The Black Sea has turned turquoise, a phenomenon clearly visible in NASA satellite imagery. Scientists attribute this occurrence to the massive bloom of a specific type of phytoplankton.
The Black Sea on June 22 / © NASA
Every spring and early summer, the Black Sea transforms from its usual dark hue to a vibrant turquoise due to extensive phytoplankton blooms. This natural event was recently captured by NASA’s PACE satellite.
NASA announced this, releasing a satellite picture acquired on June 22 using the Ocean Color Instrument (OCI) aboard the PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem) satellite. The image reveals a substantial portion of the Black Sea’s surface displaying a rich turquoise shade.
NASA scientists explained that the unusual water color is likely caused by coccolithophores, a species of phytoplankton covered in calcium carbonate plates. When these microscopic organisms bloom en masse, they can impart a milky blue or turquoise tint to the sea’s surface. They are most prevalent in the body of water in late spring and early summer.
During other times of the year, the situation shifts. According to NASA, diatoms—microscopic algae with silica shells—become more dominant in the Black Sea. Unlike coccolithophores, diatoms do not lighten the water; on the contrary, they tend to darken it.
The Bosphorus, a narrow strait that runs through Istanbul and connects the Black Sea to 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 a phytoplankton bloom in the strait. The image showed how currents carried it along both sides of the waterway.
The Black Sea on May 27 / © NASA
NASA clarifies that despite the microscopic size of coccolithophores, their concentration during a mass bloom becomes so high that the change in water color is detectable even from satellites. This is why space-based observations are invaluable for scientists tracking phytoplankton distribution, especially in regions where regular water sampling is challenging.
Beyond their visual impact, these blooms play a crucial 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 on the mass mortality of dolphins in the Black Sea at the Tuzlivski Lymany National Nature Park. Fifty-six deceased animals were recorded in one month. Additionally, cetaceans exhibiting signs of contusion were found near Odesa.
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Source: tsn.ua