Earth:Ice sheet
In glaciology, an ice sheet, also known as a continental glacier,[2] is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi).[3] The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice sheets are bigger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are termed an ice cap. An ice cap will typically feed a series of glaciers around its periphery.
Although the surface is cold, the base of an ice sheet is generally warmer due to geothermal heat. In places, melting occurs and the melt-water lubricates the ice sheet so that it flows more rapidly. This process produces fast-flowing channels in the ice sheet — these are ice streams.
In previous geologic time spans (glacial periods) there were other ice sheets: during the Last Glacial Period at Last Glacial Maximum, the Laurentide Ice Sheet covered much of North America, the Weichselian ice sheet covered Northern Europe and the Patagonian Ice Sheet covered southern South America.
Definition
An ice sheet is "an ice body originating on land that covers an area of continental size, generally defined as covering >50,000 km2 , and that has formed over thousands of years through accumulation and compaction of snow".[4](p2234)
Common properties
Estimated carbon fluxes are measured in Tg C a−1 (megatonnes of carbon per year) and estimated sizes of carbon stores are measured in Pg C (thousands of megatonnes of carbon). DOC = dissolved organic carbon, POC = particulate organic carbon.[5]
Ice sheets have the following properties: "An ice sheet flows outward from a high central ice plateau with a small average surface slope. The margins usually slope more steeply, and most ice is discharged through fast-flowing ice streams or outlet glaciers, often into the sea or into ice shelves floating on the sea."[4](p2234)
Ice movement is dominated by the motion of glaciers, whose activity is determined by a number of processes.[6] Their motion is the result of cyclic surges interspersed with longer periods of inactivity, on both hourly and centennial time scales.
Until recently, ice sheets were viewed as inert components of the carbon cycle and were largely disregarded in global models. Research in the past decade has transformed this view, demonstrating the existence of uniquely adapted microbial communities, high rates of biogeochemical/physical weathering in ice sheets and storage and cycling of organic carbon in excess of 100 billion tonnes, as well as nutrients (see diagram).[5]
Earth's current two ice sheets
Antarctic ice sheet
Greenland ice sheet
Melting due to climate change
In geologic timescales
Antarctic ice sheet during geologic timescales
Greenland ice sheet during geologic timescales
See also
References
- ↑ "Ice Sheets". National Science Foundation. https://www.nsf.gov/geo/opp/antarct/science/icesheet.jsp.
- ↑ American Meteorological Society, Glossary of Meteorology
- ↑ "Glossary of Important Terms in Glacial Geology". http://gemini.oscs.montana.edu/~geol445/hyperglac/glossary.htm.
- ↑ 4.0 4.1 IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.
- ↑ 5.0 5.1 Wadham, J.L., Hawkings, J.R., Tarasov, L., Gregoire, L.J., Spencer, R.G.M., Gutjahr, M., Ridgwell, A. and Kohfeld, K.E. (2019) "Ice sheets matter for the global carbon cycle". Nature communications, 10(1): 1–17. doi:10.1038/s41467-019-11394-4. 50x50px Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
- ↑ 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.
External links
- United Nations Environment Programme: Global Outlook for Ice and Snow
- http://www.nasa.gov/vision/earth/environment/ice_sheets.html
| |||||||||||||
| |||||||||||||
| |||||||||||||
| |||||||||||||
| |||||||||||||
| |||||||||||||
| |||||||||||||
| |||||||||||||
| |||||||||||||
 |  |
