Projected Amazon forest loss alters tropical Atlantic circulation and surface heat exchange through reduced freshwater input

Deforestation alters the terrestrial water cycle, with consequences that can extend to the ocean. In the Amazon Basin, projected forest loss is expected to substantially modify river discharge, yet how these hydrological changes affect tropical ocean circulation and surface heat exchange remains poorly understood. Here we ran an offline hydrological simulation with the MGB (Modelo de Grandes Bacias, or Large-Basin Model) to produce river outflow for a business-as-usual deforestation scenario projected for 2050, that was fed into the Regional Ocean Modeling System (ROMS) to simulate the ocean for the period 1992–2015. This setup isolates the influence of changes in freshwater export on the western tropical North Atlantic. Simulations of a business-as-usual 2050 scenario (~ 45% forest loss) show dry-season discharge reductions exceeding 50% in southern tributaries and ~ 12% at Óbidos, increasing surface salinity and reorganizing the Amazon River plume. These changes intensify the North Brazil Current and its retroflection by ~ 14%, deepen the mixed layer by up to ~ 6 m, thin the barrier layer by up to ~ 8 m, and alter surface heat exchange, warming the surface by up to 0.4 °C along the retroflection and North Equatorial Countercurrent corridor during boreal summer and autumn. Sustained Amazon forest loss can therefore drive persistent changes in the upper-ocean circulation and heat distribution of the tropical Atlantic.