Satellites have spotted the biggest seaweed bloom in the world

James Marshall
July 7, 2019

The belt of brown macroalgae called Sargassum forms its shape in response to ocean currents. 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 nearly 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.

Scientists have measured what they say is the largest seaweed bloom on record, stretching 8,850 kilometres (nearly 5,500 miles) across the Atlantic Ocean and made up of some 20 million metric tons of Sargassum algae - more than the weight of 200 fully loaded aircraft carriers.

Scientists used field study observations and environmental data to provide context for their satellite survey, determining that the belt of seaweed blooms seasonally and responds to two main nutrient inputs.

The prospect, the team says, could be strengthened by the finding that increasing levels of nutrients are being flushed into the ocean via the Amazon in the spring and summer each year, as a result of human activities including deforestation and fertiliser use.

In the winter, upwelling off the West African coast delivers nutrients from deep waters to the ocean surface where the Sargassum grows.

"The oceans are connected across the regions and we are going to see more sargassum coming to the Florida coast", Wang said. "It is reasonable to suggest that the 2011 massive bloom is therefore the result of nutrient accumulations since 2009, resulting from stronger upwelling in the eastern Atlantic and excessive Amazon River discharges in the western Atlantic".

There have been ever-increasing amounts of the seaweed in the ocean every summer since 2011, with the biggest ever bloom detected previous year, according to a paper in Science this week. Barbados went so far as to declare a national emergency when troves of the microalgae threatened its valuable tourism industry.

To unravel the mystery, the team analyzed fertilizer consumption patterns in Brazil, Amazon deforestation rates, Amazon River discharge, two years of nitrogen and phosphorus measurements taken from the central western parts of the Atlantic Ocean, among other ocean properties. Researchers believe increases in deforestation and fertilizer use could be factors fueling blooms. In a related Perspective, James Gower and Stephanie King highlight the way satellite sensors are especially well-suited to monitor Sargassum blooms. "They are probably here to stay", he said. Since then, there have been major blooms nearly every year, and there's no sign of that trend changing - the latest spread stretched all the way from West Africa to the Gulf of Mexico.

Looking ahead, the researchers would like to develop a model to predict the growth of blooms in the future. Largely due to a lack of large-scale Sargassum data, little is known about the cause of these Sargassum expansions, particularly the role of atmospheric, oceanic and/or climatic conditions in driving them. "We need a lot more follow-on work". Then please consider donating today to ensure that Eurasia Review can continue to be able to provide similar content.

Other reports by Click Lancashire

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