The Southern Ocean plays an important role in the exchange of carbon dioxide between the atmosphere and the ocean. One aspect of this is the growth of phytoplankton, which acts as a natural sponge for carbon dioxide, drawing the troublesome greenhouse gas from the atmosphere into the sea. When these plankton die they can sink to the bottom of the ocean and store some of the carbon dioxide they have absorbed, a process scientists call the "biological carbon pump."
Although many areas of the Southern Ocean are rich in nutrients, they often lack iron, which limits phytoplankton growth. An important idea in oceanography is that adding iron to the Southern Ocean could stimulate phytoplankton growth and the biological carbon pump. Some scientists believe that this process can partly explain cycles in atmospheric carbon dioxide over Earth's recent history and it has also been widely debated as a mitigation strategy for climate change.