The remote Southern Ocean plays an important, yet poorly understood, role in the global carbon cycle.Deep water surfaces in the southern part of the Antarctic Circumpolar Current (ACC) and near the Antarctic continent.This water exchanges heat, carbon dioxide (CO2) and other gases with the atmosphere, before leaving the surface again elsewhere in the Southern Ocean.These processes make the Southern Ocean an important area for ventilation of CO2 from the deep ocean towards the atmosphere.Biological activity is relatively low in many parts of the Southern Ocean, despite high concentrations of macro-nutrients in the upwelled water.Iron enrichment experiments have demonstrated that low iron availability limits algal growth in some areas.Wind-driven deep mixing, resulting in light limitation, and grazing by zooplankton are other causes for low phytoplankton productivity.A reduction in the deposition of dust-derived iron at the end of ice ages may have reduced algal growth in the Southern Ocean, which may have promoted an increase in the atmospheric level of the greenhouse gas CO2.This may have been an important mechanism in glacial to interglacial climate change.Human activities are releasing vast amounts of CO2 into the atmosphere.Model results and scarce oceanographic observations suggest a net oceanic CO2 sink of 0.1-0.5 Pg C yr-1 (Pg = 1015 g) south of 50ºS, 6-29% of the net global oceanic sink of anthropogenic CO2.This implies that uptake ofextra CO2 has changed the Southern Ocean's natural CO2 source into a net sink.Ongoing research intends to test this hypothesis for the Southern Ocean's Atlantic sector by extending the longest time series (since 1984) of total dissolved inorganic carbon and transient tracer data along 0ºW.In addition, available surface water CO2 data will be compiled for the Atlantic sector and the remote Weddell Sea.Recent results will be discussed.