Depth-integrated primary production in the eastern tropical and subtropical North Atlantic basin from ocean colour imagery

Abstract

Existing satellite numerical models and data interpolation methods were used to evaluate the scales of variation in the vertical distribution of the phytoplankton biomass and the daily rate of primary production within the subtropical and tropical NE Atlantic Ocean (5-40 N; 6-30 W). The choice of this area was dictated principally by its economical importance, as it represents a large fishing ground due to upwelling activities along the coast of Morocco and Mauritania. After geographical partition of the area of study into 'bio-geochemical provinces' based on bathymetry and surface circulation, up to 300 satellite scenes obtained from the defunct Coastal Zone Color Scanner (CZCS) and covering the full year 1983 were processed into maps of surface chlorophyll and were further analysed into integrated primary production. Analyses of satellite data included a specific method to account for the sensitivity loss of the sensor during the studied period. The results of the productivity model are presented in terms of seasonal variations in the daily and annual photosynthetic carbon production in the various provinces and their contribution to the productivity of the overall study area. A total of 0.82 GtC y-1 was computed for the subtropical and tropical NE Atlantic. One third of this is produced within the coastal zone although it accounts for only 14% of the total area.