This Envisat image, acquired on 12 August 2008 with the Medium Resolution Imaging Spectrometer (MERIS) instrument, captures a plankton bloom stretching across the Northeast Passage in the Barents Sea. Plankton, the most abundant type of life found in the ocean, are microscopic marine plants that drift on or near the surface of the sea. Microscopic plankton have been called 'the grass of the sea' because they are the basic food on which all other marine life depends. Although some types of plankton are individually microscopic, the chlorophyll they use for photosynthesis collectively tints the colour of the surrounding ocean waters, providing a means of detecting these tiny organisms from space with dedicated 'ocean colour' sensors, such as MERIS, onboard satellites.