Department of Earth System Science

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.