Satellite ocean color data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) were used to examine distributions of chlorophyll concentration within the Southern Ocean for the period October 1997 through September 1998. Over most of the Southern Ocean, mean chlorophyll concentrations remained quite low (< 0.3–0.4 mg m⁻³). Phytoplankton blooms where chlorophyll concentration exceeded 1.0 mg m⁻³ were observed in three general areas, which included coastal/shelf waters, areas associated with the seasonal sea ice retreat, and the vicinity of the major Southern Ocean fronts. These chlorophyll distribution patterns are consistent with an iron-limited system. Mean chlorophyll concentrations from SeaWiFS are compared with values from the coastal zone color scanner (CZCS). The SeaWiFS global chlorophyll algorithm works better than the CZCS in Southern Ocean waters. Primary production in the Southern Ocean was estimated with the vertically generalized production model of Behrenfeld and Falkowski [1997]. Annual primary production in the Southern Ocean (>30°S) was estimated to be 14.2 Gt C yr⁻¹, with most production (∼80%) taking place at midlatitudes from 30° to 50°S. Primary production at latitudes >50°S was estimated to be 2.9 Gt C yr⁻¹. This is considerably higher than previous estimates based on in situ data but less than some recent estimates based on CZCS data. Our estimated primary production is sufficient to account for the observed Southern Hemisphere seasonal cycle in atmospheric O₂ concentrations.

The location of the Antarctic Polar Front (PF) was mapped over a 7-year period (1987–1993) within images of satellite-derived sea surface temperature. The mean path of the PF is strongly steered by the topographic features of the Southern Ocean. The topography places vorticity constraints on the dynamics of the PF that strongly affect spatial and temporal variability. Over the deep ocean basins the surface expression of the PF is weakened, and the PF meanders over a wide latitudinal range. Near large topographic features, width and temperature change across the front increase, and large-scale meandering is inhibited. Elevated mesoscale variability is seen within and downstream of these areas and may be the result of baroclinic instabilities initiated where the PF encounters large topographic features. The strong correlations between topography and PF dynamics can be understood in the context of the planetary potential vorticity (PPV orf/H) field. Mean PPV at the PF varies by more than a factor of 2 along its circumpolar path. However, at the mesoscale the PF remains within a relatively narrow range of PPV values around the local mean. Away from large topographic features, the PF returns to a preferred PPV value of ∼25 × 10⁻⁹ m⁻¹ s⁻¹ despite large latitudinal shifts. The mean paths of the surface and subsurface expressions of the PF are closely coupled over much of the Southern Ocean.

The path of the Antarctic Polar Front (PF) is mapped using satellite sea surface temperature data from the NOAA/NASA Pathfinder program. The mean path and variability of the PF are strongly influenced by bathymetry. Meandering intensity is weaker where the bathymetry is steeply sloped and increases in areas where the bottom is relatively flat. There is an inverse relationship between meandering intensity and both the width of the front and the change in temperature across it There is a persistent, large separation between the surface and subsurface expressions of the PF at Ewing Bank on the Falkland Plateau.

Analysis of satellite ocean color, sea surface temperature, and sea ice cover data reveals consistent patterns between biological production, iron availability, and physical forcings in the Southern Ocean. The consistency of these patterns, in conjunction with information on physical conditions during the last glacial maximum (LGM), enables estimates of export production at the LGM. The LGM Southern Ocean experienced increased wind speeds, colder sea surface and atmospheric temperatures, increased deposition of atmospheric dust, and a greatly expanded winter sea ice cover. These variations had strong effects on Southern Ocean ecology and on air-sea fluxes of CO₂. The seasonal ice zone (SIZ) was much larger at the LGM (30 million km²) than at present (19 million km²). The Antarctic Polar Front (PF) likely marked the northern boundary of this expanded SIZ throughout the Southern Ocean, as it does today in the Drake Passage region. A large northward shift in the position of the PF during glacial times is unlikely due to topographic constraints. North of the PF, the increased flux of aeolian dust during glacial times altered phytoplankton species composition and increased export production, and as a result this region was a stronger sink for atmospheric CO₂ than in the modern ocean. South of the PF, interactions between the biota and sea ice strongly influence air-sea gas exchange over seasonal timescales. The combined influence of melting sea ice and increased aeolian dust flux (with its associated iron) increased both primary and export production by phytoplankton over daily-monthly timescales during austral spring/summer, resulting in a strong flux of CO₂ into the ocean. Heavy ice cover would have minimized air-sea gas exchange over much of the rest of the year. Thus, an increased net flux of CO₂ into the ocean is likely during glacial times, even in areas where annual primary production declined. We estimate that export production in the Southern Ocean as a whole was increased by 2.9-3.6 Gt C yr⁻¹ at the LGM, relative to the modern era. Altered seasonal sea ice dynamics would further increase the net flux of CO₂ into the ocean. Thus the Southern Ocean was a strong sink for atmospheric CO₂ and contributed substantially to the lowering of atmospheric CO₂ levels during the last ice age.

SeaWiFS estimates of surface chlorophyll concentrations are reported for the region of the U.S. JGOFS study in the Southern Ocean (∼ 170°W, 60°S). Elevated chlorophyll was observed at the Southern Ocean fronts, near the edge of the seasonal ice sheet, and above the Pacific-Antarctic Ridge. The elevated chlorophyll levels associated with the Pacific-Antarctic Ridge are surprising since even the crest of the ridge is at depths > 2000 m. This elevated phytoplankton biomass is likely the result of mesoscale physical-biological interactions where the Antarctic Circumpolar Current (ACC) encounters the ridge. Four cruises surveyed this region between October 1997 and March 1998, as part of the U.S. JGOFS. Satellite-derived chlorophyll concentrations were compared with in situ extracted chlorophyll measurements from these cruises. There was good agreement (r² of 0.72, from a linear regression of shipboard vs. satellite chlorophyll), although SeaWiFS underestimated chlorophyll concentrations relative to the ship data.