Sargassum transport to the Amazon Coast: Explaining the stranding through meteorological and oceanographic conditions

Over the recent years, different areas around the tropical Atlantic Ocean experienced an increase in pelagic Sargassum stranding events. Such incidents pose ecological and socioeconomic challenges, since they are difficult to predict and can impact coastal communities. In this study, we investigate the physical mechanisms behind Sargassum stranding events on the Brazilian Amazon Coast, focusing on the northeastern Pará region (northern Brazil), especially during the sporadic massive events registered in May 2014, April 2015, March 2019 and March 2025. We used a combination of observational data, reanalysis, forecast products, and Lagrangian experiments to explore the role of meteorological and oceanographic conditions during the occurrence of the strandings. Our results suggest that the events are related to the rainy season, when the Intertropical Convergence Zone (ITCZ) is positioned at its southernmost extent, bringing intense rainfall and northeasterly winds to the region. These winds can increase the landward transport of floating particles into the Amazon Continental Shelf (ACS). The results from the Lagrangian simulations highlighted the importance of wind drag and local processes (i.e., tidal currents and Stokes drift) in promoting the intrusion of floating particles into the inner shelf, particularly in the northeastern sector of the ACS, which emerges as a preferential pathway for the entrance of offshore Sargassum patches. This pathway was also highlighted by the sighting of Sargassum close to this area prior to the massive event of 2025, reinforcing the role of winds and tidal currents in connecting the northeastern offshore sector of ACS to the coast. While global reanalysis products and forecast systems provided valuable insights, future research should focus on the implementation of regional models to provide more accurate predictions near the coast, improving predictive capabilities to mitigate the impacts of these phenomena.