Beautiful blooming phytoplankton create swirling art in the Baltic Sea

This image released by NASA’s Earth Observatory shows a giant bloom created by phytoplankton off the Swedish coast

By Gege Li

Image
NASA Earth Observatory/ Joshua Stevens

MESMERISING swirls etch a fleeting pattern into the surface of the Baltic Sea that shifts with the currents. This colourful assembly, off the coast of south-east Sweden, is made up of high concentrations of phytoplankton. They are most likely to be cyanobacteria, which behave like plants and capture and store solar energy through photosynthesis.

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Such phytoplankton blooms are more common in the summer, when plenty of sunlight is available at the water’s surface. Blooms can span hundreds of square kilometres and last from a few days to several weeks, and no two are the same.

Phytoplankton fares particularly well in the Baltic Sea because the water contains plenty of phosphate, an essential nutrient for growth.

But blooms can signal trouble. If there are too many nutrients, often due to fertilisers or sewage leaking into water, phytoplankton can reproduce rapidly and the blooms explode in size. This can use up the water’s oxygen, producing “dead zones” where very few organisms can survive.

This image was taken on 15 August by the Operational Land Imager, a remote sensing instrument that takes images of wide areas of Earth’s landscape. It is onboard the Landsat 8 satellite that orbits Earth. NASA’s Earth Observatory released the image last week.