Climate-Driven Variability in the Southern Ocean Carbonate System

Seasonal and interannual variability in the Southern Ocean carbonate system is investigated using output from a historically forced (1948-2007) ocean general circulation model with embedded biogeochemistry. Atmospheric CO2 is fixed at preindustrial levels to investigate carbonate system variability in the absence of an anthropogenic CO2 perturbation. It is found that nearly a quarter of interannual variability in Southern Ocean Pacific sector surface carbonate ion concentration [GRAPHICS] can be explained by variability in ENSO, with Pacific sector surface [GRAPHICS] decreasing by 0.43 mmol m(-3) per standard deviation decrease in the ENSO-3.4 index. ENSO-related variability in vertical advection of dissolved inorganic carbon (DIC) drives this relationship between ENSO and surface [GRAPHICS] . It is also found that positive phases of the southern annular mode (SAM) are associated with decreased Southern Ocean surface [GRAPHICS] , an association driven by SAM-related variability in vertical advection of DIC. Despite the influence of the SAM on interannual variability in surface [GRAPHICS] , only 4.5% of the trend in natural Southern Ocean surface [GRAPHICS] exhibits linear congruence with the trend in wind stress. Given this, the authors predict that the positive trend in the SAM will not have a substantial impact on ocean acidification. Last, ENSO is found to alter the wintertime minimum in surface [GRAPHICS] . Assuming a business-as-usual acidification rate of 0.5 mmol [GRAPHICS] m(-3) yr(-1), exacerbation of the wintertime minimum during La Nina conditions may advance the date of aragonite undersaturation within the central Pacific sector of the Southern Ocean by as much as 8 yr.