ESA’s Sentinel-2A satellite has captured detailed images of a phytoplankton bloom in the middle of the Baltic Sea on 7 August 2015. This particular bloom contains cyanobacteria – an ancient type of marine bacteria that, like other phytoplankton, capture and store solar energy through photosynthesis.
This Sentinel-2A image shows an eye of algal bloom in exquisite detail as well as a ship. The ship’s wake can be seen as a straight dark line where the bloom has been disturbed by the ship’s propellers. The image has a spatial resolution of 33 feet (10 m). Image credit: Copernicus Sentinel data / ESA.
The Baltic Sea faces many serious challenges, including toxic pollutants, deep-water oxygen deficiencies, and blooms of cyanobacteria affecting the ecosystem, aquaculture and tourism.
The situation was so bad that in 1974 the Helsinki Convention for the Protection of the Marine Environment of the Baltic Sea Area was created to improve the state of the sea.
“Major cyanobacteria blooms like this one appear in the Baltic Sea nearly every summer, and they always look like this in the satellite data,” explained Dr Norman Kuring, an oceanographer at NASA’s Goddard Space Flight Center.
Blooms in the Baltic Sea usually appear as a green-yellow soup or a mass of blue-green threads along density gradients within the sea.
The streaks and filaments, eddies and whirls of biological activity are clearly visible in these new images taken with Sentinel-2A’s Multi Spectral Instrument.
This composite image from Sentinel-2A taken on 7 August 2015 has a spatial resolution of 33 feet (10 m). It shows an algal bloom in the central Baltic Sea. The algae is concentrated in locations where the vertical and horizontal water movements in the Baltic Sea generate the best nutrient and light conditions for algal growth, which are then drawn out by the water circulation. Image credit: Copernicus Sentinel data / ESA.
Cyanobacteria have qualities similar to algae and thrive on phosphorus in the water. High water temperature and sunny, calm weather often lead to particularly large blooms that pose problems to the ecosystem and, therefore, aquaculture and tourism.
Toxicity varies between different species, but can also vary within the same species. Because of this, several teams monitor the status of blooms in the region using ships. However, satellites can provide a synoptic view that ships alone cannot.
“Sentinel-2A multispectral imager data of biological activity are delivered at a much higher spatial resolution than current operational numerical ocean prediction systems. This provides unique and complementary information to monitor the development of potentially harmful blooms,” said Dr Craig Donlon, an ocean scientist with ESA.
“To support safe aquaculture and tourism we need to have better knowledge of the ecosystem and physical dynamics in the upper ocean, which is expressed in the horizontal structures we can see in the Sentinel-2A imagery.”
“For example, the linear features in the algal bloom signature across the image suggest that internal waves are present. As these waves propagate and break, they energize the upper layers of the water column mixing typically deeper oxygen-depleted waters and change the distribution of the bloom.”
