Using satellite observations, American scientists discovered an unprecedented algal bloom in the Great Atlantic Sargasso Belt.
The length and shape of the belt of marine brown algae, known as sargassum, depends on ocean currents and season. In some years, algae can spread from the west coast of Africa to the Gulf of Mexico. For example, it happened in 2018: their total mass, according to scientists, reached 20 million tons.
Scientists, led by the USF College of Marine Science, analyzed satellite data from 2000–2018 and saw that, from 2011, the weight of algae in the tropical Atlantic began to increase dramatically.
The team suggested that the belt is formed seasonally in response to two key “releases” of nutrients for algae. The first of these occurs in spring and summer, when fertilizer enters the ocean along with the waters of the Amazon. In recent years, the flow of nitrogen and phosphorus has increased as a result of massive deforestation and the emergence of new farmland.
The second “release” occurs in winter. This is a natural process called upwelling. The rise of deep ocean waters to the surface off the West African coast supplies algae with nutrients from the ocean floor.
Since 2011, sargassum began to appear in those parts of the Atlantic Ocean, where it was not previously observed. He captured the coastlines, creating problems for tourism and fishing.
Last year, Barbados even declared a state of emergency because of kelp.
“The scale of this bloom is really huge,” said Woody Turner, manager of the Environmental Prediction Program at NASA headquarters in Washington.
In moderate doses, sargassum is good for the ocean. It provides habitat for turtles, crabs, fish and birds, and also releases oxygen through photosynthesis, like other plants.
But the abundance of brown algae, on the contrary, prevents some marine species from moving and breathing. Dying off and sinking to the bottom, sargassum damages or destroys coral and seagrass. On the beaches of Sargassum, gaseous hydrogen sulfide is released and it smells like rotten eggs.