Evaluating Methane Emissions and Sea-Air Fluxes in the Southern Ocean

The ocean is generally thought to be a small source of atmospheric methane. However, the contribution of the Southern Ocean remains poorly quantified due to its remoteness and lack of measurements. In this study we investigate sea-air methane fluxes in the Southern Ocean measured by two different methods, bulk flux and eddy-covariance, to better understand the region's role in global methane emissions. We focus on both on-shelf and off-shelf areas, including regions where methane seeps from the seabed into the water column, using several years of ship-based measurements.

Our results show that coastal and on-shelf regions of the Southern Ocean, including areas with known seabed seeps, act as small sources of methane to the atmosphere. This is possibly driven by methane produced at the seabed reaching the surface or inputs from terrestrial sources, such as subglacial discharge. We also find possible indications of increased methane release from coastal areas compared to previous studies. Given the potential for increased methane release from these regions in the future under a warming climate, our findings emphasise the importance of ongoing monitoring in the Southern Ocean to quantify its contribution to the global methane cycle and track any changes over time.

Open ocean sea-air methane flux measurements in the Scotia and Weddell Seas during consecutive Antarctic summers revealed a source and a sink of methane depending on the method used (bulk flux or eddy-covariance). As these measurements techniques were not deployed simultaneously, a dedicated measurement campaign is necessary to collect parallel data and better understand whether the observed differences reflect measurement technique variability or potential changes in the Southern Ocean system.