NASA Satellite Captures Massive Turquoise Algae Bloom in Black Sea

The Science Behind the Color

The striking turquoise hue is caused by massive blooms of coccolithophores, a type of microscopic phytoplankton. While individual coccolithophores are far too small to be seen with the naked eye, they possess unique biological characteristics that become visible from space when the organisms multiply in enormous numbers. Each coccolithophore cell is coated in plates made of calcium carbonate. When these organisms bloom during late spring and early summer, their reflective, hubcap-shaped shells scatter sunlight, giving the surface of the water a milky-blue or turquoise appearance. This biological display contrasts with other periods of the year when different microscopic algae, known as diatoms, dominate the region. Unlike coccolithophores, diatoms have shells made of silica and generally cause the Black Sea to appear darker rather than brighter.

Bosphorus Strait Affected

The bloom was not confined to the open waters of the Black Sea. The Bosphorus, the narrow waterway that runs through Istanbul and links the Black Sea to the Sea of Marmara, also experienced the shift in color. On May 27, 2026—nearly a month before the PACE satellite captured the wider view—a member of the Expedition 74 crew aboard the International Space Station photographed the strait. The images show blooming phytoplankton tracing swirling currents on both sides of the channel. The photograph was acquired using a Nikon Z9 camera with a 50-millimeter focal length and was later provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit at NASA Johnson Space Center.

Ecological Importance and the Carbon Cycle

Beyond their aesthetic impact, these phytoplankton blooms play a critical role in the health of marine ecosystems and the global carbon cycle. Phytoplankton serve as the foundation of marine food webs, providing a primary food source for organisms ranging from tiny zooplankton to fish and whales. Furthermore, these blooms are essential to the planet’s carbon management. As coccolithophores grow, they absorb carbon from the atmosphere and the surrounding water through photosynthesis. When the organisms die, a portion of that carbon sinks to the seafloor along with their calcium carbonate plates. This process allows carbon to be stored in ocean sediments for long periods, effectively transferring it from the surface ocean into long-term storage.

Monitoring Marine Health from Orbit

Because these blooms are easily detected from orbit, satellite observations provide scientists with a vital tool for monitoring marine ecosystems, particularly in regions where collecting direct water samples is difficult. The PACE mission was specifically designed to observe these biological processes. Its Ocean Color Instrument can distinguish subtle differences in water color that earlier satellites could not easily detect. By providing repeated, wide-angle views, the satellite allows researchers to track how blooms develop, spread, and dissipate over time. These observations help scientists monitor environmental shifts, including changes in water temperature, nutrient availability, and circulation patterns. Understanding these dynamics is increasingly important as researchers work to predict how Earth’s climate system and marine biodiversity will respond to future environmental changes. The image of the Black Sea bloom was produced by NASA Earth Observatory using data from the NASA Ocean Biology Distributed Active Archive Center (OB.DAAC), NASA EOSDIS LANCE, and GIBS/Worldview.

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