The buoyancy flux Bo at the air/sea interface is
very useful to understand the variability of the stratification of the mixed
layer, the oceanic mixing, the phytoplankton dynamics and then the coastal
upwelling. The atmospheric reanalysis ERA5 and the oceanic reanalysis ORAP5
data have been used in this study to describe the sea surface Bo and, its
influence on the variability of the mixing in the mixed layer and consequently
on the coastal upwelling along the northern coast of the Gulf of Guinea. The Bo
is negative along the coast and, is characterized by a seasonal variability
dominated by the thermal buoyancy flux. This study has also shown that the
mixing layer is very shallow along the coast and deeper offshore. The negative
value of the Bo increases the stratification of the mixed layer and reduces the
mixing. This could explain why the mixed layer is shallow in this region. This
work suggests that an increasing trend of the global warming could have
dramatic impact in this area by increasing the stratification in the mixed
layer and would contribute to reducing the coastal upwelling intensity.
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