Southern Ocean Storms Drive Massive Surge in Nitrous Oxide Emissions

The bottom line

Extratropical cyclones are forcing a radical reassessment of marine greenhouse gas budgets. Historical data, biased towards calm weather, has severely underestimated the volume of gas released by the Southern Ocean. By integrating storm data, researchers identified an 88% increase in net annual nitrous oxide emissions. The ocean is not the silent sink previously modelled.

The volatility of nitrous oxide emissions

Nitrous oxide (N2O) is the dominant ozone-depleting agent of the 21st century. It is a potent greenhouse gas. Yet, marine estimates remain imprecise. The primary obstacle is spatiotemporal variability. Traditional shipboard measurements fail here. Vessels avoid the violent storms that define the Southern Ocean. Consequently, scientists relied on a static assumption: a standard surface pressure of 1 atmosphere.

This assumption ignores the physical reality of weather. It creates a data blind spot. To bypass the limitations of human-crewed ships, the study utilised machine learning applied to biogeochemical Argo floats. These robotic profilers operate autonomously. They drift and dive, collecting data regardless of surface turbulence. This approach allowed for the derivation of N2O observations during the most intense weather events.

Mechanism: Pressure gradients

Physics drives the flux. Extratropical cyclones create low-pressure systems. As these storms pass, atmospheric pressure drops significantly while wind speeds accelerate. This combination disrupts the air-sea equilibrium. The ocean holds concentrations of N2O. When the pressure drops and the surface churns, the gas escapes.

The study measured how these storms amplify air-sea gradients. They create temporary, intense hotspots of outgassing. It is a forced exhalation. By factoring in these pressure drops rather than assuming a calm 1 atmosphere, the calculated flux nearly doubles. The storm facilitates the release of gas that would otherwise remain dissolved.

Impact: A weaker sink

The revision is arithmetic and absolute. An 88% increase in flux alters the global equation. Current climate models often treat the Southern Ocean as a robust sink for greenhouse gases. This study suggests that capacity is overstated. If the ocean releases significantly more N2O during storms than previously understood, its net benefit to the global greenhouse gas budget decreases.

The implications extend to ozone recovery and radiative forcing. N2O persists in the atmosphere. These findings, derived from machine-learning models applied to float data, highlight a critical gap in previous observations. We are likely undercounting the total volume of gas emerging from polar waters. The Southern Ocean plays a significant role in the global N2O cycle, but it is a more volatile participant than static models admit.