Methane Emissions and Dynamics in the Weddell and Scotia Seas

Abstract

The Southern Ocean's role in the global methane (${\text{CH}}_4$) cycle remains uncertain due to limited measurement data from this remote region. It is unclear if the Southern Ocean acts as a source or sink of atmospheric ${\text{CH}}_4$, and climatic changes can have consequences on the amount of marine ${\text{CH}}_4$ released due to the acceleration of glacial melting and uncertain consequences on seabed ${\text{CH}}_4$ reservoirs. Monitoring ${\text{CH}}_4$ here is essential to understanding its impact on the global ${\text{CH}}_4$ budget now and in the future. This study measured ${\text{CH}}_4$ concentrations in both ocean and atmosphere during an expedition in the Scotia Sea, Weddell Sea, and South Georgia shelf, linking seabed activity, water column concentrations, sea-air fluxes, and atmospheric ${\text{CH}}_4$ levels. All areas were found to be a small source of ${\text{CH}}_4$ to the atmosphere. Surface water ${\text{CH}}_4$ concentrations of off-shelf waters were found to be lower south of the Southern Antarctic Circumpolar Current front, where upwelling brings ${\text{CH}}_4$-depleted waters to the surface. On-shelf regions show higher ${\text{CH}}_4$ emissions compared to off-shelf, with average sea-air ${\text{CH}}_4$ fluxes of 0.269 $\pm$ 0.035 μmol m⁻² d⁻¹ and 0.136 $\pm$ 0.021 μmol m⁻² d⁻¹, respectively, likely due to seabed seepage and methane-enriched freshwater. This study finds that the Weddell and Scotia seas (including the South Georgia shelf) are a small source of atmospheric ${\text{CH}}_4$. As this result contradicts previous studies identifying this area as a ${\text{CH}}_4$ sink, continued monitoring is needed to understand how emissions are changing and may continue to change in the future.