Ice shelf: Difference between revisions
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* http://www.antdiv.gov.au/default.asp?casid=1547 - from the Australian Antarctic Division |
* http://www.antdiv.gov.au/default.asp?casid=1547 - from the Australian Antarctic Division |
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* http://nsidc.org/iceshelves - from the U.S. National Snow and Ice Data Center |
* http://nsidc.org/quickfacts/iceshelves.html - from the U.S. National Snow and Ice Data Center |
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* http://www.cnn.com/2006/TECH/science/12/29/canada.arctic.ap/index.html - CNN story about the Canadian Ayles ice shelf break up in August 2005 |
* http://www.cnn.com/2006/TECH/science/12/29/canada.arctic.ap/index.html - CNN story about the Canadian Ayles ice shelf break up in August 2005 |
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* http://ice-glaces.ec.gc.ca/ - from the Canadian Ice Service |
* http://ice-glaces.ec.gc.ca/ - from the Canadian Ice Service |
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Revision as of 20:18, 10 August 2010
An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are found in Antarctica, Greenland and Canada only. The boundary between the floating ice shelf and the grounded (resting on bedrock) ice that feeds it is called the grounding line. The thickness of ice shelves ranges from about 100 to 1000 meters.
In contrast, sea ice is formed on water, is much thinner (typically less than 3m), and forms throughout the Arctic Ocean. It also is found in the Southern Ocean around the continent of Antarctica.
Ice shelves are principally driven by gravity-driven pressure from the grounded ice [1] That flow continually moves ice from the grounding line to the seaward front of the shelf. The primary mechanism of mass loss from ice shelves is iceberg calving, in which a chunk of ice breaks off from the seaward front of the shelf. Typically, a shelf front will extend forward for years or decades between major calving events. Snow accumulation on the upper surface and melting from the lower surface are also important to the mass balance of an ice shelf. Ice may also accrete onto the underside of the shelf.
The density contrast between glacial ice, which is denser than normal ice, and liquid water means that only about 1/9 of the floating ice is above the ocean surface. The world's largest ice shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf in Antarctica.
The term captured ice shelf has been used for the ice over a subglacial lake, such as Lake Vostok.
Canadian ice shelves
All Canadian ice shelves are attached to Ellesmere Island and lie north of 82°N. Ice shelves that are still in existence are the Alfred Ernest Ice Shelf, Milne Ice Shelf, Ward Hunt Ice Shelf and Smith Ice Shelf. The Ayles Ice Shelf broke up in 2005, M'Clintock Ice Shelf broke up from 1963 to 1966 and Markham Ice Shelf broke up in 2008.
Antarctic ice shelves
See also: List of Antarctic ice shelves
A total of 44 percent of the Antarctic coastline has ice shelves attached. Their aggregate area is 1,541,700 km² [1].
Ice shelf disruption
In the last several decades, glaciologists have observed consistent decreases in ice shelf extent through melt, calving, and complete disintegration of some shelves.[2]
The Ellesmere ice shelf reduced by 90 percent in the twentieth century, leaving the separate Alfred Ernest, Ayles, Milne, Ward Hunt, and Markham Ice Shelves. A 1986 survey of Canadian ice shelves found that 48 km². (3.3 cubic kilometers) of ice calved from the Milne and Ayles ice shelves between 1959 and 1974.[3] The Ayles Ice Shelf calved entirely on August 13, 2005. The Ward Hunt Ice Shelf, the largest remaining section of thick (>10 m) landfast sea ice along the northern coastline of Ellesmere Island, lost 600 square km of ice in a massive calving in 1961-1962.[4] It further decreased by 27% in thickness (13 m) between 1967 and 1999.[5] In summer 2002, the Ward Ice Shelf experienced another major breakup. [6]
Two sections of Antarctica's Larsen Ice Shelf broke apart into hundreds of unusually small fragments (100's of meters wide or less) in 1995 and 2002.
The breakup events may be linked to the dramatic polar warming trends that are part of global warming. The leading ideas involve enhanced ice fracturing due to surface meltwater and enhanced bottom melting due to warmer ocean water circulating under the floating ice.
The cold, fresh water produced by melting underneath the Ross and Flichner-Ronne ice shelves is a component of Antarctic Bottom Water.
Although it is believed that the melting of floating ice shelves will not raise sea levels, technically, there is a small effect due to the fact that sea water is ~2.6% more dense than fresh water combined with the fact that ice shelves are overwhelmingly "fresh" (having virtually no salinity); this causes the volume of the sea water needed to displace a floating ice shelf to be slightly less than the volume of the fresh water contained in the floating ice. Therefore, when a mass of floating ice melts, sea levels will increase; however, this effect is small enough that if all extant sea ice and floating ice shelves were to melt, the corresponding sea level rise is estimated to be ~4 cm. [7][8][9]
References
- ^ Greve, R.; Blatter, H. (2009). Dynamics of Ice Sheets and Glaciers. Springer. doi:10.1007/978-3-642-03415-2. ISBN 978-3-642-03414-5.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ "Antarctic ice shelf 'hanging by thread': European scientists". July 10, 2008. Yahoo! News.
- ^ Jeffries, Martin O. Ice Island Calvings and Ice Shelf Changes, Milne Ice Shelf and Ayles Ice Shelf, Ellesmere Island, N.W.T.. Arctic 39 (1) (March 1986)
- ^ Hattersley-Smith, G. The Ward Hunt Ice Shelf: recent changes of the ice front. Journal of Glaciology 4:415-424. 1963.
- ^ Vincent, W.F., J.A.E. Gibson, M.O. Jeffries. Ice-shelf collapse, climate change, and habitat loss in the Canadian high Arctic. Polar Record 37 (201): 133-142 (2001)
- ^ NASA Earth Observatory. "Breakup of the Ward Hunt Ice Shelf".
- ^ Peter Noerdlinger, PHYSORG.COM "Melting of Floating Ice Will Raise Sea Level"
- ^ Noerdlinger, P.D. (2007). "The melting of floating ice raises the ocean level". Geophysical Journal International. 170 (1): 145–150. doi:10.1111/j.1365-246X.2007.03472.x.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help); Unknown parameter|month=ignored (help)CS1 maint: unflagged free DOI (link) - ^ Jenkins, A. (2007). "Melting of floating ice and sea level rise". Geophysical Research Letters. 34 (16): L16609. doi:10.1029/2007GL030784.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help); Unknown parameter|month=ignored (help)
See also
Ice sheet dynamics Wikinews
External links
- http://www.antdiv.gov.au/default.asp?casid=1547 - from the Australian Antarctic Division
- http://nsidc.org/quickfacts/iceshelves.html - from the U.S. National Snow and Ice Data Center
- http://www.cnn.com/2006/TECH/science/12/29/canada.arctic.ap/index.html - CNN story about the Canadian Ayles ice shelf break up in August 2005
- http://ice-glaces.ec.gc.ca/ - from the Canadian Ice Service