Phytoplankton Give the Black Sea a Turquoise Tint

The Black Sea, which sits between Europe and Asia and connects to the Mediterranean through a chain of waterways, often looks dark at the surface. On June 22, 2026, the Ocean Color Instrument aboard NASA’s PACE satellite captured a striking transformation: large swaths of water turned a milky turquoise.

The color comes from coccolithophores, tiny phytoplankton coated in calcium carbonate plates that can lend surface waters a pale, milky-blue cast. These organisms tend to dominate in late spring and early summer; at other times of year, diatoms with silica shells can prevail and darken the water instead.

The narrow Bosphorus Strait near Istanbul also showed turquoise blooms. An astronaut aboard the International Space Station photographed the strait on May 27, 2026, about a month before the PACE image, capturing coccolithophore blooms as they traced currents on both sides of the waterway (north is toward the bottom of that frame).

Turkey, Istanbul

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