Climate driven variability in the Southern Ocean carbonate system

We investigate seasonal and interannual variability in the Southern Ocean carbonate system using output from a historically forced (1948-2007) ocean general circulation model with embedded biogeochemistry. Atmospheric CO2 is fixed at pre-industrial levels to investigate carbonate system variability in the absence of an anthropogenic CO2 perturbation. We find that nearly one quarter of interannual variability in Southern Ocean Pacific sector surface carbonate ion concentration (CO23-) can be explained by variability in ENSO, with Pacific sector surface CO23- 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 CO23-. We also find that positive phases of the Southern Annular Mode (SAM) are associated with decreased Southern Ocean surface CO23-, an association driven by SAM-related variability in vertical advection of DIC. Despite the influence of SAM on interannual variability in surface CO23-, we find that only 4.5% of the trend in natural Southern Ocean surface CO23- exhibits linear congruence with the trend in wind stress. Given this, we predict that the positive trend in SAM will not have a substantial impact on ocean acidification. Lastly, we find that ENSO alters the wintertime minimum in surface CO23-. Assuming a business-as-usual acidification rate of 0.5 mmol m−3 yr−1, exacerbation of the wintertime minimum during La Niña conditions may advance the date of aragonite undersaturation within the central Pacific sector of the Southern Ocean by as many as 8 years.

Conrad C. J. & Lovenduski N. S., in press. Climate driven variability in the Southern Ocean carbonate system. Journal of Climate. Article (subscription required).


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