An assessment of the role of the marginal ice zone in the carbon cycle of the Southern Ocean

The dense phytoplankton blooms observed in earlier studies in the Southern Ocean Marginal Ice Zone (MIZ) may not be representative of all regions, so that some previous assessments of the overall importance of this system in total primary production may have been overestimated. Recent observations have shown that increased phytoplankton production may not always be associated with the retreating ice-edge, due to the unpredictability of meltwater-induced stability. Complex interactions between the MIZ and hydrographic fronts have also been indicated. A range of simple simulations, based on biomass inventories for the major biogeochemical systems in the Southern Ocean, show that the greater part of chlorophyll biomass is located in the extensive regions between the major fronts. Consideration of the fronts and the MIZ only, which we surmize may be the principal sites of export production, indicates that the MIZ is clearly the most important single feature. Even if the occurrence of MIZ blooms in the simulations is reduced dramatically, such blooms still appear to make a substantial contribution to production and, by implication, carbon export.