File:Blooms in the Black Sea (MODIS 2020-06-07).jpg

English: Jewel-toned swirls filled the Black Sea and Sea of Azov in early June 2020. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of the scene on June 5.

The milky-blue swirls that grace the Black Sea are most likely caused by blooms of phytoplankton—microscopic plant-like organisms that live in these waters year-round in small numbers. When conditions are ideal—adequate light, nutrients, and water temperature—phytoplankton can reproduce explosively, creating large blooms that are easily seen from space.

More than 150 different types of phytoplankton have been observed in the Black Sea. They form the base of the marine food web, supporting a rich bounty of fish and other marine life. One type of phytoplankton found in the Black Sea are coccolithophores—microscopic plankton that are plated with white calcium carbonate. As coccolithophore blooms often appear milky blue from space, it is likely that these are present in large numbers in the Black Sea.

The Sea of Azov, which is the smaller body of water located just north of the Black Sea in this image, sports swirls of green and tan. This color is likely primarily the result of sediment carried in from the Don and Kuban River but the color also may be caused at least in part by phytoplankton.