Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7142
Title: Primary organic production and standing stock of zooplankton in the tropical Atlantic Ocean—Equalant I and II
Author: Conrad V. W. Mahnken
Publication Year: 1969
Journal: Bulletin of Marine Science
Volume: 19
Issue: 3
Pages: 550-567

Primary productivity (C14 method) and standing stock of zooplankton (oblique ICITA net tows) were measured during Equalant expeditions I (January–March, 1963) and II (July–September, 1963) in the tropical Atlantic Ocean.  The seasonal distributions of these variables are correlated with the prevailing conditions of the physicochemical environment.  Four areas of biological enrichment are distinct within the surveyed area, from 20°N to 20°S latitude.

Two of these areas are relatively near the shores from Senegal to Liberia, and Gabon to the Congo.  Both areas have oceanographic thermal fronts that migrate north during July and August, and south during February and March.  Both regions go through a seasonal cycle of enrichment.

A third region showing high rates of carbon fixation is the coast of Ghana and Ivory Coast, during July and August.  The high rates of carbon fixation coincide with the period of maximum seasonal upwelling.

A zonal belt that extends from the African coast to the South American coast at the equator constitutes the fourth area of enrichment.  Variations in carbon fixation and abundance of zooplankton are caused by seasonal changes in the oceanography.  Values are highest for carbon fixation and abundance of zooplankton during July and August when a thermal anticline is situated near the equator.  During February and March, the meridional distribution of temperature is relatively uniform and enrichment is less.  

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