Envisat image over Iceland and the Denmark Strait.

The large blue-green areas in the sea off the south and western coasts of Iceland are caused by a very large concentration of phytoplankton. These small organisms form the basis of the ocean's food chain and have an essential role in the global ecosystem: they could help to reduce
the amount of carbon dioxide in the atmosphere, and are a
useful indicator of changes in ocean productivity.

This 21 June 2004 image was acquired by Envisat's Medium Resolution Imaging Spectrometer (MERIS) – an instrument optimised to detect ocean colour - working in full resolution mode with a resolution of 300 metres. The image covers 672 by 672 km.