Sentinel-3 spots Sargassum seaweed

By Ben Loveday (PML) and Hayley Evers-King (EUMETSAT)

Sargassum seaweed occurs naturally in its namesake — the Sargasso Sea. However, recent studies using time series of satellite data (Wang et al., 2019) have found an increase in both spatial extent and density of this seaweed — stretching across the Atlantic Ocean.

Sargassum plays an important role in ocean ecosystems as a habitat for pelagic (open ocean) animals, including various species of fish and turtles.

However, when large amounts of this seaweed reach the shore, they can cause numerous problems for both people and animals. Beaches full of rotting seaweed can affect tourism, and pose a potential health issue for beachgoers (Figure 1).

Satellite ocean colour data provides images at suitable temporal and spatial scales to track Sargassum from the open ocean, to the coastal zone. Figures 2 and 3 show how Sargassum can be detected using ocean colour data from the OLCI sensor aboard Sentinel-3, in both true colour imager (Figure 2) and using specific mathematical formulae (‘algorithms’) such as those used in the aforementioned study (Figure 3).

In a project by CLS, funded by the European Space Agency, satellite data from various sensors including OLCI is being used to track the Sargassum and help local managers prepare for its impacts.

Additional content

The great Atlantic Sargassum belt, Wang et al., 2019
A novel ocean color index to detect floating algae in the global oceans, Chuanmin Hu, 2009
Sargassum: The biggest seaweed bloom in the world (BBC News)