Polar ice cap
A polar ice cap is a high latitude region of a planet or natural satellite that is covered in ice.[1] There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of solid phase matter in the polar region. This causes the term 'polar ice cap' to be something of a misnomer, as the term ice cap itself is applied with greater scrutiny as such bodies must be found over land, and possess a surface area of less than 50,000 km²: larger bodies are referred to as ice sheets.
The composition of the ice will vary. For example Earth's polar ice caps are mainly water ice, while Mars's polar ice caps are a mixture of solid phase carbon dioxide and water ice.
Polar ice caps form because high latitude regions receive less energy in the form of solar radiation from the sun than equatorial regions, resulting in lower surface temperatures.
The Earth's polar ice caps have changed dramatically over the last 12,000 years. Seasonal variations of the ice caps takes place due to varied solar energy absorption as the planet or moon revolves around the sun. Additionally, in geologic time scales, the ice caps may grow or shrink due to climate variation. Ice caps are generally in the negative in temperature.
Contents |
[edit] Earth
-
Extent of the Arctic sea-ice in September, 1978-2002
-
Extent of the Arctic sea-ice in February, 1978-2002
[edit] North Pole
Earth's north pole is covered by floating pack ice (sea ice) over the Arctic Ocean. Portions of the ice that don't melt seasonally can get very thick, up to 3–4 meters thick over large areas, with ridges up to 20 meters thick. One-year ice is usually about a meter thick. The area covered by sea ice ranges between 9 and 12 million km². In addition, the Greenland ice sheet covers about 1.71 million km² and contains about 2.6 million km³ of ice.[2]
According to the National Snow and Ice Data Center, "since 1979, winter Arctic ice extent has decreased about 4.2 percent per decade." Both 2008 and 2009 had a minimum Arctic sea ice extent somewhat above that of 2007. At other times of the year the ice extent is still sometimes near the 1979-2000 average, as in April 2010, by the data from the National Snow and Ice Data Center. [3]
[edit] South Pole
The land mass of the Earth's south pole, in Antarctica, is covered by the Antarctic ice sheet. It covers an area of about 14.6million km² and contains 25-30 million km³ of ice. Around 70% of the fresh water on the Earth is held in this ice sheet. See Climate of Antarctica.
Data from the National Snow and Ice Data Center shows that the sea ice coverage of Antarctica has a slightly positive trend over the last three decades (1979–2009).[4]
[edit] Mars
In addition to Earth, the planet Mars also has polar ice caps. They consist of primarily water-ice with a few percent dust[5]. Frozen carbon dioxide makes up a small permanent portion of the Planum Australe or the South Polar Layered Deposits. In both hemispheres a seasonal carbon dioxide frost deposits in the winter and sublimes during the spring.
Data collected in 2005 from NASA missions to Mars show that the southern residual ice cap undergoes sublimation inter-annually. The most widely accepted explanation is that fluctuations in the planet's orbit are causing the changes.[6]
[edit] See also
[edit] References
- ^ The National Snow and Ice Data Center Glossary
- ^ "NSIDC Arctic Sea Ice News Fall 2007". nsidc.org. http://nsidc.org/news/press/2007_seaiceminimum/20070810_index.html. Retrieved 2008-03-27.
- ^ "Arctic Sea Ice News & Analysis". National Snow and Ice Data Center. http://nsidc.org/arcticseaicenews/. Retrieved 2010-05-09.
- ^ "State of the Cryosphere / Arctic and Antarctic Standardized Anomalies and Trends Jan 1979 - Jul 2009". National Snow and Ice Data Center. http://nsidc.org/sotc/sea_ice.html. Retrieved 2010-04-24.
- ^ Grima, Cyril G.; Kofman, W.; Mouginot, J.; Phillips, R. J.; Herique, A.; Biccardi, D.; Seu, R.; Cutigni, M. (2009). "North polar deposits of Mars: Extreme purity of the water ice". Geophysical Research Letters 36 (3). DOI:10.1029/2008GL036326. http://www.agu.org/pubs/crossref/2009/2008GL036326.shtml.
- ^ Ravilious, Kate (2007-02-28). "Mars Melt Hints at Solar, Not Human, Cause for Warming, Scientist Says". National Geographic News. National Geographic Society. http://news.nationalgeographic.com/news/2007/02/070228-mars-warming.html. Retrieved 2008-10-28.
