Across the Caribbean, Gulf of Mexico, and West African coasts, massive arrivals of Sargassum seaweed have become an annual crisis. Thick mats of algae blanket beaches, disrupt fisheries, damage tourism, and release harmful gases as they decay, with cleanup costs reaching hundreds of millions of dollars each year. What began as an unexpected environmental phenomenon has grown into a persistent socio-economic challenge affecting multiple regions on both sides of the Atlantic.
A new study by international researchers, led by CMCC scientist Annalisa Bracco, now suggests that this growing problem could also represent an untapped opportunity. The research, "Changing Drivers of the Great Atlantic Sargassum Belt from Physical Forcing to Ecological Control," shows that the vast blooms of Sargassum are not only likely to persist, but may be predictable. This is significant because being able to predict blooms greatly increases our chances of using them for climate solutions such as marine carbon dioxide removal and biofuel production.
The so-called Great Atlantic Sargassum Belt appeared in 2011 and has since expanded into a transoceanic system stretching over 8,000 kilometers 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 this expansion has amplified its impacts on coastal communities, it also represents an enormous, naturally occurring pool of carbon captured through photosynthesis.
"Sargassum absorbs large amounts of carbon dioxide as it grows," explains 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 study reveals that the drivers behind Sargassum growth have fundamentally changed over time. In its early years, the expansion of the belt was primarily driven by physical processes, particularly stronger winter winds that deepened the ocean's mixed layer and brought nutrients to the surface. Over time, however, the system has evolved into a self-sustaining ecosystem. Sargassum hosts entire communities of marine organisms that recycle nutrients – especially nitrogen – within the floating mats, while decaying algae release additional nutrients back into the water. This internal ability to regenerate nitrogen has created a feedback loop that allows for growth even in the absence of wind events, and has become the dominant driver in recent years.
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 crucial step forward, as it reduces uncertainty about the future of the blooms and makes long-term planning feasible. The study also shows that the system is now largely self-sustaining through an internal ecological feedback, making natural decline unlikely and reinforcing the need for long-term management strategies.
The persistence and predictability of the Great Atlantic Sargassum Belt suggest opportunities to turn it from a burden into a resource, including offshore harvesting for deep-ocean carbon storage or conversion into biofuels and other materials, with potential benefits for emissions reduction and cleanup costs.
"It's a striking example of how the ocean can reorganize itself very quickly," says Bracco. "What started as a wind-driven event has become a self-sustaining biological system. The fact that we can now understand and predict it means we can also start thinking seriously about how to manage it."
The findings provide a scientific foundation for policymakers, investors, and coastal nations to explore long-term solutions that combine environmental protection with climate innovation.
More information:
Zhou, X., Novi, L., Hay, M.E. et al. Changing drivers of the Great Atlantic Sargassum Belt from physical forcing to ecological control. Nat Commun 17, 4600 (2026). https://doi.org/10.1038/s41467-026-72183-4
