Processes in the Southern Ocean carbon cycle: Dissolution of carbonate sediments and inter-annual variability of carbon fluxes

The Southern Ocean (SO) carbon cycle is and will be undergoing various changes in a high-CO2 world. This thesis analyzes two key processes: dissolution of carbonate sediments on Antarctic shelves and inter-annual variability of upper ocean carbon fluxes. In the first part of the thesis, the main question is whether dissolution of carbonate sediments from Antarctic shelves can be a negative feedback to ocean acidification. Patterns in the CaCO3 distribution are related to primary production in the overlying water column. Based on this relationship, the inventory of CaCO3 on all Antarctic shelves is calculated to be 4 Pg CaCO3. This suggests that dissolution of CaCO3 from the sediments will not delay acidification. The second process study addresses the inter-annual variability of carbon fluxes in the SO related to the Southern Annular Mode (SAM). The positive phase of the SAM is characterized by stronger upwelling of carbon and nutrient-rich deep water. The carbon content of the surface layer increases and more natural carbon is released to the atmosphere. South of the Polar Front, however, more CO2 is drawn down by stronger biological export production.