In the Southern Ocean, occasional abundant growth of tiny plants, phytoplankton, can pull CO2 from the atmosphere. When those plants sink, directly or after serving as food for larger organisms, the Southern Ocean system becomes a net carbon sink, a place where carbon leaves the atmosphere for long-term storage in ocean sediments. Thus, what happens in the Southern Ocean ecosystems affects us all.

In a paper published 14 March 2010, French and Australian researchers have used new IPY measurements of iron in the Southern Ocean (from the IPY Geotraces Project) to test and validate a new model for sources of iron in the Southern Ocean - phytoplankton depend on iron for growth. These researchers have suggested that in addition to iron delivered from above (in atmospheric dust) and from the ocean floor (in resuspended sediments), iron from hydrothermal activity on the ocean floor can increase the Southern Ocean carbon export (sinkage) by 10 to 15%, and by up to 30% in some regions of the Southern Ocean. The figure below shows a model of dissovled iron in the Pacific, with an enrichment (yellow) clearly visible in the Southern Ocean.

The authors say "Marine productivity in the Southern Ocean is limited by the availability of iron and this region is critical in governing atmospheric CO2 levels. Given its importance in controlling ocean [dissolved iron], hydrothermalism should be included in our understanding of the Southern Ocean [dissolved iron] cycle." Read more about this topic in Nature Geoscience.