Envisat captures dust and sand from the Algerian Sahara Desert, located in northern Africa, blowing west across the Atlantic Ocean. Sandstorms are very common over the Sahara, and large concentrations of the dust can be found in the tropical Atlantic and the Caribbean. The dust contains many nutrients, including nitrogen, phosphorus and iron, which act as a fertiliser and stimulate the production of massive plankton blooms. In this image, plankton blooms are visible in the Atlantic as blue and green swirls.
Although some types of plankton are individually microscopic, the chlorophyll they use for photosynthesis collectively tints the colour of the surrounding ocean waters. This allows dedicated 'ocean colour' satellite sensors, such as Envisat's Medium Resolution Imaging Spectrometer (MERIS), to detect them from space. MERIS acquired this image on 8 April 2011 at a resolution of 300 m.