Recent measurements of the thinning of the Greenland Ice Sheet

Continental ice sheets contain a large amount of water which if melted could have a significant impact on sea level. Therefore, it is important to know if the polar ice sheets are growing or melting. A comparison of aerial surveys of the southern Greenland ice sheet in 1993 and 1998 indicate that overall the mass balance of the Greenland ice sheet is negative, meaning that the Greenland ice sheet is thinning. The largest thinning rates are in the southeast section where outlet glaciers are thinning at a rate of about 1 m per year. This thinning corresponds with observations of warmer temperatures between 1993 and 1998. However at most of the lower elevations (below 2000m above sea level) there is a thinning, including the western region which has had cooler temperatures than normal. At higher elevations a thickening of the ice sheet of 0.5 0.7 cm/year has been measured from 1993 to 1998. Despite this, the overall balance is negative, resulting in an overall decrease in the size of Greenland. The large magnitude of this thinning is too great to be the result of reduced snowfall and increased melting alone. It is thought that the melt water from the surface of the glacier is filtering down to the bottom of the ice sheet where it is acting as a lubricator, allowing the glacier to slide against the bedrock more easily and quickly, moving the ice out into the sea. This was reported by Krabill, Frederick, Manizade, Martin, Sonntag, Swift, Thomas, Wright and Yungel, in Science magazine on March 5, 1999 in a paper entitled "Rapid Thinning of Parts of the Southern Greenland Ice Sheet"


Credit: Reprinted with permission from Krabill, Frederick, Manizade, Martin, Sonntag, Swift, Thomas, Wright and Yungel, "Rapid Thinning of Parts of the Southern Greenland Ice Sheet", Science, 283, No. 5407, 1522-1524, March 5, 1999. Copyright 1999 American Association for the Advancement of Science

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