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NASA satellites have spotted thousands of kilometers of brown algae extending over the Atlantic Ocean.
The latest satellite observations reveal that the Atlantic Ocean is now home to a carpet of brown seaweed that stretches 8,850 kilometers from the coast of West Africa to the Gulf of Mexico. large proliferation of algae in the world.
Officially called the Great Sargassum Atlantic Belt, blooming is responsible for the masses of algae that have raged for years on the beaches of the Caribbean and the Gulf of Mexico.
Scientists are struggling to understand why the algae have become so unmanageable. A study published in the journal Science last week suggests that deforestation and fertilizer use may be to blame.
Sargassum became 'uncontrollable'
Sargassum is a benign brown algae that produces oxygen and is a habitat for crabs, fish and birds. It floats in patches in the Gulf of Mexico and the Sargasso Sea (which takes its name from the seaweed).
But in 2011, something changed, according to the recent study from the University of South Florida. Populations of Sargassum have exploded and, every year since (with the exception of 2013), brown algae have flourished. Last year was particularly bad, with more than 20 million tonnes of Sargassum covering the Atlantic. The algae formed enormous masses along the shores of the Caribbean, the Gulf of Mexico and the east coast of Florida.
"The chemistry of the ocean must have changed so that the proliferation is so uncontrollable," said Dr. Chuanmin Hu, senior research scientist, in a press release. Hu has been studying Sargassum with the help of satellites since 2006.
To study algae, researchers collected images of NASA's MODIS satellite, taken between 2000 and 2018, in the Atlantic Ocean, the Caribbean, and the Gulf of Mexico. The computers analyzed each pixel containing sargasses in the images to determine the density of the algae. The results suggest that the summer biomass of Sargassum has increased by about 800% since the first major bloom in 2011.
And the bloom is still growing.
In small quantities, Sargassum is part of a healthy ocean ecosystem. But when the alga forms a carpet on the surface of the water, it can limit the movement habits of marine animals and even make breathing difficult. Dead Sargassum sinks and chokes the corals.
In addition, Sargassum stinks. When the algae on the beach rot, they release hydrogen sulphide with a distinct smell of rotten eggs. Barbados declared a national emergency because of the amount and stink of decaying algae in June 2018. This year is no better, with Sargassum drawing its beaches and carrying a major blow to tourism in Mexico and Florida.
Less forest and more fertilizer
According to a recent study, the increase in deforestation and fertilizer use along the Amazon River since 2010 is a likely cause of the Sargassum outbreak.
Flowering is seasonal, as it feeds on two sources of nutrients. The first is of human origin: in spring and summer, runoff flows into the Amazon River, carrying nutrients such as nitrogen and phosphorus resulting from deforestation and fertilizers. This river water then enters the ocean. The second source of algae-based foods is natural: in winter, seawater rises from the depths of the West African coast, carrying nutrients to the surface.
The researchers behind the recent study examined fertilizer consumption in Brazil, Amazon deforestation rates, and nitrogen and phosphorus measurements taken in the United States. ;Atlantic Ocean. Their analysis revealed that between 2011 and 2018, fertilizer consumption in Brazil had increased by about 67% compared to the 2002 rates. The total loss of forests in the Brazilian Amazon increased by 25%. %.
Read more: EPA-era photos reveal what American water courses looked like before pollution was regulated
All this supplement of nitrogen and phosphorus serves as fuel for Sargassum algae. The researchers said that one out of two shots from a combination of anthropogenic and natural sources probably caused the first bloom in 2011. The ocean currents carried Sargassum off its natural waters until It becomes a huge brown blanket going from West Africa to Mexico. .
"Based on the data of the past 20 years, I can say that the belt will most likely be a new normal," Hu said in a statement.
Algal blooms require further study
As the proliferation of Sargassum threatened tourism, beach clean-up, marine life and fisheries, the study authors suggested further research to better understand the behavior of Sargassum proliferation and how to solve the problem. .
"Evidence of nutrient enrichment is preliminary and relies on limited field data and other environmental data, and we need more research to confirm this hypothesis," Hu said.
Other research has also suggested that climate change and warming ocean temperatures have played a role in the formation of the Greater Sargassum belt of the Atlantic. Hu thinks that's not the main cause, but sees a connection.
"All of this is ultimately linked to climate change because it affects rainfall, ocean circulation and even human activities, but we have shown that these blooms do not occur because of rising water temperatures," Hu said. "They are probably here to stay."
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