NASA's PACE satellite has mapped a massive proliferation of Sargassum seaweed in the tropical Atlantic, with record-high levels recorded in the Caribbean and Gulf of Mexico in June 2026.
Key facts
- •The Great Atlantic Sargassum Belt saw its 2026 peak in June, ranking as the second-highest year in the satellite record.
- •The Gulf of Mexico reached 5 million metric tons of Sargassum in June 2026, nearly double its previous record.
- •Sargassum biomass in the Atlantic has been increasing since 2011, with total amounts more than doubling every five years.
- •NASA’s PACE satellite, launched in February 2024, is now used to generate near-real-time Sargassum maps.
- •Decomposing Sargassum on beaches releases hydrogen sulfide, which creates a rotten-egg smell and can impact local tourism.
Data from the Ocean Color Instrument (OCI) on NASA’s PACE satellite shows that the Great Atlantic Sargassum Belt reached its annual peak in June 2026. This brown floating algae has shifted its range since 2011, thinning in the North Atlantic while proliferating in the tropical Atlantic. The 2026 season marks the second-highest abundance in the satellite record, trailing only 2025.
By the numbers
Regional Impact and Record Levels
According to the University of South Florida (USF) College of Marine Science, the Caribbean Sea and the Gulf of Mexico both experienced record-high amounts of Sargassum in June 2026. The western Caribbean contained 3.6 million metric tons, while the eastern Caribbean held 9 million metric tons. The Gulf of Mexico reached 5 million metric tons, nearly doubling its previous record set in 2025.
Ecological and Environmental Effects
While Sargassum provides habitat for marine life and produces oxygen in open ocean environments, large accumulations near shore can be detrimental. Excessive mats can suffocate corals and seagrasses, and decomposing seaweed on beaches releases hydrogen sulfide, a gas that poses risks to both tourism and local ecosystems. Scientists at USF use satellite tracking to help communities monitor the extent of these mats and prepare for potential inundation.
Technological Advancements in Monitoring
The OCI sensor on the PACE satellite, launched in February 2024, provides enhanced sensitivity and hyperspectral capabilities for monitoring the belt. This allows researchers to distinguish Sargassum from other floating algae like Trichodesmium with greater accuracy. These observations supplement long-term data from the MODIS and VIIRS sensors, which have tracked the belt's growth since 2011. Researchers believe the ongoing increase in biomass may be linked to ocean warming and nutrient availability.
Timeline
- March 2000The continuous MODIS satellite record for tracking Sargassum biomass begins.
- 2011The Great Atlantic Sargassum Belt begins its development and range shift.
- February 2024NASA launches the PACE satellite to monitor ocean ecosystems.
- July 2025The record high for Sargassum biomass is set.
- June 2026Sargassum reaches its annual peak, marking the second-highest year on record.
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This article was independently rewritten by ManyPress editorial AI from reporting originally published by NASA Breaking News.
