The Southern Ocean is net source of the potent greenhouse gas nitrous oxide to the atmosphere. Marine nitrous oxide emissions are difficult to constrain, however, due to their sharp gradients and small scales of variability in both space and time. In the Southern Ocean, where extratropical cyclones create conditions conducive to high air-sea gas flux, traditional shipboard sampling is unlikely to capture the full extent of nitrous oxide emissions due to the inability to sample in the centers of such storms. Here, we propose that the Southern Ocean nitrous oxide source is almost double the magnitude of previous estimates, based on machine learning-derived nitrous oxide observations from biogeochemical Argo floats. Our results suggest that the low-pressure centers inside extratropical cyclones amplify air-sea nitrous oxide disequilibria and create brief, intense pulses of nitrous oxide to the atmosphere. We demonstrate further that taking these low-pressure centers into account, instead of assuming a barometric pressure of 1 atmosphere, increases the overall magnitude of the Southern Ocean nitrous oxide source by 150%, explaining the discrepancy between previous work and our higher, more comprehensive estimate. Our results imply that the Southern Ocean plays a significant role in the global nitrous oxide cycle and may be a weaker net sink of greenhouse gases than previously thought.

BGC Argo,machine learning,nitrous oxide,greenhouse gases,biogeochemistry