Satellite weeds out nautical nemesis

Sargassum seaweed, famous in nautical folklore for entangling ships in its dense floating vegetation, has been detected from space for the first time thanks to an instrument aboard the European Space Agency’s environmental satellite, Envisat.

Sargassum seaweed has been detected from space for the first time.

Researchers hope the ability to monitor Sargassum globally will allow them to understand better the carbon cycle of the ocean and better predict climate change.

Using optical radiance data from the Medium Resolution Imaging Spectrometer (MERIS) aboard Envisat, Dr Jim Gower and Stephanie King of the Canadian Institute of Ocean Sciences and Dr Chuamin Hu of the US University of South Florida were able to identify extensive lines of floating Sargassum in the western Gulf of Mexico.

“This appears to be the first report of a satellite image of Sargassum,” Dr Gower said. “It is usually associated with the area of the North Atlantic known as the Sargasso Sea after the Sargassum encountered there by early explorers. Our observations of Sargassum lines extending over large areas of the Gulf show that in this area and season it represents a significant fraction of marine primary productivity.”

Marine primary production is the process by which floating vegetation, such as phytoplankton and seaweed, absorb atmospheric carbon dioxide through photosynthesis and convert it into organic carbon. By absorbing half of the carbon dioxide emitted into the atmosphere, the oceans have a profound influence on climate, making them major areas of interest for climate modellers.

The imaging was based on the amount of chlorophyll present in the seaweed. MERIS is uniquely suited for this as it can measure light emittance at 665, 681 and 709nm – exactly the fluorescence emission from chlorophyll a.

Dr Gower said: “This has allowed us to find so many interesting things, including Sargassum and Antarctic super blooms. It really gives us a new and unique view of the Earth.”