Abstract
Inundations of pelagic Sargassum plague the tropical Atlantic, with size and impacts steadily increasing to surpass 30 million tons in 2025. Understanding the drivers of Sargassum growth in the so-called Great Atlantic Sargassum Belt is fundamental to developing effective mitigation strategies for affected nations. We present a nonlinear regression model that both explains the seasonal and interannual variability observed between 2011 and 2022 and predicts Sargassum concentrations in 2023 and 2024. The growth of Sargassum, initiated by a prolonged negative phase of the North Atlantic Oscillation, is initially enhanced through winter mixed layer deepening in response to stronger winds. An additional overlooked driver is the recycling of nutrients within the mixed layer, carried out by the community of organisms associated with Sargassum and aging Sargassum mats. This contribution increases over time to become dominant in recent years, offsetting the increase in stratification in 2023 and 2024.
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Data availability
Sargassum biomass data until 2022 have been extracted from ref. 38, using the manual extraction option of the online version of WebPlotDigitizer (https://automeris.io/WebPlotDigitizer.html, WebPlotDigitizer version 4.7, 2024), available at https://automeris.io/WebPlotDigitizer.html. Concentrations data for 2023 and 2024 were provided by Julien Jouanno, calculated from the raw images following the procedure detailed in ref. 3 and are available at https://zenodo.org/records/19004539. The Nitrogen isotopic composition data presented in Fig. 3 are available as xls file at https://doi.org/10.5281/zenodo.19076636. Source data are provided with this paper.
Code availability
All codes developed for this work are available on Zenodo at https://doi.org/10.5281/zenodo.19076636. See README and reproduce.docx files for a complete description of the code’s functionality.
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Acknowledgements
We thank the Google.org/Tides Foundation Grant TF2308-115588 for funding our work (grant to A.B.), Dr. Julien Jouanno for providing the Sargassum biomass concentration data for years 2023 and 2024, and David A. Montoya for contributing to the schematic in Fig. 3 and Fig. 5.
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A.B. conceived the project and wrote the paper together with X.Z.; X.Z. and L.N. developed the regression models and performed analysis and simulations, contributing equally. J.P.M., M.E.H., and A.B. collected the nutrient data; J.P.M. analyzed them and performed isotopic composition analysis. M.J.R. and A.A. contributed to the data interpretation. All authors contributed to the discussion and the final version of the paper.
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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 (2026). https://doi.org/10.1038/s41467-026-72183-4
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DOI: https://doi.org/10.1038/s41467-026-72183-4
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