Back in 2011, a large bulk of seaweed, measuring longer than the Brazilian coastline, appeared in the tropical Atlantic. The phenomenon left scientists worldwide confused, as the mentioned region generally lacks the elements needed to create such algae growth. But now, we might finally have some answers about the "Great Atlantic Sargassum Belt," as it's come to be called.
"There are probably multiple factors [contributing to seaweed growth]," explained Ajit Subramaniam, an oceanographer at Columbia University. "I would be surprised if there is one clear villain." So who do researchers suspect is (incidentally) working together to bring about the Great Atlantic Sargassum Belt? For starters, human and agricultural waste that's making its way from rivers to the ocean.
A recently published study in Nature Communications showed that the seaweed stretching from Brazil to the United States and the Caribbean has nitrogen levels 35% higher than thirty years earlier. The likely culprit? Runoff from urban areas and farms, as nitrogen is a common ingredient in fertilizers and often found in animal waste. But, as Ajit Subramaniam pointed out, other processes are enhancing the seaweed's growth.
Scientists told Reuters that the Great Atlantic Sargassum Belt is likely a result of climate change, destruction of the Amazon rainforest, and west-winding dust from the Sahara Desert in Africa, in addition to the human and agricultural waste runoff into the ocean. All of these factors are working together and continuing to build the now 9,000 kilometers-long seaweed band.
Rising temperatures worldwide have led to an increase in rainstorms, leading to more flooding and nitrogen runoff into our waters. The flooding of the Amazon River is probably one of the most significant contributors to seaweed growth, with currents then taking the organisms all around the coasts.
As for the Sahara Desert dust, researchers believe that the material is making its way west over the Atlantic, joining cloud formations, and coming down into the water as iron and phosphorus. "This phenomenon will continue until there is a change in public policy," commented Carlos Noriega, a scientist at the Federal University of Pernambuco in Brazil. "Treating sewage and stopping deforestation, that's the only way to control it," he added.