Phytoplankton blooms in the Baltic Sea

These natural-color images, acquired on August 15, 2020, with the Operational Land Imager (OLI) on Landsat 8, show a late-summer phytoplankton bloom swirling in the Baltic Sea. The images feature part of a bloom located between Öland and Gotland, two islands off the coast of southeast Sweden. Note the dark, straight lines crossing the detailed image: these are the wakes of ships cutting through the bloom.

Confirmation of the type of phytoplankton within this bloom would require the analysis of water samples. But experts familiar with blooms in this region say it is likely to be cyanobacteria—an ancient type of marine bacteria that captures and stores solar energy through photosynthesis. Large, late-summer blooms of cyanobacteria occur almost every year in the Baltic Sea.

Sediment cores extracted from the seafloor indicate that blooms of cyanobacteria have occurred in the Baltic Sea for thousands of years and they have played an important role in this aquatic ecosystem. Cyanobacteria are “nitrogen fixers” that can convert molecular nitrogen into ammonia—a more biologically useful form of nitrogen that all phytoplankton can use as a nutrient to fuel growth. Cyanobacteria do especially well in the Baltic Sea, where there is ample phosphate—another nutrient important for the organism to grow.   NASA