They confirmed that the belt of brown macroalgae called Sargassum forms its shape in response to ocean currents, based on numerical simulations.
A team of scientists from the University of South Florida, Florida Atlantic University, and Georgia Institute of Technology used NASA satellite observations to discover the largest bloom of macroalgae in the world, an event that blankets the surface of the tropical Atlantic Ocean from the west coast of Africa to the Gulf of Mexico. As recorded on June 8, 2018, the Great Atlantic Sargassum Belt spanned 5,550 miles and was made up of more than 20 million tonnes of biomass.
The proof for nutrient enrichment is preliminary and based mostly on restricted field data and different environmental information, and we'd like further analysis to substantiate this hypothesis, mentioned Dr. Chuanmin Hu of the USF College of Marine Science, who led the study. "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". The Sargassum has bloomed every year since 2011, with the exception of 2013.
Monthly mean Sargassum density for the month of July from 2011 to 2018.
They also theorize another big concern could be at play - a change in the ocean's chemistry.
Copernicus Sentinel-2 image of mouth of the Amazon River running into the Atlantic Ocean.
To bolster their case, the authors analysed fertiliser consumption patterns in Brazil, along with deforestation rates in the Amazon - both of which matched nicely with the Sargassum growth trend beginning around nine years ago. The blooms have grown yearly since then, repeatedly sweeping across Atlantic and Caribbean beaches, trapping nesting sea turtles and disrupting local tourism industries.
Using satellite data from NASA as well as samples collected in the field, the researchers have identified a tipping point that happened back in 2011.
Dr. Hu said, "This is all ultimately related to climate change because it affects precipitation and ocean circulation and even human activities, but what we've shown is that these blooms do not occur because of increased water temperature".
"They are probably here to stay".
In general, predicting future blooms is difficult, Hu said, because the blooms depend on a wide-ranging spectrum of factors that are hard to predict. However, the amount and spatial extent of Sargassum has increased substantially over the last decade; entire flotillas of wayward seaweed mats have increasingly begun to wash ashore, inundating Atlantic and Caribbean beaches and resulting in significant environmental and economic problems. 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. "It's another record year", said Hu, adding that the frequent recurrence of the Great Atlantic Sargassum Belt raises the possibility that the phenomenon may be the new status quo.
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