Spatial variability in autumnal equatorial upwelling intensity within the Gulf of Guinea as inferred from in situ measurements

Type Article
Date 2019-03
Language English
Author(s) Nubi O. A.1, Oyatola O.O1, Bonou F2, 3
Affiliation(s) 1 : Nigerian Institute for Oceanography and Marine Research, Lagos, Nigeria.
2 : Institut de Recherches Halieutiques et Océanologique du Benin, (IRHOB), Cotonou-Bénin.
3 : Université Nationale des Sciences, Technologie, Ingénierie et Mathématiques(UNSTIM), Cotonou-Bénin
Source Journal of Oceanography and Marine Science (2141-2294) (Academic Journals), 2019-03 , Vol. 10 , N. 1 , P. 1-10
DOI 10.5897/JOMS2018.0146
Keyword(s) Vertical mixing, zonal advection, equatorial undercurrent, equatorial upwelling, Gulf of Guinea, nutrients, phytoplankton biomass, surface enrichment.

In attempt to study the spatial differences in autumnal equatorial upwelling intensity relative to bio-productivity in the eastern equatorial Atlantic, oceanographic in situ data along regions 10°W, 0°E, 2.5°E and 6°E, collected in the Gulf of Guinea during autumn cruise carried out in September 2007 were analyzed. The surface mean values for temperature along 10°W, 0°E, 2.5°E and 6°E are 25.02, 26.15, 26.88 and 25.60°C, respectively. There was eastward weakening of the equatorial undercurrent from 10°W until its complete disappearance at 6°E. The highest concentration of nitrate recorded at the surface at 10°W was attributed to the shoaling pycnocline observed at this region. The surface mean values for nitrate along 10°W, 0°E, 2.5°E and 6°E are 0.37, 0.09, 0.04 and 0.04 μ, respectively. In response to the shoaling pycnocline at 10°W, corresponding to the highest concentration of chlorophyll fluorescence was recorded at this region. The surface mean values for chlorophyll fluorescence along 10°W, 0°E, 2.5°E and 6°E are 0.34, 0.05, 0.07 and 0.08 mg/m3, respectively. Contributions to equatorial upwelling by the equatorial undercurrent were the strongest and mostly expressed along 10°W. Profiles for apparent oxygen utilization and chlorophyll fluorescence gave indications that biological response to surface enrichments within the equatorial bands was highest at region 10°W. Vertical sections for studied parameters were unsuggestive of westward advection from 6°E to 10°W within the equatorial band, and this signifies the important role of vertical processes in equatorial enrichment at 10°W during boreal autumn.

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