Link to paper https://www.nature.com/articles/s43247-025-02074-x

Scientists in Florida believe they have identified a “tipping point” in atmospheric conditions in the Atlantic Ocean they say caused giant clumps of toxic seaweed to inundate beaches around the Caribbean in recent summers.

Previous theories for the Great Atlantic Sargassum Belt that has killed marine animals, harmed human health and plagued the tourism industry in several countries include a surfeit of nutrients in the water, such as nitrogen and phosphorus in runoff from intensive farming and carried into the ocean in the Congo, Amazon and Mississippi rivers.

While marine scientists at the University of South Florida (USF) acknowledge that as a contributory factor, they say the primary source of nutrients is a seasonal phenomenon known as vertical mixing in which shifting winds churn up the ocean and deepwater nutrient concentrations are brought to the surface.

They identified atmospheric pressure changes over the Atlantic beginning around 2009 as the tipping point, with variations in circulation and wind patterns pushing more sargassum into the warmer waters of the tropics, where it grew through photosynthesis into the massive blooms that eventually ended up on the beaches of the Caribbean and the US Gulf coast.