Assessing the importance of the Southern Ocean for natural atmospheric pCO2 variations with a global biogeochemical general circulation model

A global biogeochemical ocean general circulation model (the HAMOCC model) is employed to study the efficiency of the Southern Ocean for enhancing or damping atmospheric pCO2 variations due to (1) internal and (2) external perturbations of the carbon cycle. Internal perturbations are changes of ocean parameters that govern the carbon cycle such as the velocity field, seawater temperature, the uptake rate of carbon and nutrients, and the rain ratio of C(POC):C(CaCO3) in biogenic particle export from the euphotic zone. The model results suggest that the Southern Ocean is more efficient for compensating external pCO2 variations than the North Atlantic. Concerning most biogeochemical parameters associated with the “biological carbon pump” (POC pump and CaCO3 counter pump), the Southern Ocean enhances natural pCO2 variations and dampens those for changes in sea-surface temperature or circulation. Therefore, modifications in the Southern Ocean biogenic carbon pumps may play a key role for natural variations of the atmospheric CO2 content.