere dynamics and climate variability in modulating oceanic N₂O emissions.View Document (AGU) »