NASA satellites have seen thousands of miles of brown seaweed that extends across the Atlantic Ocean.
Recent observations from the satellites reveal that the Atlantic Ocean now hosts a carpet of brown algae that extends some 5,500 miles (8,850 km) from the coast of West Africa to the Gulf of Mexico. It is the largest algae bloom in the world.
Officially called the Great Atlantic Belt Sargassum, flowering is responsible for the masses of algae that have plagued beaches throughout the Caribbean and the Gulf of Mexico for years.
Scientists have been working to discover why algae have gotten out of control, and a study published in the journal Science last week suggests that deforestation and the use of fertilizers may be to blame.
Sargassum has "gotten out of hand"
Sargassum is a benign brown algae that produces oxygen and provides habitat for crabs, fish and birds. It floats in patches in the Gulf of Mexico and in the Sargasso Sea (which gets its name from the algae).
But in 2011 something changed, according to the recent study of the University of South Florida. The populations of Sargassum grew, and every year since then (with the exception of 2013) large blooms of brown algae have been seen. Last year was particularly bad, with more than 20 million tons of Sargassum covering the Atlantic. The algae formed huge groups along the coasts of the Caribbean, the Gulf of Mexico and the east coast of Florida.
"The chemistry of the ocean must have changed for the flowers to get out of hand," said Dr. Chuanmin Hu, the study's principal investigator, in a press release. Hu has studied Sargassum using satellites since 2006.
To study seaweed, the researchers collected images of the NASA MODIS satellite taken between 2000 and 2018 in the Atlantic Ocean, the Caribbean and the Gulf of Mexico. The computers analyzed each pixel that contained Sargassum in the images to determine the density of the marine algae. The results suggested that the summer biomass of Sargassum has increased by approximately 800% since the first important flowering in 2011.
And the flowering keeps growing.
In small quantities, Sargassum is part of a healthy ocean ecosystem. But when the algae form a mat on the surface of the water, they can restrict the movement patterns of the marine animals and even make it difficult for them to breathe. The dead Sargassum also sinks and chokes the corals.
In addition, Sargassum stinks. As marine algae rot, they release hydrogen sulfide gas that has a characteristic rotten egg odor. Barbados declared a national emergency due to the amount and stench of decaying algae in June 2018. This year is no better, with Sargassum stinking beaches and striking a blow to tourism in Mexico and Florida.
Less forest and more fertilizer.
According to a recent study, increases in deforestation and the use of fertilizers along the Amazon River since 2010 are a likely cause of the increase in Sargassum.
Flowering is seasonally formed since it feeds from two sources of nutrients. The first is made by man: in the spring and summer, runoff flows into the Amazon River, which carries nutrients such as nitrogen and phosphorus due to deforestation and fertilizers. That river water then enters the ocean. The second source of seaweed feed is natural: in the winter, seawater rises from the depths of the West African coast, bringing nutrients to the surface.
The researchers behind the recent study analyzed fertilizer consumption in Brazil, deforestation rates in the Amazon and measurements of nitrogen and phosphorus taken in the Atlantic Ocean. Their analysis revealed that between 2011 and 2018, fertilizer consumption in Brazil increased by about 67% compared to rates in 2002. The total loss of forests in the Brazilian Amazon increased by 25%.
Read more: Old photos from the EPA reveal what the waterways in the United States looked like before pollution was regulated
All that extra nitrogen and phosphorus acts as fuel for Sargassum algae. The researchers said that a double blow from a combination of manmade and naturally occurring sources probably caused the first flowering in 2011. Ocean currents drove Sargassum from its natural waters until it became a huge brown blanket from West Africa to Mexico .
"Based on the last 20 years of data, I can say that the belt is very likely to be a new normal," Hu said in the statement.
The proliferation of algae requires further study.
Because the flowering of Sargassum threatens tourism, sanitation of beaches, marine life and fisheries, the study authors suggested that more research should be done to learn about the flowering behavior of Sargassum and determine how to address the problem.
"The evidence for nutrient enrichment is preliminary and is based 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 Great Belt of the Atlantic Sargassum. Hu believes that that is not the main cause, but he sees a connection.
"Ultimately, all this is related to climate change because it affects rainfall, ocean circulation and even human activities, but what we have shown is that these blooms do not occur due to the increase in water temperature," he said. Hu "They are probably here to stay."