Scientists at the Max Planck Institute for Chemistry found that deep-water phosphorus carried upward by equatorial upwelling, combined with nitrogen supplied by cyanobacteria living on Sargassum, is what drives the massive blooms sweeping the Atlantic. Coral cores show this nutrient engine has strengthened since 2011, aligning with surges in Sargassum growth and ruling out older explanations like Saharan dust or river runoff.