Southern Annular Mode Influence on Wintertime Ventilation of the Southern Ocean Detected in Atmospheric O<sub>2</sub> and CO<sub>2</sub> Measurements
C. D. Nevison, David R. Munro, Nicole S. Lovenduski, Ralph F. Keeling, Manfredi Manizza, Eric J. Morgan, Christian Rödenbeck
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 O 2 /N 2 and CO 2 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 CO 2 anomalies are also weakly correlated. We find additional correlations between SAM and O 2 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.