FISHERY BULLETIN: VOL. 84, NO. 3 



prisingly similar to the shape of the maximum of 

 cloudiness in September 1982, derived from satellite 

 measurements of outgoing long wave radiation (Gill 

 and Rasmusson 1983). Similarity might be causal, 

 i.e., high SSCC values might result from a response 

 of the phytoplankton to attenuation of light by the 

 clouds, or from enhanced phytoplankton growth 

 caused by precipitation of dust and aerosols by the 

 rain (Menzel and Spaeth 1962). It may also result, 

 at least partly, from sampling artifacts. 



The major features shown by this SSCC monitor- 

 ing experiment are in agreement with the large- 

 scale processes that affect the tropical Pacific dur- 

 ing El Nino episodes. The collapse of the equatorial 

 upwelling in October 1982 resulted in a nearly com- 

 plete disappearance of the chlorophyll-rich area 

 which is usually located across the Equator. A 

 moderate enrichment persisted, however, east of 

 long. 120°W. In the northwestern tropical Pacific, 

 the eastward drift of the warmwater pool was 

 followed by conditions which stimulated photosyn- 

 thesis: a shallower thermocline, and more light 

 penetrating to the nutrients gave rise to unusually 

 high chlorophyll concentrations west of 180° from 

 October 1982 to March 1983. In April-June 1983, 

 the equatorial upwelling in the eastern Pacific was 

 still reduced by the El Nino conditions, and the 

 enrichment in the northwestern tropical Pacific was 

 less intense; during this period, low chlorophyll con- 

 centrations prevailed over most of the tropical 

 Pacific. 



ACKNOWLEDGMENTS 



I would like to thank Henri Walico for the 

 thousands of chlorophyll measurements which are 

 the basis of the present work. I am indebted to the 

 captains and crews of the merchant ships who call 

 at Noumea for kindly and carefully sampling and 

 filtering at sea. 



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