The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, and forcing processes. This knowledge gap is addressed in two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic. Part 1 is concerned with the circulation over the West African continental slope at the southernmost reach of the Canary Current system, between ∼ 8 and 20° N. The focus is on the depth range most directly implicated in the wind-driven circulation (offshore and coastal upwellings and Sverdrup transport) located above the potential density σ_t = 26.7 kg m⁻³ in the model (approx. above 250 m of depth). In this sector and for this depth range, the flow is predominantly poleward as a direct consequence of positive wind stress curl forcing, but the degree to which the magnitude of the upper ocean poleward transport reflects Sverdrup theory varies with latitude. The model poleward flow also exhibits a marked semiannual cycle with transport maxima in spring and fall. Dynamical rationalizations of these characteristics are offered in terms of wind forcing of coastal trapped waves and Rossby wave dynamics. Remote forcing by seasonal fluctuations of coastal winds in the Gulf of Guinea plays an instrumental role in the fall intensification of the poleward flow. The spring intensification appears to be related to wind fluctuations taking place at shorter distances north of the Gulf of Guinea entrance and also locally. Rossby wave activity accompanying the semiannual fluctuations of the poleward flow in the coastal waveguide varies greatly with latitude, which in turn exerts a major influence on the vertical structure of the poleward flow. Although the realism of the model West African boundary currents is difficult to determine precisely, the present in-depth investigation provides a renewed framework for future observational programs in the region.

Marine heatwaves (MHWs) cause significant harm to marine life and ecosystem services, and can intensify hurricanes. Global warming has increased the duration and intensity of MHWs over the last century, and permanent MHWs have been predicted in many areas of the ocean by the end of the 21st century. Climate interventions, such as stratospheric aerosol injection (SAI), have been proposed to reduce the mean global temperature; however, their potential impact on MHWs is unclear. In this study, we used the output from the Community Earth System Model to quantify MHWs under multiple time frames and climate change scenarios. We evaluated global MHW properties, including duration and maximum intensity—the maximum exceedance above the climatology—over historical (1990-2009), present (2015-2034), and future (2050-2069) periods. We analyzed output from two SAI scenarios aimed to maintain global mean surface temperatures at ∼1.5 and ∼1.0°C above pre-industrial levels (ARISE-SAI-1.5 and ARISE-SAI-1.0) and one non-SAI scenario (SSP2-4.5). Our results show that despite the SAI reducing the global average maximum intensity and duration of MHWs relative to SSP2-4.5, the magnitude of the effects varies spatially. Compared with the present climate, SAI scenarios would reduce MHW intensity in 25-76% of the ocean and MHW duration in 21-80% of the ocean. The largest future reductions in maximum intensity and duration occurred in the coastal regions of the Tropical Atlantic, Indian, Arctic, and South Atlantic oceans. Even with a more aggressive SAI scenario (ARISE-SAI-1.0), nearly 25% of the ocean would remain unaffected, with areas like the North Atlantic, Tropical Pacific, and parts of the Southern Oceans still experiencing more intense and longer MHWs, meaning that SAI could be perceived locally as ineffective at mitigating MHW even while the global mean temperature target is being met.

The West African seaboard is one of the upwelling sectors that has received the least attention and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, forcing processes. This knowledge gap is addressed in a suite of two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic. Part 1 is concerned with the circulation over the West African continental slope at the outmost reach of the Canary current system, between ∼ 10 and 20° N. The focus is on the depth range most directly implicated in the wind-driven circulation (offshore/coastal upwellings and Sverdrup transport), located above the potential density σ_t = 26.7 kg m⁻³ in the model (approx. above 250 m depth). In this sector and for this depth range, the flow is predominantly poleward as a direct consequence of positive wind stress curl forcing, but the degree to which the magnitude of the upper ocean poleward transport reflects Sverdrup theory varies with latitude. The model poleward flow also exhibits a marked semi-annual cycle with transport maxima in spring and fall. Dynamical rationalizations of these characteristics are offered in terms of wind forcing of coastal trapped waves and Rossby wave dynamics. Remote forcing by seasonal fluctuations of coastal winds in the Guinea Gulf play an instrumental role in the fall intensification of the poleward flow. The spring intensification appears to be related to wind fluctuations taking place at shorter distances, north of the Guinea Gulf entrance and also locally. Rossby wave activity accompanying the semi-annual fluctuations of the poleward flow in the coastal wave guide varies greatly with latitude, which in turn, exerts a major influence on the vertical structure of the poleward flow. Although the realism of the model West African boundary currents is difficult to determine precisely, the present in-depth investigation provides a renewed framework for future observational programs in the region.

Recent offshore hydrocarbon discoveries along the Senegalese–Mauritanian margin increase the need to quantify oil-spill risk under the highly dynamic circulation of the southern Canary Current upwelling system. We investigate seasonal pollutant dispersion along the Senegalese Grande Côte using Lagrangian particle-tracking experiments forced by outputs from the open-source hydrodynamical ocean model CROCO. The analysis focuses on the role of wind-driven circulation, Ekman transport, and upwelling variability in controlling cross-shore and alongshore transport pathways. Results show a strong seasonal coastal circulation variability. During the cold season (January–May), intensified northerly winds drive coastal upwelling and offshore Ekman transport, enhancing divergence of surface currents and promoting the export of particles away from the coast. This regime limits particle nearshore accumulation but favors broader offshore dispersion over the continental shelf. In contrast, during the warm season (June–September), weakened upwelling-favorable winds and the establishment of anticyclonic circulation north of the Cape induce onshore transport and coastal retention. Particle-release experiments reveal enhanced trapping and accumulation along the Grande Côte during this period. The Kayar region and the Cape Verde Peninsula exhibit relatively higher pollutant exposure during the cold season, whereas the inner continental shelf along the Grande Côte becomes particularly vulnerable during the warm season. These findings suggest that seasonal wind forcing and associated Ekman dynamics have a significant influence on the trajectories of oil spills. Incorporating this variability into contingency planning is essential, as the inner continental shelf of the Senegalese Grande Côte is a dynamically sensitive, high-exposure zone under the warm-season circulation regime.

Recent offshore hydrocarbon discoveries along the Senegalese–Mauritanian margin increase the need to quantify oil-spill risk under the highly dynamic circulation of the southern Canary Current upwelling system. We investigate seasonal pollutant dispersion along the Senegalese Grande Côte using Lagrangian particle-tracking experiments forced by CROCO ocean model outputs. The analysis focuses on the role of wind-driven circulation, Ekman transport, and upwelling variability in controlling cross-shore and alongshore transport pathways. Results show a strong seasonal contrast. During the cold season (January–May), intensified northerly winds drive coastal upwelling and offshore Ekman transport, enhancing surface divergence and promoting the export of particles away from the coast. This regime limits nearshore accumulation but favors broader offshore dispersion over the continental shelf. In contrast, during the warm season (June–September), weakened upwelling-favorable winds and the establishment of anticyclonic circulation north of the Cape induce onshore transport and coastal retention. Particle-release experiments reveal enhanced trapping and accumulation along the Grande Côte during this period. The Kayar region and the Cape Verde Peninsula exhibit relatively higher exposure during the cold season, whereas the inner shelf along the Grande Côte becomes particularly vulnerable during the warm season. These findings demonstrate that seasonal wind forcing and associated Ekman dynamics exert first-order control on oil-spill pathways. Incorporating this variability into contingency planning is essential, as the inner continental shelf of the Senegalese Grande Côte is a dynamically sensitive, high-risk zone under the warm-season circulation regime.