Climates in Africa and South America are closely linked to the tropical Atlantic Ocean, associated with the intense rainfall of the Intertropical Convergence Zone (ITCZ), which extends from South America to North Africa. This rainfall occurs over some of the warmest surface waters, where the trade winds from the Northern and Southern Hemispheres converge. These winds drive the upwelling of cold, nutrient-rich waters—highly productive—in the eastern equatorial Atlantic, in the Benguela region, and along the coast of West Africa. Strong seasonal variations in rainfall, winds, and oceanic conditions are linked to the West African and South American monsoons. The tropical Atlantic is also subject to intense cyclonic activity in the western basin, and it receives inputs from some of the world’s largest rivers, directly affecting oceanic conditions. Understanding, monitoring, and predicting surface exchanges and ocean transport are therefore essential to improve forecasts, anticipate ecosystem changes, and support the health, food security, and economies of bordering countries.
One of the specific features is that the tropical Atlantic exhibits pronounced variability on interannual to multidecadal timescales, driven by both natural processes and anthropogenic forcing. Atlantic multidecadal variability strongly modulates equatorial Atlantic interannual dynamics and exerts remote influence on the tropical Pacific. Interannual variability is mainly described by two climate modes: the Atlantic Zonal Mode, linked to sea surface temperature (SST) anomalies near the equator and peaking in the eastern part and the Atlantic Meridional Mode characterized by a cross-equatorial gradient of SST and wind anomalies. These low-frequency variations have profound consequences for regional climate, including rainfall and drought over adjacent continents, as well as for upper ocean biogeochemistry and marine ecosystems. Sustained observations are essential, not only to constrain models and improve decadal prediction, but also to distinguish internal variability from climate change.
Over the last three decades, the key scientific questions in the Tropical Atlantic have centered on:
- What are the main modes of climate variability in the Tropical Atlantic and their driving processes?
- Can these fluctuations be reliably forecast, and which processes must models accurately capture?
- How does Tropical Atlantic variability impact on upper-ocean biogeochemistry and ecosystems?
