File:Bloom in the Black Sea (MODIS).jpg

English: The dark water of the Black Sea was tinted with swirls of light blue in late June 2023. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of the colorful scene on June 24.

The bright colors are the result of a widespread bloom of phytoplankton—microscopic plant-like organisms that float near the surface of the water year-round in relatively small numbers. When water temperature, sunlight length, and nutrient load are favorable, phytoplankton can reproduce explosively and create large floating colonies that can be seen from space.

The water of the Black Sea is enriched by nutrients carried in by the Danube, Dnieper, Dniester, Don and other rivers, creating fertile territory for the growth of phytoplankton. These microscopic algae, bacteria, and protists use chlorophyll to make their own food from sunlight and dissolved nutrients and are considered the “primary producers” of the seas and oceans. More than 150 different types of phytoplankton have been observed in the Black Sea over the years, and they support a rich bounty of fish and other marine organisms found here. On the other hand, an over abundance of these organisms can deplete oxygen dissolved in the water and cause stress to the other marine life that lives in the Black Sea.