Satellite observations have confirmed the largest bloom of macroalgae in the world, which has mostly formed in the last eight years, possibly as a result of human activities.
The mass of sargassum, a brown macroalgae, stretches 8,850km from West Africa to the Gulf of Mexico and weighs more than 20 million tons – heavier than 200 fully loaded aircraft carriers.
University of South Florida scientists used NASA satellite observations to track sargassum over the last 19 years. They found that since 2011, the mass has grown due to changes in higher flow of nutrients from the Amazon river, possibly caused by deforestation and human fertiliser use.
Dr Paula Bontempi, acting deputy director of NASA’s Earth Science Division, said: “The Great Atlantic Sargassum Belt suggests that we may be witnessing ecosystem shifts in our ocean that could have important implications for marine organisms and ecosystem services, which humans depend on.”
Before 2011, free floating sargassum in the ocean was mainly found in patches around the Gulf of Mexico and the Sargasso Sea on the western edge of the central Atlantic Ocean, but since then new blooms have contributed to create this record mass.
While sargassum patches in the open ocean contribute to ocean health, too much of it can block light and crowd out marine species, especially near the coast. The foul-smelling weed has also been washing up on beaches.
Chuanmin Hu of the USF College of Marine Science said: “The ocean’s chemistry must have changed in order for the blooms to get so out of hand.
“This is all ultimately related to climate change, as climate affects precipitation and ocean circulation.”
USF analysed data from NASA’s Moderate Resolution Imaging Spectroadiometer between 2000 and 2018. They had their findings published in Science.