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article imagePlanet's largest seaweed bloom just keeps getting bigger

By Karen Graham     Jul 5, 2019 in Environment
It weighs 20 million tons, stretches from western Africa to the Gulf of Mexico, and washes up on beaches creating a malodorous stench. Now scientists say a vast swathe of brown seaweed could be becoming an annual occurrence.
Sargassum, a brown seaweed usually seen in the Caribbean and southern Florida region of the Gulf of Mexico comes from a region in the North Atlantic Ocean bounded by four currents forming an ocean gyre, This is where the Sargasso Sea can be found.
However, since around 2011, the brown seaweed that usually blooms in the North Atlantic has started blooming across a stretch of open ocean between Africa and South America - an unusual place for a massive seaweed bloom. The blooms have grown yearly since then, repeatedly sweeping across Atlantic and Caribbean beaches, trapping nesting sea turtles and disrupting local tourism industries.
The Great Atlantic Sargassum Belt
It didn't take too long before scientists figured out what was going on and their results were published July 5 in the journal Science. The new research shows the seaweed bloom has appeared almost every year since then, forming the largest bloom of macroalgae ever recorded, and it seems to be getting bigger. The belt of seaweed stretches for around 5,500 miles (8,850 kilometers) from the coast of West Africa to the Gulf of Mexico,
"We analyzed almost 20 years of satellite records," Mengqiu Wang, a postdoctoral researcher at the University of South Florida and co-author on the study, told Live Science. This allowed the researchers to analyze any long-term environmental change and year-to-year variations in growth.
Copernicus Sentinel-2 image of mouth of the Amazon River running into the Atlantic Ocean. Note the b...
Copernicus Sentinel-2 image of mouth of the Amazon River running into the Atlantic Ocean. Note the brown, muddy water, runoff from deforestation. Earth observation satellites have been instrumental in highlighting the vulnerability of the rainforests by documenting the scale of deforestation.
European Space Agency (CC BY-SA 3.0 IGO)
The research team identified a tipping point in 2009. There was an unusually large discharge from the mouth of the Amazon River into the Atlantic, caused by excessive deforestation. Added to this event was an upwelling of nutrient-rich water off the west coast of Africa in the winter of 2010.
The upwelling of nutrient-rich deep sea waters further enriched the surface waters, allowing sargassum to thrive in the summer of 2011. This same combination of the two events led to especially large blooms in 2014, 2015 and 2017. But in 2018, the largest seaweed bloom ever recorded took place. The Great Atlantic Sargassum Belt grew to a mass of more than 20 million metric tons.
The good, the bad and the stinky impacts
Sargassum is made up of berry-like structures - gas-filled bladders known as pneumatocysts - which provide buoyancy to the plant and allows it to float on the ocean's surface. It provides a habitat for fish, turtles and even birds, and that is a good thing.
Nasa’s satellite data confirms that the record-breaking seaweed belt forms in the summer months  w...
Nasa’s satellite data confirms that the record-breaking seaweed belt forms in the summer months, with 2015 and 2018 having the biggest blooms. Photograph: USF College of Marine Science
NASA satellite data
"As sargassum decays it consumes the oxygen, creating low oxygen conditions, which is not a good condition for marine life in a coastal ecosystem," Wang said. "Coral reefs and seagrass ecosystems can suffer when high levels of sargassum change the water chemistry and block organisms from moving freely.
The amount of sargassum ending up in piles on beaches in Mexico, the Caribbean, and Florida beaches is astounding. Barbados declared a state of emergency in 2018, according to a government statement, as sargassum piled onto the beaches the island nation, reports The Guardian.
So far 2019 also looks set for a huge bloom. “It’s another record year,” said Dr. Chuanmin Hu, co-author of the study from the University of South Florida. He added that the frequent recurrence of the Great Atlantic Sargassum Belt raises the possibility that this may be the new status quo. “We cannot predict individual years, but we can predict the next decade in general,” he said.
More about sargassum, algae belt, west africa to Gulf of Mexico, deforestation of Amazon, excess nutrients
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