A massive belt of sargassum seaweed, stretching an astonishing 5,000 miles across the Atlantic Ocean, has raised concerns among scientists and coastal communities alike. This vast swath of floating brown algae, known as the Great Atlantic Sargassum Belt (GASB), extends from the shores of West Africa all the way to the Gulf of Mexico, making it visible even from space.
Data collected via satellite revealed that in May 2026, the sargassum biomass reached a staggering 37.5 million metric tons across the Atlantic. Meanwhile, researchers from the University of South Florida (USF) documented 33.6 million metric tons in June within their monitored area of the Atlantic basin. These measurements indicate that 2026 could mark the second-largest year on record for sargassum accumulation.
The rapid emergence of this phenomenon is striking. Before 2010, the sargassum belt was nearly nonexistent, with only about 1 million metric tons recorded in 2011. By comparison, last year’s figures approached 40 million metric tons. Brian Barnes, a research assistant professor at USF’s College of Marine Science, explained to Reuters that the volume of sargassum appears to be doubling approximately every five years, highlighting an alarming and accelerating trend.
Origins and Drivers of the Expansion
Sargassum is a type of brown seaweed known for naturally forming floating mats, traditionally linked to the Sargasso Sea in the North Atlantic. However, starting around 2010, shifts in environmental conditions caused unusually strong winds to push sargassum mats into tropical waters off the coast of West Africa. This movement set in motion the formation of the expansive sargassum belt now spanning much of the Atlantic.
The proliferation of sargassum has significant implications for affected coastal regions, as the thick mats can disrupt marine ecosystems and impact tourism-dependent economies. As the phenomenon continues to evolve, ongoing monitoring and research remain crucial for understanding its drivers and mitigating its effects.