Why does the Guinea Current exist at all? There are no similar currents in the Pacific or Indian Oceans and the Guinea Current also disappear during northern summers. Why?
The Guinea Current is in geostrophic balance with isopycnals sloping upwards towards the north. The current is not directly related to wind direction and magnitude and that makes rather especial. As many other eastern boundary currents, it is characterized by the presence of coastal upwelling (Bakun, 1978), which delivers nutrients to the surface waters and results in increased primary production.
The Guinea Current is connected with the North Equatorial Counter Current (NECC) and in fact it can be considered the eastern continuation of the NECC. The seasonal variations in the position of the Intertropical Convergence Zone affect the connection between NECC and Guinea Currents. The Guinea Current is also connected to the Canary Current flowing southward along the African coast. In this sense, the Guinea Current is at least partially related to the Indian and Pacific Equatorial Counter Currents. The difference is that there is no long stretch of coast parallel to the Equator in those oceans.
Also, the Guinea Current does not disappear during the northern summer. In fact, there is a tendency for the current to intensify (check Figure 3 in Bakun, 1978 for instance).
- Bakun, A., 1978. Guinea current upwelling. Nature, 271(5641), pp.147-150.