Interannual variability in Sargassum seaweed transport from the Sargasso Sea to the equatorial Atlantic and Caribbean Sea

Since 2011, Caribbean beaches have been regularly swamped by large quantities of a floating seaweed called Sargassum. Blooms of Sargasssum form large mats in the equatorial Atlantic and at their peak can span from the Gulf of Mexico to west coast of Africa, forming the Great Atlantic Sargassum Belt (GASB). Sargassum beaching events have significant environmental and socio-economic impacts, including impacts on fisheries, tourism, nesting marine animals, and coral reefs. Prior to 2011, Sargassum was predominantly found entrained within the currents of the North Atlantic Subtropical Gyre in the Sargasso Sea. It is thought that an extreme negative phase of the North Atlantic Oscillation (NAO) in 2010/2011 may have produced conditions in the Sargasso Sea that allowed Sargassum to escape and populate further south. The NAO impacts the strength and direction of winds over the Atlantic and modulates ocean properties such as sea surface temperature (SST) and mixed layer depth. Could a change in wind and ocean circulation in 2010 and 2011 explain how Sargassum escaped the ocean gyre as an extreme one-off event? In this study, Lagrangian particle tracking simulations are used to investigate the likelihood of Sargassum leaving the Sargasso Sea between 2009 and 2021, using a velocity field from the Copernicus Marine Environment Monitoring Service (CMEMS) GLORYS12V1 reanalysis. The study’s results show interannual variability in the escape of particles eastwards from the Sargasso Sea into the equatorial Atlantic and Caribbean Sea.