NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite observed a massive bloom of coccolithophores in the Black Sea on June 22, 2026, turning the water a brilliant turquoise. These microscopic organisms, which possess calcium carbonate plates, create a milky, reflective appearance visible from orbit, playing a significant role in the regional carbon cycle.
The Mechanics of the Black Sea’s Turquoise Shift
The striking color transformation of the Black Sea is primarily driven by coccolithophores. According to NASA, these microscopic phytoplankton are coated in calcium carbonate, the same material found in limestone. When these organisms multiply into massive blooms, their reflective plates scatter sunlight, shifting the water’s appearance from dark to a vivid, milky turquoise.
This biological event is a seasonal staple in the Black Sea. While coccolithophores dominate during the late spring and early summer, other phytoplankton such as diatoms often appear at different times of the year. Unlike the reflective coccolithophores, diatoms—which possess silica shells—typically cause the water to appear darker, creating a sharp contrast in how the sea reflects light depending on the dominant species.
Did you know?
A single coccolithophore is invisible to the human eye without magnification. It is only when they congregate by the millions that their collective light-scattering properties become clearly visible from space.
Tracking Phytoplankton Through Orbital Observation
NASA’s PACE spacecraft, equipped with the Ocean Color Instrument (OCI), provides data that allows researchers to map the distribution of these blooms in real-time. This remote sensing capability is essential for studying areas where physical water sampling is logistically difficult or impossible.
The reach of these blooms is extensive. On May 27, 2026, an astronaut aboard the International Space Station (ISS) captured images of turquoise waters flowing through the Bosphorus strait. These photos reveal how currents dictate the movement of phytoplankton, linking the Black Sea to the Sea of Marmara.
Ecological Impact and the Global Carbon Cycle
These blooms represent more than a visual spectacle; they are a functioning component of the Earth’s carbon cycle. As coccolithophores grow, they absorb carbon dioxide from the environment. When the organisms reach the end of their life cycle, their remains—and the carbon stored within them—sink toward the seafloor.
In the long term, this process acts as a natural carbon sequestration mechanism. By moving carbon from the surface waters to the deep ocean floor, these blooms help regulate atmospheric carbon levels.
Future Trends in Ocean Monitoring
Frequently Asked Questions
- Why does the Black Sea turn turquoise?
It is caused by massive blooms of coccolithophores, which are microscopic algae covered in reflective calcium carbonate plates that scatter light. - How do scientists track these blooms?
NASA uses the PACE satellite’s Ocean Color Instrument to detect light-reflectance patterns, supplemented by high-resolution photography from the International Space Station. - Do these blooms affect the climate?
Yes, coccolithophores absorb carbon during their growth phase, and when they die, they transport that carbon to the seafloor, effectively removing it from the atmosphere.
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