A new study shows how Atlantic seaweed could power carbon dioxide removal and biofuel production
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Spanning the Caribbean, Gulf of Mexico and West African coasts, large quantities of Sargassum seaweed have become a persistent socio-economic challenge. Thick mats of algae cover beaches, disrupt fisheries, harm tourism and release damaging gases as they decay. Both sides of the Atlantic are coming into contact with thick amounts of algae, with clean-up costs spiralling into hundreds of millions of dollars every year.
However, a new study by international researchers suggests that behind the growing problem could be an untapped opportunity. The research, which examined the Great Atlantic Sargassum Belt, shows that Sargassum prevalence can be predicted. This is significant because the ability to predict Sargassum blooms greatly increases the likelihood of using them for climate solutions, such as marine carbon dioxide removal or biofuel production.
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The Great Atlantic Sargassum Belt has expanded since its formation in 2011 to stretch across 8,000 km from West Africa to the Caribbean. By 2025, its biomass exceeded 37 million tons – about six times the total body mass of Italy’s population. While the expansion has heightened its impacts on coastal communities, it also represents a significant, naturally occurring pool of carbon captured through photosynthesis.
Using a model based on satellite observations and oceanographic data, the researchers reconstructed Sargassum variability from 2011 to 2022 and successfully predicted concentrations for 2023 and 2024. This predictive capability is a vital step forward because it reduces the scope of uncertainty surrounding the future of the blooms and improves the feasibility of long-term planning.
‘Sargassum absorbs large amounts of carbon dioxide as it grows,’ said the leader of the study and CMCC scientist, Annalisa Bracco. ‘The key challenge is that when it reaches the coast and decomposes, much of that carbon is released back into the atmosphere. If we can intervene before this happens, this system could instead be part of the solution.’
The persistence and predictability of the Great Atlantic Sargassum Belt suggest opportunities to transform it from a challenging environmental phenomenon into one that creates opportunity. For example, offshore harvesting for deep-ocean carbon storage or conversion into biofuels and other materials is a potential approach that has benefits for emissions reductions and clean-up costs.
The study reveals that the drivers behind the growth of Sargassum have fundamentally changed over time. In its early years, physical processes largely drove the expansion of the belt. This particularly occurred through stronger winter winds that deepened the ocean’s mixed layer and brought nutrients to the surface.
Over time, the system has evolved into a self-sustaining ecosystem. Entire communities of marine organisms are hosted throughout the belt. These organisms recycle nutrients – especially nitrogen – within the floating mats. Meanwhile, decaying algae release additional nutrients back into the water.
