16 Aug 2019 - High nutrient levels in 2018 resulted in a nearly 9,000-kilometer belt of Sargassum, a seaweed critical to many marine animals but also a nuisance when it washes up on shorelines, new results reveal.
Sargassum seaweed is an important source of food and shelter for many marine animals. But the algae can also be a nuisance when they wash up on coastlines: They can bury beaches, alter the coastal environment, and wreak havoc on tourism.
Nutrient-rich discharge from the Amazon River and the upwelling of cold, nutrient-laden water near West Africa are correlated with years of stronger algal blooms.
Scientists have now used satellite data to trace how a giant patch of Sargassum they’ve called the Great Atlantic Sargassum Belt grows and shrinks with changing environmental conditions. They suggest that higher levels of nutrient-rich discharge from the Amazon River and increased upwelling of cold, nutrient-laden water near West Africa are correlated with years of stronger algal blooms. These results are important for predicting Sargassum inundations, the researchers propose.
Spotting the Seaweed
Chuanmin Hu, an optical oceanographer at the University of South Florida in Tampa, and his team mined 19 years’ worth of Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations to pinpoint floating Sargassum.
Researchers analyzed the visible and near-infrared channels of the imagery to locate the distinctive yellow-brown seaweed in over 53,000,000 square kilometers of the Atlantic Ocean and the Intra-Americas Sea (which includes the Gulf of Mexico and the Caribbean). To do so, Hu and his colleagues looked for the distinctive red edge reflectance of photosynthesizing plants, which is caused by chlorophyll’s enhanced reflectance in the infrared. (Astronomers hope to use the same technique one day to spot plants on distant planets orbiting other stars.)
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