The Black Sea lies between Europe and Asia, is connected to the Mediterranean Sea through a series of waterways, and is known for its dark waters. But each spring and summer, large areas undergo a surprising transformation, turning a vibrant turquoise color. On June 22, 2026, NASA’s PACE (Plankton, Aerosols, Clouds, and Marine Ecosystems) satellite captured this colorful seasonal display using the Ocean Color Instrument (OCI).
Scientists believe this striking turquoise color comes from blooms of coccolithophytes, microscopic phytoplankton covered with plates of calcium carbonate. When these creatures multiply in huge numbers from late spring to early summer, their reflective shells scatter sunlight, creating a milky-white ocean that can be seen from space.
At other times of the year, various microalgae called diatoms are more abundant. Unlike coccolithophytes, diatoms have silica shells that generally make the Black Sea appear darker instead of brighter.
The Bosphorus also shines turquoise.
This seasonal flower has spread all the way to the Bosphorus, the narrow waterway that flows through Istanbul and connects the Black Sea and the Sea of Marmara. On May 27, 2026, about a month before the PACE satellite captured the widespread scene, astronauts aboard the International Space Station photographed the strait as blooming phytoplankton traced swirling currents on both sides of the strait. (Note that north is toward the bottom of the frame.)
Why are these flowers important?
Individual coccolithophytes are too small to be seen with the naked eye, but when their populations become very dense, they can change the color of entire areas of the ocean. Because these blooms are easily detected from orbit, satellite observations provide scientists with an important way to monitor marine ecosystems in areas where collecting water samples is difficult.
These phytoplankton also play an important role in the earth’s carbon cycle. As they grow, they absorb carbon from the atmosphere and surrounding water. After they die, some of that carbon sinks to the ocean floor, where it remains stored for long periods of time, helping to move carbon from the surface ocean to long-term storage.
NASA Earth Observatory created the satellite images using PACE data from NASA EOSDIS LANCE, GIBS/Worldview, and NASA Ocean Biology Distributed Active Archive Center OB.DAAC. Astronaut photo (ISS074-E-619520) was taken by members of the Expedition 74 crew on May 27, 2026 using a Nikon Z9 camera with a 50-millimeter focal length. Images were cropped, enhanced to improve contrast, and corrected to remove lens artifacts.
This photo was provided by the ISS Crew Earth Observation Facility and the Earth Science and Remote Sensing Unit at NASA Johnson Space Center. Through the International Space Station Program and the ISS National Laboratory, astronauts regularly capture images of Earth that support scientific research and make them freely available to researchers and the public. Additional photos taken by astronauts and astronauts can be viewed through NASA/JSC’s Gateway to Earth Astronaut Photos.
