Swirls of cyanobacteria in the Baltic Sea

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Blooms of blue-green algae were visible across the Baltic Sea in Sentinel-3 imagery during August 2019.

Date & Time
9 August 2019 09:25 UTC
Level 1 Ocean Colour data

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

Cyanobacteria are found in environments around the world, and are one of the oldest groups of species on Earth.

They photosynthesize, absorbing carbon dioxide and producing oxygen, and are thought to be the modern day progeny of the ancestors of all plants, and much of life itself. Ancient cyanobacterial species changed the face of our planet during the Great Oxygenation Event, which caused mass extinction of early anaerobic lifeforms, and paved the way for all life that depends on the current atmospheric composition.

They are troublemakers in both historical and modern contexts, with blooms of cyanobacteria in coastal and fresh waters being linked to various health impacts in humans.

They can proliferate widely, particularly during summer periods where warm temperatures and calm weather lead to calm seas. They are small, and sometimes contain gas bubbles within their structure to help them float on the surface of the waters they inhabit. These combined factors make blooms of cyanobacteria very clear to view from space in certain regions.

In Figure 1, the OLCI instrument on the Sentinel-3A satellite captured these blooms being swirled by light currents in the Baltic Sea after the European heatwave in the summer of 2019.

Figure 1
Figure 1: A Red-Green-Blue composite made using measurements of light at wavebands specific to the OLCI sensor, showing green cyanobacteria blooms in the middle of the Baltic sea on 9 August, 09:25 UTC.
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