Sentinel-3 spots Sargassum seaweed. Credit: Guajillo studio

Sentinel-3 spots Sargassum seaweed

3 July 2019 14:00 UTC

Photo credit: Guajillo studio

Sentinel-3 spots Sargassum seaweed. Credit: Guajillo studio
Sentinel-3 spots Sargassum seaweed. Credit: Guajillo studio

In early July 2019, Sentinel-3 captured images showing blooms of Sargassum seaweed, which made the headlines due to their rapid growth and how far they spread.

Last Updated

04 October 2023

Published on

03 July 2019

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).

 Sargassum rotting on a beach. Credit: Guajillo studio
Figure 1: Sargassum rotting on a beach. Credit: Guajillo studio

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).

 An enhanced colour (Red-Green-Blue) Rayleigh corrected OLCI RGB image, showing Sargassum accumulations (green string-like features) near Tobago and Grenada, 3 July 14:00 UTC.
Figure 2: An enhanced colour (Red-Green-Blue) Rayleigh corrected OLCI RGB image, showing Sargassum accumulations (green string-like features) near Tobago and Grenada, 3 July 14:00 UTC
 Sargassum can be identified from ocean colour data using the Floating Algal Index algorithm of Chuanmin Hu.
Figure 3: Sargassum can be identified from ocean colour data using the Floating Algal Index algorithm of Chuanmin Hu
 

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)

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