Antarctica - Geography
Almost 10 percent of the Earth's continental crust resides in Antarctica. The terrain is about 98% thick continental ice sheet and 2% barren rock, with average elevations between 2,000 and 4,000 m; mountain ranges up to nearly 5,000 m; ice-free coastal areas include parts of southern Victoria Land, Wilkes Land, the Antarctic Peninsula area, and parts of Ross Island on McMurdo Sound; glaciers form ice shelves along about half of the coastline, and floating ice shelves constitute 11% of the area of the continent.
The continent is old and stable and has been in a near-polar position for over 100 million years. It thus contains unique high latitude environmental records of a time when Earth changed from greenhouse to icehouse conditions. The landmass is different from the other continents in that Antarctica's crustal structure—or its underlying mantle—has allowed the continent to remain essentially fixed on Earth's surface for a long time.
More than 70 lakes lie beneath the ice sheet, most of them several kilometers long. One, Vostok Subglacial Lake, is an order of magnitude larger and represents the closest analog to both Europa (a moon of Jupiter) and a Neoproterozoic (“Snowball Earth”) subglacial environment. Lake Vostok is likely oligotrophic—an environment with low nutrient levels and low standing stocks of organisms. Life there may depend on alternative energy sources and survival strategies.
The continent itself is depressed more than half a-mile to near sea level under the tremendous load of the ice sheet, with some regions well below sea level. The highest mountains rise to elevations of over 14,000 ft. — about the height of the US Rocky Mountains. Antarctica is composed of two major, geologically distinct parts bridged by a vast ice sheet.
The present Antarctic ice sheet accounts for 90 percent of Earth’s total ice volume and 70 percent of its fresh water. It houses enough water to raise global sea level by 200 ft. if completely melted. The ice sheet at the Pole, nearly two miles thick, is constantly shifting, carrying the facility at the Pole along with it at the rate of about 30 ft. a year. Nearly 90 percent of the ice flowing across West Antarctica converges into ice streams that are the most dynamic, and perhaps unstable, components of the ice sheet.
East Antarctica, the larger of the two, is roughly the size of the US and is composed of continental crust covered by an ice sheet that averages 1.6 miles thick. Rock exposures are limited to isolated coastal regions and to alpine elevations in the 2,000-mile long Transantarctic Mountains. East Antarctica is considerably larger than West Antarctica, and its ice sheet is thick – nearly three miles (five kilometers) in some regions. The ice surface of East Antarctica is high and home to some of the coldest and driest condition on Earth.
West Antarctica, the smaller portion, is a mosaic of small blocks of continental crust covered by the West Antarctic Ice Sheet [WAIS] and an Andean-like mountain chain forming the Antarctic Peninsula. Most of the West Antarctic Ice Sheet is grounded below sea level, in places over 1.5 miles below sea level. Recent studies of West Antarctica found that many of its fast-moving glaciers are in an irreversible decline. Numerical models suggests that a full-scale collapse of this sector of the West Antarctic Ice Sheet may be inevitable. But they leave a large uncertainty in the timing; more complex coupled ice-sheet and climate models are needed to model this more thoroughly in the future. Recent glaciological observations have yielded evidence that some of these West Antarctic ice streams may be responding to climatic and sea level changes of the recent past, changes that could lead to more rapid retreat and global sea-level rise in the future. A few active volcanoes may also affect the ice sheet’s behavior.
Large portions of the West Antarctic Ice Sheet (WAIS) are grounded on bedrock below sea level. These so-called marine parts of the ice sheet hold an ice volume that would elevate global mean sea level by about 3.3 m. The bed below this marine ice is generally down-sloping in the inland direction. A grounding line (the line that separates the grounded ice sheet from the floating ice shelf) that is located on such bed has been shown to be potentially unstable. The associated marine ice-sheet instability (i.e., self-sustained ice-sheet retreat) can be hindered by the buttressing of ice shelves.
Time evolution of the sea-level contribution after the beginning of the perturbation of the equilibrium ice sheet shows global sea-level rise of up to 0.02 meters by around the year 2100 AD, and up to 3 meters by around the year 12,000 AD.
The Antarctic Peninsula is probably Antarctica’s most prominent geographical feature and home to scientific stations operated by the United States, the United Kingdom, France, Australia, and other nations. This curved extension of the continent extends nearly 250 miles north of the Antarctic Circle and points toward the southern tip of South America. The Antarctic Peninsula has a number of glaciers and floating ice shelves that are changing rapidly because this region is warming faster than the rest of the continent.
Running along the length of the peninsula, and extending across the continent is a mountain chain known as the Transantarctic Mountains. In addition to supplying spectacular views, the Transantarctics serve as a sort of dividing line separating East and West Antarctica. The West Antarctic and East Antarctic ice sheets are separated by the Transantarctics, with ice on the west side generally flowing toward the Western Hemisphere and ice on the east side flowing toward the eastern hemisphere. (In both cases, this is actually flowing north…away from the South Pole.)
|Join the GlobalSecurity.org mailing list|