Abstract

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.

Highlights

  • Phytoplankton bloom dynamics in the Southern Ocean have long represented a paradox for oceanographers

  • Several previous studies argued that the global processing algorithm (GP) used for the coastal zone color scanner (CZCS) consistently underestimated surface chlorophyll concentrations in the Southern Ocean [Mitchell and Holm-Hansen, 1991; Sullivan et al, 1993; Arrigo et al, 1994]

  • ACZCS pigment values were computed with the original global chlorophyll algorithm (GP) [Gordon et al, 1983], and the data were corrected to reflect the Southern Ocean Pigment (SOP) algorithm [Mitchell and Holm-Hansen, 1991] using the correction factors of Arrigo et al [1994] before averaging

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Summary

Introduction

Phytoplankton bloom dynamics in the Southern Ocean have long represented a paradox for oceanographers. The Southern Ocean is the largest highnutrient low-chlorophyll (HNLC) region in the world ocean [Martin, 1990; Minas and Minas, 1992]. Substantial evidence has accumulated that the availability of the micronutrient iron plays a critical role in limiting phytoplankton biomass and production within HNLC regions [Martin et al, 1990a, 1990b; de Baar et al, 1995; Coale et al, 1996; Gordon et al, 1997; van Leeuwe et al, 1997; Takeda, 1998]. Arrigo and McClain [1994] used CZCS data to estimate primary production in the Ross Sea. Several studies combined CZCS data with satellitederived ice cover information to examine ice edge phytoplankton bloom dynamics [Sullivan et al, 1988; Comiso et al, 1990]

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