Southern Annular Mode Influence on Wintertime Ventilation of the Southern Ocean Detected in Atmospheric O2 and CO2 Measurements

Abstract

Abstract The Southern Annular Mode (SAM) is the dominant mode of climate variability in the Southern Ocean, but only a few observational studies have linked variability in SAM to changes in ocean circulation. Atmospheric potential oxygen (APO) combines atmospheric O2/N2 and CO2 data to mask the influence of terrestrial exchanges, yielding a tracer that is sensitive mainly to ocean circulation and biogeochemistry. We show that observed wintertime anomalies of APO are significantly correlated to SAM in 25‐ to 30‐year time series at three Southern Hemisphere sites, while CO2 anomalies are also weakly correlated. We find additional correlations between SAM and O2 air‐sea fluxes in austral winter inferred from both an atmospheric inversion of observed APO and a forced ocean biogeochemistry model simulation. The model results indicate that the correlation with SAM is mechanistically linked to stronger wind speeds and upwelling, which brings oxygen‐depleted deep waters to the surface.

Keywords

• atmospheric potential oxygen
• carbon dioxide
• air‐sea flux
• Antarctic oscillation
• Southern Annular Mode
• seasonal cycles