Each spring and summer, as the air warms up and the sunlight beats down on the Greenland ice sheet, sapphire-colored ponds spring up like swimming pools. As snow and ice melt atop the glaciers, the water flows in channels and streams and collects in depressions on the surface. The ponds provide an important indicator of how much the ice sheet is melting in a given year.
Not only are melt ponds indicators of melt, but they also hint at how fast glaciers will shed ice into the sea. Melt ponds drain to the base of the ice sheet through crevasses. Flowing between the ice and the underlying bedrock, the water lubricates the bottom of the glacier, allowing it to flow more smoothly over the land surface and to shed ice more quickly at the coasts.
Melting also darkens the ice sheet surface. Fresh snow is bright white; when it melts, older and darker ice is exposed. Old ice can be as much as 30 percent less reflective than the younger, brighter snow. The darker old ice absorbs more energy, which leads to more melting and further darkening of the glacial surface.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 188.8.131.52.0