Influence of the remote equatorial dynamics on the interannual variability along the northern coast of the Gulf of Guinea

This study explores the oceanic connection between the equatorial dynamics and the coastal variability along the northern coast of the Gulf of Guinea on interannual timescales, based on experiments with a high-resolution tropical Atlantic Ocean model over 1958-2015. Equatorial Kelvin waves, forced by wind-stress anomalies in the west-central equatorial basin, significantly control the interannual fluctuations of the coastal sea-level and subsurface temperature near the thermocline (>70%), leaving only a marginal role for the local forcing contribution. The dynamical coastal response exhibits a clear propagative nature, with poleward propagations (0.75-1.2 m.s^-1) from Cameroon to Liberia. Because the northern coast of the Gulf of Guinea is close to the equatorial waveguide, the coastal variability is influenced by both equatorially-forced coastal trapped waves and reflected equatorial Rossby waves. Furthermore, remote equatorial forcing explains more of the surface temperature variance for the coastal systems associated with clear upwelling characteristics such as Côte d’Ivoire and Ghana, where subsurface/surface coupling is more efficient. The surface thermal amplitude and timing is shaped by the coastal stratification and circulation and exhibits a marked seasonal modulation, so that the timing of the SST anomalies relative to the dynamical signature lacks consistency, making SST a less reliable variable for tracking coastal propagations in the Gulf of Guinea. Our findings open the possibility of predicting interannual changes in coastal conditions off Côte d’Ivoire and Ghana a few months in advance, to anticipate impacts on fish habitats and resources, and to facilitate proactive measures for sustainable management and conservation efforts.