Ice shelf#Antarctic ice shelves

File:Larsen Ice Shelf in Antarctica.jpg grounding line along the Foyn Coast of the Antarctic Peninsula. The floating ice shelf is in the left foreground, and the grounding line is visible as an abrupt change in surface slope due to flexure caused by the buoyancy force where the ice reaches flotation.]]

An ice shelf is a large platform of glacial ice floating on the ocean, fed by one or multiple tributary glaciers. Ice shelves form along coastlines where the ice thickness is insufficient to displace the more dense surrounding ocean water. The boundary between the ice shelf (floating) and grounded ice (resting on bedrock or sediment) is referred to as the grounding line; the boundary between the ice shelf and the open ocean (often covered by sea ice) is the ice front or calving front.

Ice shelves are found in Antarctica and the Arctic (Greenland, Northern Canada, and the Russian Arctic), and can range in thickness from about {{cvt|100-1000|m|ft}}. The world's largest ice shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf in Antarctica.

The movement of ice shelves is principally driven by gravity-induced pressure from the grounded ice.{{cite book |author1=Greve, R. |author2=Blatter, H. |year=2009 |title=Dynamics of Ice Sheets and Glaciers |publisher=Springer |doi=10.1007/978-3-642-03415-2 |isbn=978-3-642-03414-5}} That flow continually moves ice from the grounding line to the seaward front of the shelf. Typically, a shelf front will extend forward for years or decades between major calving events (calving is the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, ice shelf, or crevasse).[http://ebeltz.net/glacier/glacglos.html Glossary of Glacier Terms], Ellin Beltz, 2006. Retrieved July 2009.Essentials of Geology, 3rd edition, Stephen Marshak 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 effects of climate change are visible in the changes to the cryosphere, such as reduction in sea ice and ice sheets, and disruption of ice shelves. In the last several decades, glaciologists have observed consistent decreases in ice shelf extent through melt, calving, and complete disintegration of some shelves. Well studied examples include disruptions of the Thwaites Ice Shelf, Larsen Ice Shelf, Filchner–Ronne Ice Shelf (all three in the Antarctic) and the disruption of the Ellesmere Ice Shelf in the Arctic.

Definition

File:Moa iceshelves.jpg

File:Antarctic Sound-2016-Joinville Island-Ice Shelf.jpg from Joinville Island]]

An ice shelf is "a floating slab of ice originating from land of considerable thickness extending from the coast (usually of great horizontal extent with a very gently sloping surface), resulting from the flow of ice sheets, initially formed by the accumulation of snow, and often filling embayments in the coastline of an ice sheet."IPCC, 2021: Annex VII: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Glossary] [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. In [https://www.ipcc.ch/report/ar6/wg1/ 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.{{Rp|page=2234}}

In contrast, sea ice is formed on water, is much thinner (typically less than {{cvt|3|m|ft}}), and forms throughout the Arctic Ocean. It is also found in the Southern Ocean around the continent of Antarctica.

The term captured ice shelf has been used for the ice over a subglacial lake, such as Lake Vostok.

Properties

File:Ross Ice Shelf 1997.jpg

Ice shelves are thick plates of ice, formed continuously by glaciers, that float atop an ocean. The shelves act as "brakes" for the glaciers. These shelves serve another important purpose—"they moderate the amount of melting that occurs on the glaciers' surfaces. Once their ice shelves are removed, the glaciers increase in speed due to meltwater percolation and/or a reduction of braking forces, and they may begin to dump more ice into the ocean than they gather as snow in their catchments. Glacier ice speed increases are already observed in Peninsula areas where ice shelves disintegrated in prior years."{{cite web |title=Larsen B Ice Shelf Collapses in Antarctica – National Snow and Ice Data Center |url=https://nsidc.org/news/newsroom/larsen_B/2002.html |access-date=20 April 2019 |website=nsidc.org |archive-date=14 July 2017 |archive-url=https://web.archive.org/web/20170714061003/http://nsidc.org/news/newsroom/larsen_B/2002.html |url-status=dead }}

= Height =

The density contrast between glacial ice and liquid water means that at least {{sfrac|9}} of the floating ice is above the ocean surface, depending on how much pressurized air is contained in the bubbles within the glacial ice, stemming from compressed snow. The formula for the denominators above is $1/[(\rho_\text{seawater} - \rho_\text{glacial ice})/\rho_\text{seawater}]$ , density of cold seawater is about 1028 kg/m³ and that of glacial ice from about 850 kg/m³{{Cite web |last=Pidwirny |first=Michael |date=2006 |title=Glacial Processes |url=http://www.physicalgeography.net/fundamentals/10ae.html |access-date=2018-01-21 |website=www.physicalgeography.net}}{{Cite journal |last=Shumskiy |first=P. A. |date=1960 |title=Density of Glacier Ice |journal=Journal of Glaciology |volume=3 |issue=27 |pages=568–573 |bibcode=1960JGlac...3..568S |doi=10.3189/S0022143000023686 |issn=0022-1430 |doi-access=free}} to well below 920 kg/m³, the limit for very cold ice without bubbles.{{Cite web |date=2009-09-11 |title=Densification |url=http://www.iceandclimate.nbi.ku.dk/research/flowofice/densification/ |access-date=2018-01-21 |website=www.iceandclimate.nbi.ku.dk |language=en |archive-date=2018-01-22 |archive-url=https://web.archive.org/web/20180122075048/http://www.iceandclimate.nbi.ku.dk/research/flowofice/densification/ |url-status=dead }}{{Cite web |title=Ice – Thermal Properties |url=https://www.engineeringtoolbox.com/ice-thermal-properties-d_576.html |access-date=2018-01-21 |website=www.engineeringtoolbox.com |language=en}} The height of the shelf above the sea can be even larger, if there is much less dense firn and snow above the glacier ice.

By country or region

=== Antarctica ===

File:Antarctic Grows.jpg differentiating its landmass (dark grey), ice shelves (light grey), and sea ice (white){{Cite web |date=2012-10-23 |title=Opposite Behaviors? Arctic Sea Ice Shrinks, Antarctic Grows |url=https://www.nasa.gov/topics/earth/features/arctic-antarctic-ice.html |access-date=2023-01-24 |website=www.nasa.gov |language=en}}]]

A large portion of the Antarctic coastline has ice shelves attached.{{Cite journal |last1=Bindschadler |first1=R. |last2=Choi |first2=H. |last3=Wichlacz |first3=A. |last4=Bingham |first4=R. |last5=Bohlander |first5=J. |last6=Brunt |first6=K. |last7=Corr |first7=H. |last8=Drews |first8=R. |last9=Fricker |first9=H. |date=2011-07-18 |title=Getting around Antarctica: new high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic ice sheet created for the International Polar Year |journal=The Cryosphere |volume=5 |issue=3 |pages=569–588 |bibcode=2011TCry....5..569B |doi=10.5194/tc-5-569-2011 |issn=1994-0424 |s2cid=52888670 |doi-access=free |hdl-access=free |hdl=2060/20120010397}} Their aggregate area is over {{Convert|1,550,000|km2|sqmi|abbr=off|sp=us}}.{{Cite journal |last1=Depoorter |first1=M. A. |last2=Bamber |first2=J. L. |last3=Griggs |first3=J. A. |last4=Lenaerts |first4=J. T. M. |last5=Ligtenberg |first5=S. R. M. |last6=van den Broeke |first6=M. R. |last7=Moholdt |first7=G. |date=2013-10-03 |title=Calving fluxes and basal melt rates of Antarctic ice shelves |journal=Nature |language=en |volume=502 |issue=7469 |pages=89–92 |bibcode=2013Natur.502...89D |doi=10.1038/nature12567 |issn=0028-0836 |pmid=24037377 |s2cid=4462940}}

It has been found that of all the ice shelves on Earth, nearly all of them are in Antarctica.IPCC, 2021: Annex VII: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Glossary] [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. In [https://www.ipcc.ch/report/ar6/wg1/ 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.{{Rp|page=2234}}

In steady state, about half of Antarctica's ice shelf mass is lost to basal melt and half is lost to calving, but the relative importance of each process varies significantly between ice shelves.{{cite journal |last1=Rignot |first1=E. |last2=Jacobs |first2=S. |last3=Mouginot |first3=J. |last4=Scheuchl |first4=B. |date=19 July 2013 |title=Ice-Shelf Melting Around Antarctica |url=https://escholarship.org/uc/item/0jm230gv |journal=Science |volume=341 |issue=6143 |pages=266–270 |bibcode=2013Sci...341..266R |doi=10.1126/science.1235798 |pmid=23765278 |s2cid=206548095 |doi-access=free}}{{cite journal |last1=Depoorter |first1=M. A. |last2=Bamber |first2=J. L. |last3=Griggs |first3=J. A. |last4=Lenaerts |first4=J. T. M. |last5=Ligtenberg |first5=S. R. M. |last6=van den Broeke |first6=M. R. |last7=Moholdt |first7=G. |date=3 October 2013 |title=Calving fluxes and basal melt rates of Antarctic ice shelves |journal=Nature |volume=502 |issue=7469 |pages=89–92 |bibcode=2013Natur.502...89D |doi=10.1038/nature12567 |pmid=24037377 |s2cid=4462940}} In recent decades, Antarctica's ice shelves have been out of balance, as they have lost more mass to basal melt and calving than has been replenished by the influx of new ice and snow.{{cite journal |last1=Greene |first1=Chad A. |last2=Gardner |first2=Alex S. |last3=Schlegel |first3=Nicole-Jeanne |last4=Fraser |first4=Alexander D. |date=10 August 2022 |title=Antarctic calving loss rivals ice-shelf thinning |journal=Nature |volume=609 |issue=7929 |pages=948–953 |bibcode=2022Natur.609..948G |doi=10.1038/s41586-022-05037-w |pmid=35948639 |s2cid=251495070}}

==Ross Ice Shelf==

File:WhalesBayIceShelf.jpg: "The mystic Barrier" at Bay of Whales. Note humans for size comparison (dark spots next to the large chunk of sea ice at left image border). ]]

==Filchner–Ronne Ice Shelf==

{{excerpt|Filchner–Ronne Ice Shelf#Description|paragraphs=1|file=no}}

= Arctic =

== Canada ==

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, Ward Hunt Ice Shelf, Milne Ice Shelf and Smith Ice Shelf. The M'Clintock Ice Shelf broke up from 1963 to 1966; the Ayles Ice Shelf broke up in 2005; and the Markham Ice Shelf broke up in 2008. The remaining ice shelves have also lost a significant amount of their area over time, with the Milne Ice Shelf being the last to be affected, with it breaking off in August 2020.

== Russia ==

The Matusevich Ice Shelf was a {{Convert|222|km2|sqmi|abbr=off|sp=us}} ice shelf located in Severnaya Zemlya being fed by some of the largest ice caps on October Revolution Island, the Karpinsky Ice Cap to the south and the Rusanov Ice Cap to the north.Mark Nuttall, Encyclopedia of the Arctic, p. 1887 In 2012 it ceased to exist.{{Cite journal|last1=Willis|first1=Michael J.|last2=Melkonian|first2=Andrew K.|last3=Pritchard|first3=Matthew E.|date=2015-10-01|title=Outlet glacier response to the 2012 collapse of the Matusevich Ice Shelf, Severnaya Zemlya, Russian Arctic|journal=Journal of Geophysical Research: Earth Surface|language=en|volume=120|issue=10|pages=2015JF003544|doi=10.1002/2015JF003544|issn=2169-9011|bibcode=2015JGRF..120.2040W|doi-access=free}}

Disruption due to climate change

Image:Antarctic shelf ice hg.png

Image:Glacier-ice shelf interactions.svg

In the last several decades, glaciologists have observed consistent decreases in ice shelf extent through melt, calving, and complete disintegration of some shelves. Well studied examples include disruptions of the Thwaites Ice Shelf, Larsen Ice Shelf, Filchner–Ronne Ice Shelf (all three in the Antarctic) and the disruption of the Ellesmere Ice Shelf in the Arctic.

The effects of climate change are visible in the changes to the cryosphere, such as reduction in sea ice and ice sheets, and disruption of ice shelves.

=Disruption of Thwaites Ice Shelf=

File:A_close_look_at_the_shelf_(8093672443).jpg (Antarctica)]]

=Disruption of Larsen Ice Shelf=

Two sections of Antarctica's Larsen Ice Shelf broke apart into hundreds of unusually small fragments (hundreds of meters wide or less) in 1995 and 2002, Larsen C calved a huge ice island in 2017.{{Cite news |last=Kropshofer |first=Katharina |date=2017-10-09 |title=Scientists hope damage to Larsen C ice shelf will reveal ecosystems |language=en-GB |work=The Guardian |url=https://www.theguardian.com/environment/2017/oct/09/scientists-hope-damage-to-larsen-c-ice-shelf-will-reveal-ecosystems |access-date=2018-01-05 |issn=0261-3077}}

==Disruption of Larsen B Ice Shelf==

=Disruption of Filchner–Ronne Ice Shelf=

= Other ice shelves in Antarctica =

Wordie Ice Shelf has gone from an area of {{convert|1500|km2|sqmi|abbr=on}} in 1950 to {{convert|1400|km2|sqmi|abbr=on}} in 2000.{{cite journal |author1=A. J. Cook |author2=D. G. Vaughan |name-list-style=amp |year=2009 |title=Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years |url=http://dro.dur.ac.uk/20037/1/20037.pdf |journal=The Cryosphere Discussions |volume=3 |issue=2 |pages=579–630 |bibcode=2010TCry....4...77C |doi=10.5194/tcd-3-579-2009 |doi-access=free}}
Prince Gustav Ice Shelf has gone from an area of {{convert|1600|km2|sqmi|abbr=on}} to {{convert|1100|km2|sqmi|abbr=on}} in 2008. After their loss the reduced buttressing of feeder glaciers has allowed the expected speed-up of inland ice masses after shelf ice break-up.{{cite journal |last1=Rignot |first1=E. |last2=Casassa |first2=G. |last3=Gogineni |first3=P. |last4=Krabill |first4=W. |last5=Rivera |first5=A. |last6=Thomas |first6=R. |year=2004 |title=Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf |journal=Geophysical Research Letters |volume=31 |issue=18 |pages=L18401 |bibcode=2004GeoRL..3118401R |doi=10.1029/2004GL020697 |doi-access=free}}
The Ross Ice Shelf is the largest ice shelf of Antarctica (an area of roughly {{convert|487000|sqkm}} and about {{convert|800|km}} across: about the size of France).{{Cite web |title=Antarctic Hazards – British Antarctic Survey |url=http://www.antarctica.ac.uk/about_antarctica/teacher_resources/information/faqs/hazards.php |url-status=dead |archive-url=https://web.archive.org/web/20150711062739/http://www.antarctica.ac.uk/about_antarctica/teacher_resources/information/faqs/hazards.php |archive-date=2015-07-11 |access-date=2015-05-22}}
Wilkins Ice Shelf is another ice shelf that has suffered substantial retreat. The ice shelf had an area of {{convert|16000|km2|sqmi|abbr=on}} in 1998 when {{convert|1000|km2|sqmi|abbr=on}} was lost that year.{{cite journal |author1=M. Humbert, A. Braun |author2=A. Moll |name-list-style=amp |year=2009 |title=Changes of Wilkins Ice Shelf over the past 15 years and inferences on its stability |journal=The Cryosphere |volume=3 |issue=1 |pages=41–56 |bibcode=2009TCry....3...41B |doi=10.5194/tc-3-41-2009 |doi-access=free}} In 2007 and 2008 significant rifting developed and led to the loss of another {{convert|1400|km2|sqmi|abbr=on}} of area and some of the calving occurred in the Austral winter. The calving seemed to have resulted from preconditioning such as thinning, possibly due to basal melt, as surface melt was not as evident, leading to a reduction in the strength of the pinning point connections. The thinner ice then experienced spreading rifts and breakup.{{cite web |author=Mauri S. Pelto |date=12 June 2008 |title=Ice Shelf Instability |url=http://www.realclimate.org/index.php/archives/2008/06/ice-shelf-instability/langswitch_lang/tk |access-date=August 7, 2016}} This period culminated in the collapse of an ice bridge connecting the main ice shelf to Charcot Island leading to the loss of an additional {{convert|700|km2|sqmi|abbr=on}} between February and June 2009.{{cite news |author=ESA |date=June 13, 2009 |title=Satellite imagery shows fragile Wilkins Ice Shelf destabilised |url=http://www.esa.int/esaEO/SEMRAVANJTF_index_0.html |publisher=European Space Agency}}

=Disruption of Ellesmere Ice Shelf (Arctic)=

The Ellesmere ice shelf was reduced by 90% 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 kilometres) of ice calved from the Milne and Ayles ice shelves between 1959 and 1974.Jeffries, Martin O.[http://pubs.aina.ucalgary.ca/arctic/Arctic39-1-15.pdf Ice Island Calvings and Ice Shelf Changes, Milne Ice Shelf and Ayles Ice Shelf, Ellesmere Island, N.W.T.] {{Webarchive|url=https://web.archive.org/web/20190928113808/http://pubs.aina.ucalgary.ca/arctic/Arctic39-1-15.pdf|date=2019-09-28}}. Arctic 39 (1) (March 1986) The Ayles Ice Shelf calved entirely on August 13, 2005. The Ward Hunt Ice Shelf, the largest remaining section of thick (>{{Convert|10|m|ft|abbr=off|sp=us}}) landfast sea ice along the northern coastline of Ellesmere Island, lost {{Convert|600|km2|sqmi|abbr=off|sp=us}} of ice in a massive calving in 1961–1962.Hattersley-Smith, G. The Ward Hunt Ice Shelf: recent changes of the ice front. Journal of Glaciology 4:415–424. 1963. It further decreased by 27% in thickness ({{Convert|13|m|ft|abbr=off|sp=us}}) between 1967 and 1999.Vincent, W.F., J.A.E. Gibson, M.O. Jeffries. [http://www.cen.ulaval.ca/warwickvincent/PDFfiles/149.pdf Ice-shelf collapse, climate change, and habitat loss in the Canadian high Arctic]. Polar Record 37 (201): 133–142 (2001) In the summer of 2002, the Ward Ice Shelf experienced another major breakup,{{cite web |author=NASA Earth Observatory |date=2004-01-20 |title=Breakup of the Ward Hunt Ice Shelf |url=http://earthobservatory.nasa.gov/Study/wardhunt/}} and other instances of note happened in 2008 and 2010 as well.{{Cite web |last=Canada |first=Environment and Climate Change |date=2010-12-17 |title=Ward Hunt ice shelf calving – Canada.ca |url=https://www.canada.ca/en/environment-climate-change/services/ice-forecasts-observations/latest-conditions/educational-resources/shelves/ward-hunt-calving.html |access-date=2018-01-05 |website=www.canada.ca |language=en}} The last remnant to remain mostly intact, the Milne Ice Shelf, also ultimately experienced a major breakup at the end of July 2020, losing over 40% of its area.{{Cite news |date=2020-08-06 |title=Canada's last fully intact Arctic ice shelf collapses |language=en |work=Reuters |url=https://www.reuters.com/article/us-climate-change-canada-idUSKCN2523JH |access-date=2020-08-07}}{{excerpt|Ellesmere Ice Shelf}}

References

External links

[http://www.antarctica.gov.au/about-antarctica/environment/icebergs-and-ice/ice-shelves Further information from the Australian Antarctic Division] {{Webarchive|url=https://web.archive.org/web/20170821073319/http://www.antarctica.gov.au/about-antarctica/environment/icebergs-and-ice/ice-shelves |date=2017-08-21 }}

Shelf

Category:Snow or ice weather phenomena

Category:Water ice