For Ukrainians, the Black Sea is not merely a geographical boundary to the south but a fundamental component of our natural environment. We have become accustomed to its profound, occasionally severe, leaden-dark waters that truly embody their name. Nonetheless, each spring and summer, our sea presents a magnificent natural display, transforming into a vibrant turquoise expanse comparable to tropical resorts. This remarkable metamorphosis is most effectively observed from space.
On June 22, 2026, NASA’s latest satellite, PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem), acquired remarkable images of the Black Sea utilizing its highly sensitive OCI instrument. Instead of the typical dark expanse, the cameras documented large whirlpools in shades of milky blue and turquoise.
This “color anomaly’ extended beyond the open sea and was observed as far as the Bosphorus. On May 27 of the same year, astronauts aboard the International Space Station captured images of these luminous currents traversing the strait that links the Black Sea to the Sea of Marmara, forming intricate patterns on the water.
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Introducing coccolithophores, a category of microscopic phytoplankton that predominantly thrive in oceanic environments during warmer seasons. The distinguishing characteristic of these diminutive organisms is their distinctive “armor,” composed of minuscule plates of calcium carbonate, akin to common chalk. During extensive blooms where billions congregate, sunlight reflects off their shells, imparting a vivid turquoise coloration to the water.
Interestingly, during the colder months, other microorganisms — diatoms — become predominant in the sea. Their shells are composed of silicon, and it is these diatoms that cause the water to appear more murky and darker, thereby reaffirming the historic “black” reputation of our sea.
Not merely aesthetics, but also environmental preservation
Although individual algae are imperceptible to the human eye, the magnitude of their blooms is sufficiently extensive to be detected from orbit. For Ukrainian and international researchers, this represents a significant advancement: satellite surveillance enables the observation of life within the Black Sea even in regions where conventional scientific expeditions by vessel are presently unfeasible or hazardous due to ongoing conflict.
Phytoplankton plays a crucial role in the Earth’s carbon cycle. During its brief lifespan, it absorbs carbon dioxide from the atmosphere via photosynthesis. Upon death, a portion of the organic matter descends to the seabed. In the Black Sea, distinctive conditions facilitate this process: the deep waters are nearly anoxic, thereby considerably delaying the decomposition of organic material. Consequently, some of the absorbed carbon persists for extended periods within the sediment layers. Additionally, coccolithophores — microscopic algae characterized by calcareous plates — further contribute to carbon sequestration in mineral form.
We previously demonstrated the appearance of the Danube Delta from satellite imagery.
Provided by NASA
