EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Post-2011 variability of the great Atlantic Sargassum belt attributed to changing winds and currents

Robert Marsh1, Nikolaos Skliris1, Hazel Oxenford2, and Kwazi Appeaning Addo3
Robert Marsh et al.
  • 1University of Southampton, National Oceanography Centre, Southampton, School of Ocean and Earth Science, Southampton, United Kingdom of Great Britain – England, Scotland, Wales (
  • 2Centre for Resource Management and Environmental Studies (CERMES), University of the West Indies, Cave Hill, Barbados
  • 3Department of Marine and Fisheries Sciences, College of Basic and Applied Sciences, University of Ghana, Accra, Ghana

Since 2011, Sargassum seaweed has proliferated across the tropical North Atlantic, evident in Floating Algae Index (FAI) images for the Central Atlantic region (38-63°W, 0-22°N) over 2000-2020. To investigate the role of physical drivers in post-2011 Sargassum blooms, conditions are examined across the wider tropical Atlantic. Of particular consequence for the growth and drift of Sargassum are patterns and seasonality of winds and currents. In years when the FAI index is high (2015, 2018), the Intertropical Convergence Zone (where Sargassum accumulates) was displaced southward, towards nutrient-rich waters of the Amazon river plume and the equatorial upwelling zone. Strong enhancement of the North Brazil Current retroflection and North Equatorial Counter Current circulation system in 2015 and 2018 may have increased nutrient availability/uptake for Sargassum in the North Equatorial Recirculation Region. To first order, these changes are associated with modes of natural variability in the tropical Atlantic, notably a negative phase of the Atlantic Meridional Mode in 2015 and 2018, and a positive phase of the Atlantic Niño in 2018. The influence of anomalous winds and currents on Sargassum drift during years of high and low FAI are explored with virtual particle tracking, using surface currents from an eddy-resolving ocean model hindcast and optional % windage, to quantify the variable partitioning between Sargassum that is westward-bound to the Caribbean and eastward-bound to west Africa.

How to cite: Marsh, R., Skliris, N., Oxenford, H., and Appeaning Addo, K.: Post-2011 variability of the great Atlantic Sargassum belt attributed to changing winds and currents, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12381,, 2021.

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