Multi-decadal trends in the advection and mixing of natural carbon in the Southern Ocean

Multi-decadal trends in the advection, mixing, and air-sea flux of natural carbon dioxide (CO₂) in the Southern Ocean are investigated using output from a hindcast simulation of a non-eddy-resolving ocean model. Particular emphasis is placed on the model's improved eddy-induced advection parameterization. From 1958 to 2007, the model predicts a significant increase in the outgassing of natural CO₂ from the Southern Ocean, congruent with a positive trend in the wind speed over this period. The natural CO₂ flux trend is largely driven by enhanced Eulerian-mean advection and diapycnal mixing of dissolved inorganic carbon (DIC) into the Southern Ocean surface. The natural CO₂ flux trend would be larger, if not for an increase in the eddy-induced advection of DIC out of the Southern Ocean surface, caused by the multi-decadal increase in the model's eddy-induced advection coefficient.