Surface ice of the Greenland Ice Sheet (IMAGE) University of Bristol Caption Surface ice of the Greenland Ice Sheet within the 'dark-zone' that runs along the western ice sheet margin. The purple/brown discolouration of the ice is driven by a bloom of microscopic 'glacier algae' that produce a specialist 'sun-screen' pigment to protect themselves from the excess sunlight and low temperatures that characterize this environment. Credit Dr Chris Williamson Usage Restrictions Single use only for use with the press release. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.