A Turquoise Tint for the Black Sea

Earth Observatory Science Earth Observatory A Turquoise Tint for the Black… Earth Earth Observatory Image of the Day EO Explorer Topics All Topics Atmosphere Land Heat & Radiation Life on Earth Human Dimensions Natural Events Oceans Remote Sensing Technology Snow & Ice Water More Content Collections Global Maps World of Change Articles Earth Matters Blog Blue Marble: Next Generation EO Kids Mission: Biomes About About Us Subscribe 🛜 RSS Contact Us Search June 22, 2026 The Black Sea sits at the boundary between Europe and Asia and connects to the Mediterranean Sea via a chain of waterways. Its surface often appears dark, but each spring and summer it transforms into a striking expanse of swirling turquoise. The OCI (Ocean Color Instrument) on NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite captured this image (above) of the colorful waters on June 22, 2026. The turquoise color is likely caused by coccolithophores, a type of phytoplankton covered with calcium carbonate plates that can give surface waters a milky-blue appearance. These types of phytoplankton tend to dominate in late spring and early summer. Other times of the year, diatoms—a type of microscopic algae with silica shells—can become more prevalent, and they tend to darken the water rather than brighten it. The Bosphorus, the narrow strait running through Istanbul that connects the Black Sea with the Sea of Marmara, also turned turquoise. An astronaut aboard the International Space Station photographed the strait on May 27, 2026 (below), about a month before the PACE image, capturing blooming phytoplankton as it traced currents on both sides of the waterway. (Note that north is oriented toward the bottom of the frame.) May 27, 2026 Though coccolithophores are microscopic, they become so abundant during a bloom that they become visible from space. This makes remote sensing a useful tool for researchers studying bloom dynamics in regions where direct sampling is limited. Beyond t