Response of sea surface fugacity of CO₂ to the SAM shift south of Tasmania: Regional differences

Abstract

Using observational data collected south of Tasmania during 14 austral summer cruises during 1993–2011, we examined the response of sea surface fugacity of carbon dioxide (fCO2) to the Southern Annular Mode (SAM) shift, which occurred around 2000. In the southern part of the Southern Ocean (SO) or the Polar Zone (PZ) and the Polar Frontal Zone (PFZ), fCO2 increased faster at the sea surface than in the atmosphere before the SAM shift, but not after the shift. In the northern part of the SO or the Subantarctic Zone (SAZ), however, surface fCO2 increased faster than atmospheric fCO2 both before and after the shift. The SAM shift had an important influence on the surface fCO2 trend in the PZ and PFZ but not in the SAZ, which we attribute to differences in regional oceanographic processes (upwelling versus nonupwelling). The SAM shift may have reversed the negative trend of SO CO2 uptake.

Interannual drivers of the seasonal cycle of CO<sub>2</sub> in the Southern Ocean

“…This concurs with previous studies, which suggested that the increase in the SAM during the 1990s resulted in the weakening of the Southern Ocean sink (Le Quéré et al, 2007;Lenton and Matear, 2007;Lovenduski et al, 2007;Lenton et al, 2009;Xue et al, 2015). The work by Fogt et al (2012) bridges the gap between the proposed asymmetric atmospheric circulation of Landschützer et al (2015) and the observed correlation with the SAM of Landschützer et al (2016).…”

“…Conversely, in the eastern Pacific sector of the Southern Ocean, strong cooling overwhelmed increased upwelling . This is supported by observations from the Drake Passage and south of Australia showing that variability of upwelling has affected pCO 2 (Munro et al, 2015;Xue et al, 2015).…”

The reinvigoration of the Southern Ocean carbon sink

“…Nevertheless, these studies tended to support a weakening sink trend up to the mid 2000s. One of these studies (9) also pointed out that the trend may have reversed in recent years, a finding corroborated by the analysis of pCO 2 observations along a single meridional transect south of Tasmania (11).…”

Utilizing the Drake Passage Time-series to understand variability and change in subpolar Southern Ocean pCO<sub>2</sub>

“…followed by a substantial strengthening of the Southern Ocean CO 2 sink since 2002 [Fay and McKinley, 2013;Landschützer et al 2015a;Munro et al 2015a;Xue et al 2015]. Continued observational sampling efforts and coordination are required for quantifying and understanding decadal changes in this important CO 2 sink region.…”