Along the top of this satellite image lies the coast of South Africa, but follow the sheets of clouds south about 500 miles, and a beautiful, incongruous-looking blue swirl appears. That plankton-laced eddy, which is 90 miles wide, is the oceanic version of a storm, spun off from a larger current and caused by roiling of water instead of air. Eddies in this region bring warm water from the Indian Ocean to the South Atlantic, and they can even pull nutrients up from the deep sea, fertilizing surface waters and causing blooms of plankton in areas that are otherwise rather devoid of life. It is just such a bloom that lends this eddy its cerulean hue.
Image courtesy of NASA’s Earth Observatory