The dark waters of the Black Sea were colored with swirls of green and blue, indicating the presence of both sediment and phytoplankton, in late April 2013. The Black Sea drainage basic encompasses almost 1/3 of Europe, with the Danube River running through 10 countries alone. Each year an estimated 350 km3 of runoff enters the Black Sea, bringing substantial sediment into the semi-enclosed waters. Where sediment-laden rivers flow into the Sea, the waters appear tan and quickly fade to green, as the sediment sinks. This can be clearly seen at the outflow of the Danube River in the northwest section of the Sea. Also, a large amount of sediment discolors the Sea of Azov (north).
Much of the Black Sea drainage basin, as well land immediately surrounding the Sea, are agricultural areas, and fertilization of the land is frequent. Runoff carries fertilizers into the Sea, spurring the growth of phytoplankton (microscopic plant-like organisms) which can reproduce rapidly in jewel-toned blooms which can be easily seen from space. The milky-blue swirls which color the eastern part of the Sea are typical colors for phytoplankton; however, the green tones near the river outflows may well reflect not only sediment, but also phytoplankton growth.
The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite captured this true-color image on April 28.