The Black Sea has turned turquoise, a phenomenon clearly visible in NASA satellite images. Scientists explain that this occurrence is linked to the mass blooming of a specific type of phytoplankton.
Black Sea on June 22 / © NASA
Every spring and early summer, the Black Sea transforms its usual dark hue into a vibrant turquoise due to the extensive proliferation of phytoplankton. NASA’s PACE satellite has documented precisely this natural event.
NASA reported this, releasing a satellite snapshot captured by the Ocean Color Instrument (OCI) aboard the PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem) satellite on June 22. The image clearly shows a significant portion of the Black Sea’s surface displaying a rich turquoise shade.
NASA scientists have indicated that the unusual water color is likely caused by coccolithophores, a variety of phytoplankton covered in calcium carbonate plates. It is these microscopic organisms, during their mass blooms, that can impart a milky blue or turquoise tint to the sea’s surface. They are most frequently dominant in the waters during late spring and early summer.
During other seasons, the situation shifts. According to NASA, diatoms—microscopic algae with silica shells—become more prevalent in the Black Sea. Unlike coccolithophores, they do not brighten the water; on the contrary, they render it darker.
The Bosporus Strait, a narrow passage that traverses Istanbul and links the Black Sea with the Sea of Marmara, has also taken on a turquoise color. As far back as May 27, 2026, an astronaut aboard the International Space Station photographed phytoplankton blooms in the strait. The image depicted how currents carried the bloom on both sides of the waterway.
Black Sea on May 27 / © NASA
NASA explains that despite the microscopic size of coccolithophores, their concentration becomes so high during mass blooms that the change in water color is discernible even from satellites. This is why space-based observations are crucial for scientists in tracking phytoplankton distribution, particularly in areas where regular water sampling is challenging.
Beyond the visual spectacle, these blooms play a vital role in the ocean’s carbon cycle. When coccolithophores perish, a portion of the carbon they absorbed sinks to the seabed, where it can remain sequestered for extended periods.
We previously reported that the Tuzly Estuaries National Nature Park announced a mass die-off of dolphins in the Black Sea, with 56 deceased animals recorded in one month. Additionally, cetaceans showing signs of contusion were found near Odesa.
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