On the nutrient distribution and phytoplankton biomass in the Gulf of Guinea equatorial band as inferred from in-situ measurements
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Abstract
Oceanographic in situ data collected in the Gulf of Guinea during six cruises carried out between 2005
and 2007 were analysed to study the influence of equatorial upwelling on the productivity of the region.
At 10°W, observations during boreal summer and autumn cruises captured seasonal upwelling
influences. In response to the shoaling pycnocline in June 2005, higher concentrations of nitrate and
chlorophyll fluorescence were recorded at the ocean surface in June than in September. Our findings
challenge the paradigm that westward advection from the nutrient-rich African coast is responsible for
equatorial enrichment in the Gulf of Guinea. Vertical sections of the parameters under study in the
summer of 2005 showed no westward advection from 3°E to 10°W within the equatorial band. This
emphasizes the important role of vertical processes in equatorial enrichment at 10°W. An additional
aspect of our study provides evidence of the impact on nutrient and chlorophyll distribution of offequatorial
westward recirculation of equatorial undercurrent waters (observed between 2°and 3°S)