Description: Upon one decade of research it is a well established fact that iron limits photosynthetic CO2 fixation and phytoplankton growth in the Southern Ocean - intense blooms are scarse. However, the input of iron to the Southern Ocean is considerable. An important factor for diminished phytoplankton production refers to the meridional circulation of the Southern Ocean. Intense upwelling of Upper Circumpolar Deep Water (UCDW) causes a large iron flux into the surface layer. However, the main entrainment of upwelled UCDW into the surface layer occurs in autumn and winter which strongly restricts the usefullness of iron supply for phytoplankton due to unfavorable light conditions. Moreover, the meridional transport within the Ekman layer is intense enough to export at least 25% of the iron input away form the Antarctic Zone before it can be used by phytoplankton. This also depresses the potential phytoplankton primary production by at least 25%. Most iron that crosses the Polar Front unused leaves the surface ocean north of the Polar Front because the surface water participates in Antarctic Intermediate Water/Mode Water formation.

Description: As part of the global synthesis effort sponsored by the Global Carbon Cycle project of the National Oceanic and Atmospheric Administration (NOAA) and U.S. Department of Energy, a comprehensive comparison was performed of inorganic carbon parameters measured on oceanographic surveys carried out under auspices of the Joint Global Ocean Flux Study and related programs. Many of the cruises were performed as part of the World Hydrographic Program of the World Ocean Circulation Experiment and the NOAA Ocean-Atmosphere Carbon Exchange Study. Total dissolved inorganic carbon (DIC), total alkalinity (TAlk), fugacity of CO2, and pH data from twenty-three cruises were checked to determine whether there were systematic offsets of these parameters between cruises. The focus was on the DIC and TAlk state variables. Data quality and offsets of DIC and TAlk were determined by using several different techniques. One approach was based on crossover analyses, where the deep-water concentrations of DIC and TAlk were compared for stations on different cruises that were within 100 km of each other. Regional comparisons were also made by using a multiple-parameter linear regression technique in which DIC or TAlk was regressed against hydrographic and nutrient parameters. When offsets of greater than 4 μmol/kg were observed for DIC and/or 6 μmol/kg were observed for TAlk, the data taken on the cruise were closely scrutinized to determine whether the offsets were systematic. Based on these analyses, the DIC data and TAlk data of three cruises were deemed of insufficient quality to be included in the comprehensive basinwide data set. For several of the cruises, small adjustments in TAlk were recommended for consistency with other cruises in the region. After these adjustments were incorporated, the inorganic carbon data from all cruises along with hydrographic, chlorofluorocarbon, and nutrient data were combined as a research-quality product for the scientific community.

Description: 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.