This picture, taken on 29 May 2017 by NASA’s Aqua satellite, shows vibrant turquoise phytoplankton blooms swirling in the Black Sea.
Phytoplankton are the microscopic photosynthesing organisms at the foundation of the oceanic food web, providing nourishment for the likes of the tiny krill that themselves sustain larger sea creatures up to and including the leviathan blue whale.
Here they are thriving on nutrients poured into the Black Sea by the Danube and Dnieper rivers, with energy provided by the warm summer sun.