Nutrient Cycling Drives Atlantic Sargassum Growth
Researchers identify land-based runoff and internal nutrient recycling as key drivers of the Great Atlantic Sargassum Belt.
Updated on Oct. 26, 2026 in Environmental
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Scientists have determined that the massive accumulation of seaweed in the Atlantic Ocean is fueled by increased nutrient levels and natural recycling processes. As of May 2025, satellites tracked approximately 37.5 million metric tons of sargassum across the region.
Why it matters
Understanding the drivers of sargassum proliferation is essential for managing its ecological impact on coastal regions. The seaweed, which produces hydrogen sulfide gas upon decomposition, is simultaneously a critical habitat for marine life.
Sargassum biomass is capable of doubling in 11 days under nutrient-rich conditions. Tissue analysis reveals a 55% increase in nitrogen content alongside a 50% rise in the nitrogen-to-phosphorus ratio since the 1980s.
The players
National Oceanic and Atmospheric Administration
This federal agency is responsible for designating sargassum as Essential Fish Habitat due to its role in supporting marine biodiversity.
The details
The massive belt, which first appeared in satellite records in 2011, recruits nutrients from land-based runoff, wastewater discharge, and atmospheric deposition. Within the floating mats, microbial breakdown and animal excretions further provide recycled nutrients that sustain the ecosystem.
Timeline
1980s-2020s: Nitrogen content in sargassum tissue increased by 55%.
2009-2010: A negative phase of the North Atlantic Oscillation occurred.
2011: The Great Atlantic Sargassum Belt first appeared in satellite records.
May 2025: Satellites captured 37.5 million metric tons of sargassum.
September 2026: Sargassum biomass fell by half from August levels.
The Big Picture
This study shifts our understanding of sargassum from a purely oceanic phenomenon to a cycle heavily influenced by terrestrial nutrient inputs. It updates the legacy hypothesis that seaweed blooms were driven primarily by isolated ocean currents.
The study suggests that future coastal management strategies may need to prioritize land-based nutrient reduction to control biomass growth. Effective management could lead to fewer beach closures caused by decomposing seaweed and the associated release of hydrogen sulfide gas.
The takeaway
Management of sargassum requires a dual approach that respects its status as a vital marine habitat while mitigating the nuisance of beach accumulations. By monitoring nutrient influxes, researchers hope to better predict the size and impact of future seaweed blooms.
Further reading
Learn more about the Environmental factors impacting ocean health.
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Should your local government increase regulations on agricultural runoff to help reduce coastal seaweed blooms?
