Algal bloom in the Baltic Sea
An algal bloom is a rapid increase or accumulation in the population of algae (typically microscopic) in a water system. Cyanobacteria blooms are often called blue-green algae. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognised by discoloration of the water resulting from the high density of pigmented cells.
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In most of the Baltic Sea, there are two annual blooms, the spring bloom and the cyanobacterial (also called blue-green algae) bloom in late summer. In the southern Baltic Sea, autumnal blooms are regular, too. Additionally, exceptional blooms formed by various species can occur locally.
When large quantities of microscopic, free-floating algae (phytoplankton) perform photosynthesis, multiply and lump together we see them as a greenish, yellowish, brownish or reddish layer on the sea surface or as a thick 'soup' in the water. These visible accumulations (or aggregations) of algae are usually referred to as algal blooms.
The term algal bloom is used for events when phytoplankton multiply rapidly during a limited time period due to the rich supply of plant-available nutrients in the water. Algal blooms are a normal and essential part of life in the sea, but they become a problem when they occur too often, are too large, last for too long a time, and/or produce toxic substances.
Blue-green algal blooms, which are basically a population explosion of these organisms as a result of increased nutrients in seawater, cover the Baltic. The highest concentrations occur in the Central Baltic and around the island of Gotland. The Bay of Riga is also the site of algal blooms. The blooms are less intense in the Gulf of Finland and in the Archipelago Sea to the east. Near the coast of Finland, surface wind has cleared the waters of algae accumulations. Some species of blue-green algae are toxic to humans and the surveillance of blooms on the surface and in the underlying water masses is an important task to preserve the health and safety of people living along the coasts. Blue-green algae are not really algae at all but a bacteria known as "cyanobacteria".
Intensive blooms like the one observed by Envisat in this related article were a rare phenomenon a hundred years ago, but have become increasingly frequent in recent years as a result of the increase in temperature in Baltic and Finnish coastal waters, as well as the increase of pollution in these seas which provide ample nutrients for these organisms.
Today our aim is to show the large phenomenon of Algal Bloom which occurred during August in the Baltic Sea. The summer heat promotes the proliferation of cyanobacteria, and the phenomenon is clearly a problem for the ecosystem, tourism and aquaculture. In these Landsat 8 images, acquired on 9 and 18 August 2015, we can see not only an extraordinary algal bloom, but also the whole dynamic biological activity, with filaments and stripes, swirls and eddies.
In fact, these images acquired by Landsat 8 show a massive algal bloom glowing green in the water, and it is even possible to see of ships through it. These vessels are visible by the black trail they leave behind (as seen in the full images).
Another aim of these images is to promote the opportunity to download Landsat data through the ESA portals, where images captured every day are made available in near real time to the users and the scientific community.
Landsat full resolution data products are freely available for immediate download at: