Antarctic Ice Sheets

ICE COVERS MUCH of the polar regions of Earth, and is a critical component to the planets climate. An ice sheet is defined as a mass of ice that is greater than 31,067 mi. (50,000 km.) in area, such as those of Antarctica and Greenland. Ice sheets should not be confused with ice caps, which are masses of ice covering less than 31,067 mi. (50,000 km.) in area. It is estimated that approximately 90 percent of the Earths total ice mass, or 27 million cu. km., is located in the Antarctic Ice Sheet. Scientists are concerned that increasing temperatures of air and sea will cause significant melting of the worlds ice, including the Antarctic Ice Sheets, causing sea level rise.

Ice sheets, glaciers, ice caps, permafrost, snow, and sea ice are all components of the Earths cryosphere (portions of the Earths surface that are frozen over land or water). In the Southern Hemisphere, the Antarctic Ice Sheet covers approximately 98 percent of the Antarctic continent and is the single largest mass of ice on the planet. Ice sheets form as snow and frost build up in an area, compressing the previously fallen snow into ice. The total area of ice sheets is changed regularly by melting, primarily where the ice comes into contact with water or warmer dry land at its base, and by calving, or the falling off of large pieces of the ice sheet, which become known as icebergs. The Antarctic ice sheet covers the major landmass of the continent in the eastern Antarctic and extends over the ocean in western Antarctica. In western Antarctica, the ice sheet is as deep as 8,202 ft. (2,500 m.) below sea level.

The Antarctic continent is cold year round, and is extremely dry (desert; little to no annual precipitation). Because of this, the Antarctic ice sheet has historically experienced very little melting from the surface. Typically, the summertime melt that is experienced by the ice sheet is focused around the northern Antarctic Peninsula and the northeasternmost regions of the ice sheet. Most ice from the Antarctic ice sheet is lost by calving of glaciers from the protruding ice shelves of the sheet.

With climate in a constant state of flux on Earth, scientists have begun to give considerable attention to the warming trends that appear to exceed normal climate oscillations. While gradual melting and refreezing of ice is common anywhere on Earth, sudden large-scale melting of the polar ice sheets may have significant implications for local and global ecosystems. It is believed that the interaction of warming ocean waters and increasing air temperatures is contributing to the thinning and breaking up of the ice sheets. This disturbance of the ice sheets, and glacier tongues (extension of glaciers projecting seaward, typically afloat), primarily in western Antarctica at the ocean interface, has increased floating ice (drift ice), changing the ecosystem structure of [Page 62]this sensitive region. Long term, such disturbances may have a significant impact on macrofauna, such as seals and whales, which are dependent on the ice sheet-water interface for feeding.

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