With the return of summer and the sudden rise in temperatures, there is at least one species that seems to benefit from the heat. The Black Sea has in fact been covered with fascinating turquoise blue arabesques: a natural spectacle that repeats itself every year, so vast that it is visible from space, reports The Debrief.
Located on the border between Europe and Asia, the Black Sea is connected to the Mediterranean by a succession of straits and small inland seas. Although its surface generally appears dark, each spring and early summer it takes on a spectacular blue-green color, visible from thousands of kilometers.
These formations, drawn by ocean currents, were first noted by astronauts on the International Space Station (ISS) last May, before being observed by NASA’s PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem) satellite on June 22. Dedicated to the study of phytoplankton, aerosols and clouds, this Earth observation mission launched in 2024 makes it possible to document, among other things, the proliferation of these marine microorganisms, called coccolithophores.
These tiny algae, invisible to the naked eye, have a particularity: they are covered with fine plates of calcium carbonate, coccoliths, a major component found in shells or chalk. Thanks to their abundance and presence in oceans around the world, these organisms are responsible for almost half of marine limestone production. When their numbers explode in the face of rising temperatures, these plates strongly reflect sunlight, giving the water this astonishing turquoise hue.
Perfect conditions
A study conducted in 2018 by the University of California showed that this species was relatively resistant to ocean acidification, one of the consequences of global warming. If this growth is favored by rising temperatures, coccolithophores also depend on the supply of nutrients. In summer, the warming of the waters, combined with the minerals transported by rivers from the land, provides ideal conditions and an environment conducive to their development.
Beyond the aesthetic aspect, these blooms have an essential role in the food chain, since certain small fish consume them, but also in the natural carbon cycle of the planet. Through photosynthesis, they capture carbon dioxide (CO2) present in the atmosphere. When they die, some of the absorbed carbon sinks with them to the seabed, where it can remain stored for very long periods.
The phenomenon is not limited to the Black Sea. Earlier this year, a similar bloom was observed off the east coast of the United States, where warming waters and the arrival of nutrients from melting snow also favored the development of coccolithophores.
More recently, the waters of the Bosphorus, a strait which crosses Istanbul and connects the Black Sea to the Sea of Marmara, have also been tinged with turquoise.
