What Is Actually Causing the Sargassum Explosion?

What is actually causing the Sargassum explosion? Ask around and you’ll often hear the same answer: Climate change. Warmer oceans. More Sargassum. But the science is telling a much more interesting story. A recent 2026 study looking at more than 30 years of data from the Sargasso Sea found something that might surprise you: As the ocean became warmer, Sargassum biomass actually declined. So if warming alone isn’t driving the massive blooms, what is? Increasingly, the evidence points toward a combination of nutrients and ocean dynamics. • Changes in circulation helped move Sargassum into the tropical Atlantic • Phosphorus and nitrogen provide the nutrients needed for rapid growth • River and land-based nutrient inputs may contribute to this nutrient supply • Dense Sargassum mats can recycle nutrients within their own ecosystem • Currents, winds and upwelling influence where those nutrients, and the Sargassum, end up The result is the Great Atlantic Sargassum Belt, stretching thousands of kilometers across the Atlantic and producing extraordinary amounts of biomass. Climate change may influence many of these processes. But “warmer water = more Sargassum” simply doesn’t explain what we’re seeing. Understanding what actually drives these blooms matters. Sargassum is increasingly looking like a long-term challenge for the Atlantic and Caribbean. Which leaves coastal regions with one urgent question: What do we do with all that biomass?