Nutrient Drivers Behind Massive Atlantic Seaweed Belt Found
New research identifies how internal nutrient recycling and runoff fuel the 37.5 million metric ton sargassum accumulation.
Updated on Oct. 26, 2026 in Environmental
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Researchers have identified nutrient recycling and subsurface oceanic sources as the primary drivers behind the Great Atlantic Sargassum Belt. This massive accumulation of floating seaweed, which first appeared in satellite records in 2011, currently contains approximately 37.5 million metric tons of biomass.
Why it matters
Understanding the nutrient drivers of sargassum is essential for managing its impact on coastal ecosystems and the public. As sargassum decomposes on beaches, it releases hydrogen sulfide gas, creating environmental and health challenges for communities throughout the Atlantic, Caribbean, and Gulf of Mexico.
Sargassum biomass can double in just 11 days when provided with nutrient-rich conditions. Researchers found that internal nutrient recycling via microbial breakdown and animal excretions within the mats helps sustain the belt's rapid growth.
The players
National Oceanic and Atmospheric Administration
A federal agency that monitors ocean and atmospheric health and manages protected marine habitats.
The details
The belt thrives by leveraging elevated levels of nitrogen and phosphorus. These nutrients originate from a combination of land-based runoff, wastewater discharge, and atmospheric deposition, which are then recycled within the structure of the seaweed mats themselves. While the National Oceanic and Atmospheric Administration designates sargassum as Essential Fish Habitat—a critical area for fish spawning and growth—the excessive accumulation causes significant decay upon reaching coastal shorelines.
Timeline
2009-2010: Negative phase of the North Atlantic Oscillation occurred.
2011: The Great Atlantic Sargassum Belt first appeared in satellite records.
1980s-2020s: Nitrogen content in sargassum tissue increased by 55%.
May 2025: Satellites measured 37.5 million metric tons of sargassum.
September 2026: Sargassum biomass fell by half from the previous month.
The Tech Race
This research clarifies the growth dynamics of the Great Atlantic Sargassum Belt, which has expanded significantly since its initial 2011 discovery. It builds on satellite monitoring efforts to move from simple observation to identifying the specific nutrient inputs fueling the surge.
Coastal communities in the Caribbean and along the Gulf of Mexico must manage the persistent arrival of massive seaweed mats that release hydrogen sulfide gas when they rot. Local authorities continue to track these floating fields to predict beach accumulation events.
The takeaway
The rapid doubling time of sargassum biomass in nutrient-rich water underscores why reducing land-based runoff remains the primary strategy for limiting the belt's scale. Watch for updated nitrogen-to-phosphorus ratio data in future reports to confirm if nutrient mitigation efforts are curbing growth rates.
Further reading
Learn more about the shifting oceanic landscape in our Environmental section.
Source note: This article includes information reported by ZME Science.
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Should your local government increase regulations on agricultural runoff to help reduce coastal seaweed blooms?
