Gulf of Guinea upwelling

Gulf of Guinea upwelling
Name	Gulf of Guinea upwelling
Location	Gulf of Guinea, Atlantic Ocean
Coordinates	0°–10°N, 0°–10°E
Type	Coastal upwelling system
Countries	Nigeria; Ghana; Ivory Coast; Togo; Benin; Cameroon; Equatorial Guinea; Gabon
Area	~200,000 km² (variable)
Primary forcing	Trade winds; Equatorial Atlantic dynamics
Dominant species	Sardinella aurita; Sardinella maderensis; Thunnus albacares

Gulf of Guinea upwelling

The Gulf of Guinea upwelling is a regional coastal and equatorial upwelling system off the western coast of Africa centered near the Equator and extending from the Ivory Coast to Gabon. It produces marked seasonal and interannual variability in sea surface temperature, nutrient supply, and primary productivity that influence the marine ecosystems exploited by nations such as Nigeria, Ghana, and Cameroon. The upwelling interacts with larger-scale features including the Benguela Current, the North Brazil Current, and the Intertropical Convergence Zone.

Overview and Physical Setting

The upwelling occupies coastal shelves and the near-equatorial Atlantic margin adjacent to the Gulf of Guinea basin, bounded to the west by the Accra Plain and to the south by the Congo River outflow region. Bathymetric controls include the Sierra Leone Rise and submerged banks that modulate cross-shelf exchange, while riverine inputs from the Volta River and Niger River influence salinity stratification. The region sits beneath the seasonal migration of the Intertropical Convergence Zone and is overlain by air masses associated with the African Easterly Jet and the South Atlantic Anticyclone.

Mechanisms and Seasonal Variability

Upwelling results from wind-driven Ekman transport associated with the seasonal reversal of trade winds linked to the migration of the Intertropical Convergence Zone and the monsoonal pulse of the West African Monsoon. During boreal summer, northeasterly winds enhance coastal upwelling off Senegal and extend eastward toward Ghana and Togo, while boreal winter conditions shift wind stress and favor equatorial upwelling near the Gabon and Gulf of Guinea equatorward region. Remote forcing from equatorial Kelvin and Rossby waves generated near the Equatorial Atlantic adjusts thermocline depth, and episodic intraseasonal events associated with the Madden–Julian Oscillation modulate intensity.

Oceanographic and Atmospheric Controls

Key oceanographic controls include the position and strength of the Atlantic Meridional Overturning Circulation branches in the eastern basin, variability in the North Equatorial Countercurrent, and mesoscale eddies shed by the Northeast Brazil Shelf and Cabo Verde Basin. Atmospheric controls derive from the seasonal modulation of the South Atlantic Convergence Zone and teleconnections with the El Niño–Southern Oscillation and the North Atlantic Oscillation, which influence trade wind strength. Interactions with river plumes from the Niger Delta and the Congo Basin produce horizontal density gradients that can enhance or suppress local upwelling through buoyancy-driven currents.

Biological Productivity and Ecosystem Impacts

Nutrient entrainment from deep, nutrient-rich waters sustains high primary productivity dominated by diatoms and dinoflagellates, which support productive pelagic food webs including exploited stocks of Sardinella aurita, Sardinella maderensis, Trachurus trachurus-like assemblages, and tunas such as Yellowfin tuna (Thunnus albacares) and Skipjack tuna (Katsuwonus pelamis). Seasonal phytoplankton blooms drive secondary production supporting marine mammals like the Atlantic humpback dolphin and demersal communities on upwelling-influenced shelves. Hypoxic and low-oxygen zones can develop in stratified conditions, affecting benthic habitats and mobile species including sharks and sea turtles such as the Olive Ridley sea turtle.

Socioeconomic and Fisheries Implications

Coastal fisheries in Ivory Coast, Ghana, Benin, and Nigeria rely on upwelling-enhanced stocks of small pelagics and tuna, underpinning livelihoods in artisanal fleets operating from ports like Tema and Lagos. Commercial purse seine and industrial trawl operations target migratory tuna associated with upwelling fronts, engaging companies and institutions linked to regional fisheries governance such as the Sub-Regional Fisheries Commission (SRFC) and the Economic Community of West African States (ECOWAS). Upwelling variability influences food security, export earnings, and socio-political issues in coastal communities, intersecting with management frameworks like the Port State Measures Agreement and regional observer programs coordinated with the Food and Agriculture Organization.

Observations, Monitoring, and Modeling

Monitoring employs satellite remote sensing platforms including TOPEX/Poseidon and modern altimetry missions, sea surface temperature retrievals from Aqua and Terra, and ocean color sensors used by institutions such as the European Space Agency and National Aeronautics and Space Administration. In situ arrays include moorings from programs coordinated with the National Oceanic and Atmospheric Administration and research cruises by institutions like the Institut de Recherche pour le Développement and Woods Hole Oceanographic Institution. Numerical modeling efforts use regional implementations of general circulation models coupled with ecosystem modules from frameworks developed at NOAA Geophysical Fluid Dynamics Laboratory and the Centre National de Recherches Météorologiques, integrating data assimilation from projects like ARGO and the Global Ocean Observing System.

Category:Oceanography Category:Upwelling systems Category:Gulf of Guinea