Larsen Ice Shelf#Larsen B

File:Antarctica map indicating Antarctic Peninsula.JPG]]

The collapse of Larsen B has revealed a thriving chemotrophic ecosystem 800 m (half a mile) below the sea. The discovery was accidental. U.S. Antarctic Program scientists were in the north-western Weddell Sea investigating the sediment record in a deep glacial trough of roughly {{convert|1000000|km2}} (twice the size of Texas or France). Methane and hydrogen sulfide associated with cold seeps is suspected as the source of the chemical energy powering the ecosystem. The area had been protected by the overlying ice shelf from debris and sediment which was seen to be building up on the white microbial mats after the breakup of the ice shelf. Clams were observed clustered about the vents.{{cite journal |last1=Domack |first1=Eugene |last2=Ishman |first2=Scott |last3=Leventer |first3=Amy |last4=Sylva |first4=Sean |last5=Willmott |first5=Veronica |last6=Huber |first6=Bruce| author-link1=Eugene Domack |date=19 July 2005 |title=A Chemotrophic Ecosystem Found Beneath Antarctic Ice Shelf |journal=Eos, Transactions American Geophysical Union |doi=10.1029/2005EO290001 |bibcode=2005EOSTr..86..269D |volume=86 |issue=29 |pages=269 |url=http://onlinelibrary.wiley.com/store/10.1029/2005EO290001/asset/eost15171.pdf;jsessionid=EB172B44BB814DEDF0438E4781B86659.f03t03?v=1&t=iuk8ugy6&s=6105a95bdf03ba0d287d63cd03a7666c8e3011b9 |access-date=20 October 2016|doi-access=free }}

File:Antarctic shelf ice hg.png

The former Larsen A region, which was the farthest north and was just outside the Antarctic Circle, had previously broken up in the middle of the present interglacial and reformed only about 4,000 years ago. The former Larsen B, by contrast, had been stable for at least 10,000 years. The ice of the shelf is renewed on a much shorter time-scale and the oldest ice on the current shelf dates from only two hundred years ago. The speed of Crane Glacier increased threefold after the collapse of the Larsen B, likely due to the removal of a buttressing effect of the ice shelf.{{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 |doi=10.1029/2004GL020697 |bibcode=2004GeoRL..3118401R|volume=31 |issue=18 |pages=L18401 |url=http://web.ist.utl.pt/~nuno.j.aniceto/documents/stuff/documents/RignotetalGRLPeninsulaAccel.pdf |access-date=22 October 2016|doi-access=free }} Data collected in 2007 by an international team of investigators through satellite-based radar measurements suggests that the overall ice-sheet mass balance in Antarctica is increasingly negative.Perlman, David (2008) "Antarctic Glaciers Melting More Quickly" San Francisco Chronicle (26 January) p. A2, [http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/01/26/MN50UM20C.DTL online]

File:Larsen B Collapse.jpg.]]

The Larsen disintegration events were unusual by past standards. Typically, ice shelves lose mass by iceberg calving and by melting at their upper and lower surfaces. The disintegration events were linked by The Independent newspaper in 2005 to ongoing climate warming in the Antarctic Peninsula, about 0.5˚C (0.9˚F) per decade since the late 1940s.Connor, Steve (2005) "Ice shelf collapse was biggest for 10,000 years since Ice Age" The Independent, London (4 August), [https://www.independent.co.uk/news/science/ice-shelf-collapse-was-biggest-for-10000-years-303492.html online] According to a paper published in Journal of Climate in 2006, the peninsula at Faraday station warmed by 2.94˚C (5.3˚F) from 1951 to 2004, much faster than Antarctica as a whole and faster than the global trend; anthropogenic global warming causes this localized warming through a strengthening of the winds circling the Antarctic.{{Cite journal | doi=10.1175/JCLI3844.1|title = The Impact of a Changing Southern Hemisphere Annular Mode on Antarctic Peninsula Summer Temperatures| journal=Journal of Climate| volume=19| issue=20| pages=5388–5404|year = 2006|last1 = Marshall|first1 = Gareth J.| last2=Orr| first2=Andrew| last3=Van Lipzig| first3=Nicole P. M.| last4=King| first4=John C.|bibcode = 2006JCli...19.5388M| url=http://www.vliz.be/imisdocs/publications/283801.pdf}}

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The Larsen A ice shelf disintegrated in January 1995. It was an ice shelf near the Prince Gustav Ice Shelf, extending from Cape Longing to Robertson Island, and merged with Larsen B at Seal Nunataks. It was relatively stable and around 4000 km^2 from 1961, until around the 1980s, when large calving resulted in eventual collapse.

{{cite journal |last=Fox |first=Douglas |title=Witness to an Antarctic Meltdown |journal=Scientific American |doi=10.1038/scientificamerican0712-54 |pmid=22779273 |volume=307 |issue=1 |pages=54–61 |bibcode=2012SciAm.307a..54F |year=2012 }}

File:Larsen B collapse.jpg

From 31 January 2002 to March 2002 the Larsen B sector partially collapsed and parts broke up, {{convert|3250|km2|abbr=on}} of ice {{convert|220|m|abbr=on}} thick, an area comparable to the US state of Rhode Island.{{cite web |last=Hulbe |first=Christina |year=2002 |title=Larsen Ice Shelf 2002, warmest summer on record leads to disintegration |website=Portland State University |url=http://web.pdx.edu/~chulbe/science/Larsen/larsen2002.html}} In 2015, a study concluded that the remaining Larsen B ice-shelf would disintegrate by 2020, based on observations of faster flow and rapid thinning of glaciers in the area.{{cite press release |publisher=NASA |date=14 May 2015 |title=NASA Study Shows Antarctica's Larsen B Ice Shelf Nearing Its Final Act |url=http://www.nasa.gov/press-release/nasa-study-shows-antarctica-s-larsen-b-ice-shelf-nearing-its-final-act}}

Larsen B was stable for at least 10,000 years, essentially the entire Holocene period since the last glacial period.{{cite press release |date=3 August 2005 |title=Ice Shelf disintegration threatens environment, Queen's study |publisher=Queens University |location=Kingston, Ontario |url=http://www.eurekalert.org/pub_releases/2005-08/qu-isd080305.php |via=American Association for the Advancement of Science's Eurekalert}} By contrast, Larsen A was absent for a significant part of that period, reforming about 4,000 years ago.

Despite its great age, the Larsen B was clearly in trouble at the time of the collapse. With warm currents eating away the underside of the shelf, it had become a "hotspot of global warming".{{cite book |last=Pearce |first=Fred |author-link=Fred Pearce |year=2006 |title=The Last Generation: How Nature Will Take Her Revenge for Climate Change |publisher=Eden Project Books |page=92 |isbn=978-1-903919-87-3}} It broke over a period of three weeks or less, with a factor in this fast break-up being the powerful effects of water; ponds of meltwater formed on the surface during the near 24 hours of daylight in the summertime, flowed down into cracks and, acting like a multitude of wedges, levered the shelf apart.{{cite web |title=Larsen B Ice Shelf Collapses in Antarctica |website=National Snow and Ice Data Center |url=https://nsidc.org/news/newsroom/larsen_B/2002.html |date=18 March 2002 |access-date=2017-07-12 |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 }}{{cite web |url=http://www.colorado.edu/today/2001/01/15/antarctic-ice-shelf-collapse-triggered-warmer-summers |title=Antarctic Ice Shelf Collapse Triggered By Warmer Summers |publisher=Office of News Services, University of Colorado at Boulder |date=16 January 2001 |access-date=2017-07-12}} Other likely factors in the break-up were the higher ocean temperatures and the decline of the ice of the peninsula.{{cite web |date=7 February 2008 |title=Experts challenge ice shelf claim |work=Two scientists have claimed that climate change was not the only cause of the collapse of a 500bn tonne ice shelf in Antarctica six years ago |publisher=BBC News |url=http://news.bbc.co.uk/2/hi/uk_news/wales/mid_/7231372.stm |access-date=21 October 2016}}

In the austral winter of 2011, a large expanse of sea ice formed over the embayment that was once covered by the land-fast shelf of fresh-water glacial ice of Larsen B. This enormous ice pack persisted through January 2022 when it suddenly broke-up over the course of a few days, "taking with it a Philadelphia-sized piece of the Scar Inlet Ice Shelf," according to NASA scientists examining images from the Terra and Aqua satellites.{{cite web |url=https://earthobservatory.nasa.gov/images/149410/larsen-b-embayment-breaks-up |title=Larsen B Embayment Breaks Up |last=Hansen |first=Kathryn |last2=Stevens |first2=Joshua |date=January 26, 2022 |website=NASA Earth Observatory |publisher=National Aeronautics and Space Administration |access-date=February 6, 2022}}

{{See also|Iceberg A-68}}

File:LarsenC photo 2016315 lrg.jpg

File:Glacier-ice shelf interactions.svg

File:Iceberg A-68 - July 20 2017.jpg

{{As of|July 2017}}, Larsen C was the fourth largest ice shelf in Antarctica, with an area of about {{convert|44,200|km2|abbr=on}}.{{cite web |title=Growing Crack in Antarctica's Larsen C Ice Shelf Spotted by NASA's MISR |website = Jet Propulsion Laboratory|url=http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA20894}}

Satellite radar altimeter measurements show that between 1992 and 2001, the Larsen Ice Shelf thinned by up to 0.27 ± 0.11 meters per year.{{Cite journal|last1=Shepherd|first1=Andrew|last2=Wingham|first2=Duncan|last3=Payne|first3=Tony|last4=Skvarca|first4=Pedro|date=2003-10-31|title=Larsen Ice Shelf Has Progressively Thinned|journal=Science|language=en|volume=302|issue=5646|pages=856–859|doi=10.1126/science.1089768|issn=0036-8075|pmid=14593176|bibcode=2003Sci...302..856S|s2cid=7034012}} In 2004, a report concluded that although the remaining Larsen C region appeared to be relatively stable,Riedl C, Rott H, Rack W (2004) "Recent Variations of Larsen Ice Shelf, Antarctic Peninsula, Observed by Envisat" Proceedings of the 2004 Envisat & ERS Symposium, Salzburg, Austria, [http://epic.awi.de/14515/1/Rie2004b.pdf online] continued warming could lead to its breakup within the following decade.Rignot, Eric (2007) "Mass Balance and Ice Dynamics of Antarctic Peninsula Glaciers for IPY2007-2008" Proposal #359, International Polar Year Expression of Intent.

The breakaway process for the iceberg had begun by mid-2016.{{cite web |url=http://www.projectmidas.org/blog/a-growing-rift-in-larsen-c/ |title=A growing rift on Larsen C |author1=Adrian Luckman |author2=Daniela Jansen |author3=Martin O'Leary |author4=the MIDAS team |date=18 August 2016 |website=projectmidas.org |access-date=21 October 2016 }}{{cite web |url=http://zeenews.india.com/environment/a-massive-rift-is-threatening-antarctic-larsen-c-ice-shelf-to-collapse_1921544.html |title=A massive rift is threatening Antarctic Larsen C ice shelf to collapse |author=Zee Media Bureau |date=23 August 2016 |website=zeenews.india.com |access-date=21 October 2016 |quote=Media report on Project MIDAS}} On 10 November 2016 scientists photographed the growing rift running along the Larsen C ice shelf,{{Cite web|url=https://www.nasa.gov/image-feature/rift-in-antarcticas-larsen-c-ice-shelf|title=Rift in Antarctica's Larsen C Ice Shelf|date=13 December 2016|editor-last=Loff|editor-first=Sarah|publisher=NASA|others=John Sonntag (image credit)|access-date=5 January 2017}} showing it running about {{Convert|110|km}} long with a width of more than {{Convert|91|m|abbr=on}}, and a depth of {{convert|500|m|abbr=on}}. By December 2016, the rift had extended another {{Convert|21|km|abbr=on}} to the point where only {{Convert|20|km|abbr=on}} of unbroken ice remained and calving was considered to be a certainty in 2017.{{Cite news|url=https://www.bbc.com/news/science-environment-38522954|title=Huge Antarctic iceberg poised to break away|last=McGrath|first=Matt|date=5 January 2017|publisher=BBC|department=Science & Environment|access-date=5 January 2017|via=BBC.com}} This was predicted to cause the calving of between nine and twelve percent of the ice shelf, {{Convert|6000|km2|abbr=on}}, an area greater than the US state of Delaware, or twice the size of Luxembourg.{{cite news|url=https://www.theguardian.com/world/2017/jul/12/giant-antarctic-iceberg-breaks-free-of-larsen-c-ice-shelf|title=Iceberg twice size of Luxembourg breaks off Antarctic ice shelf|publisher=Guardian|language=en|author=Nicola Davis|date=12 July 2017|access-date=13 July 2017}} The calved fragment was predicted to be {{Convert|350|m|ft|abbr=on}} thick and to have an area of about {{Convert|5000|km2|abbr=on}}. The resulting iceberg was predicted to be among the largest icebergs ever recorded, unless it would break into multiple pieces.

On 1 May 2017 members of MIDAS reported that satellite images showed a new crack, around {{convert|15|km|0|abbr=on}} long, branching off the main crack approximately {{convert|10|km|0|abbr=on}} behind the previous tip, heading toward the ice front.{{cite web|url=https://www.usatoday.com/story/tech/sciencefair/2017/05/02/new-crack-forms-antarctic-ice-shelf/101195464/|title=Huge Antarctic ice shelf crack now has second branch|website=USA Today}} Scientists with Swansea University in the UK say the crack lengthened {{convert|18|km|0|abbr=on}} from 25 May to 31 May, and that less than {{convert|13|km|0|abbr=on}} of ice is all that prevents the birth of an enormous iceberg. "The rift tip appears also to have turned significantly towards the ice front, indicating that the time of calving is probably very close," Adrian Luckman and Martin O'Leary wrote on Wednesday in a blog post for the Impact of Melt on Ice Shelf Dynamics and Stability project, or MIDAS. "There appears to be very little to prevent the iceberg from breaking away completely." The larger swath of the Larsen C ice shelf that sat behind the calved iceberg "will be less stable than it was prior to the rift" and may rapidly disintegrate in the same manner as Larsen B did in 2002.{{Cite news|url=http://www.businessinsider.com/antarctica-giant-iceberg-breaking-off-2017-6|title=A giant crack in Antarctic ice is 'days or weeks' from breaking off a Delaware-size iceberg|work=Business Insider|access-date=2 June 2017|language=en}}

In June 2017 the speed of the imminent Larsen C iceberg accelerated, with the eastern end moving at {{convert|10|m|feet}} per day away from the main shelf.{{cite web|last1=O'Leary|first1=Martin|last2=Luckman|first2=Adrian|last3=Project MIDAS|title=Larsen C iceberg accelerates ahead of calving|url=http://www.projectmidas.org/blog/berg-acceleration/|website=Project MIDAS|access-date=1 July 2017}} As discussed by the Project MIDAS researchers on their site: "In another sign that the iceberg calving is imminent, the soon-to-be-iceberg part of Larsen C ice shelf has tripled in speed to more than 10 meters per day between 24 and 27 June 2017. The iceberg remains attached to the ice shelf, but its outer end is moving at the highest speed ever recorded on this ice shelf."{{Cite web|url=https://cleantechnica.com/2017/06/30/larsen-c-ice-shelf-rift-approaching-end-outer-edge-moving-away-ice-shelf-speed-33-feet-per-day/|title=Larsen C Ice Shelf Rift Approaching Its End, Outer Edge Moving Away From Ice Shelf At Speed Of 33 Feet Per Day|website=CleanTechnica|date=30 June 2017|access-date=2017-07-01}}

On 7 July the Project MIDAS blog report stated: "The latest data from 6th July reveal that, in a release of built-up stresses, the rift branched several times. Using data from ESA's Sentinel-1 satellites, we can see that there are multiple rift tips now within 5 km (3.10 miles) of the ice edge. We expect that these rifts will lead to the formation of several smaller icebergs."{{Cite web|url=http://www.projectmidas.org/blog/multiple-branches/|title=Larsen C rift branches as it comes within 5 km of calving|website=Project MIDAS|access-date=7 July 2017}}

On 12 July 2017, Project MIDAS announced that a large, {{convert|5800|sqkm|mi2|adj=on|sigfig=2}} portion of Larsen C had broken from the main ice shelf at some point between 10 and 12 July.{{Cite news|url=https://www.bbc.com/news/science-environment-40321674|title=Giant iceberg splits from Antarctic|publisher=BBC|date=12 July 2017}} The iceberg, designated A-68, weighs more than a trillion tons{{Cite news|url=http://www.cnn.com/2017/07/12/world/larsen-c-antarctica/index.html|title=Massive iceberg breaks away from Antarctica|publisher=CNN|date=12 July 2017}}{{cite web|title=Larsen C calves trillion ton iceberg|url=http://www.projectmidas.org/blog/calving/|publisher=Project MIDAS|access-date=12 July 2017|date=12 July 2017}} and is more than {{convert|200|m|abbr=on|sigfig=1}} thick.{{cite news|url=https://www.bbc.co.uk/news/science-environment-40321674|title=Giant iceberg splits from Antarctic|date=12 July 2017|work=BBC|last1=Amos|first1=Jonathan|access-date=12 July 2017}}{{Cite web|url=http://www.projectmidas.org/blog/calving/|title=Larsen C calves trillion ton iceberg|last=MIDAS|first=Project|website=Project MIDAS|access-date=2017-07-12}}

Project MIDAS updated their blog information on 19 July 2017 regarding Larsen C by revealing that a possible new rift appeared to be extending northwards from the point where A-68 had broken off in mid-July. The project researchers felt this questionable new rift might turn towards the shelf edge, compounding the risk that it would "continue on to Bawden ice rise" which is considered "a crucial point of stabilization for Larsen C Ice Shelf."{{Cite web|url=http://www.projectmidas.org/blog/larsen-c-responds/|title=Larsen C responds to the calving of A68|last=MIDAS|first=Project|website=Project MIDAS|access-date=2017-07-20}}

As is true of all floating ice shelves, A68's departure from Antarctica had no immediate effect on global sea levels. However, a number of glaciers discharge onto the shelf from the land behind it, and they may now flow faster due to reduced support from the ice shelf. If all the ice that the Larsen C shelf currently holds back were to enter the sea, global waters would rise by an estimated {{convert|10|cm|abbr=on|sigfig=1}}.{{cite web |date=6 January 2017 |title=Huge Antarctic iceberg poised to break away |publisher=BBC News |url=https://www.bbc.co.uk/news/science-environment-38522954 |access-date=6 January 2017}}

The Larsen D Ice Shelf is between Smith Peninsula in the south and Gipps Ice Rise. It is considered to be generally stable. Over roughly the past fifty years it has advanced (expanded) whereas comparable George VI, Bach, Stange, and Larsen C ice shelves have retreated (to a much greater net extent). The most recent survey of Larsen D measured it at 22,600 km². There is fast ice along the entire front. This makes it difficult to interpret the ice front because the semi-permanent sea ice varies in thickness and may be nearly indistinguishable from shelf ice.[http://www.the-cryosphere-discuss.net/3/579/2009/tcd-3-579-2009.pdf Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere Discussions. 3 pp579-630.]

File:Antarctic Peninsula, the Larsen Ice Shelf, and the sea ice covered waters around the region.jpg|Clear view of the Antarctic Peninsula, the Larsen Ice Shelf, and the sea ice covered waters around the region.

File:Larsen B March 2013.jpg|Larsen B area in March 2013

File:LarsenC-detail photo 2016315 lrg.jpg|2016 rift in Larsen C, detail

File:Larsen c crack nasa worldview 20170712.jpg|Imagery from NASA's Aqua MODIS showing the complete break of the ice shelf as of 12 July 2017

File:Larsen C breaks.jpg|Radar imagery from ESA's Sentinel-1B taken on 12 July 2017, showing the complete break

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{{Reflist}}

{{Wikinews|Larson B ice-shelf collapse reveals exotic organisms isolated for 10,000 years}}

• {{Commonscatinline}}
• [http://earthobservatory.nasa.gov/IOTD/view.php?id=2288 "Break up of the Larsen Ice Shelf, Antarctica"], NASA Earth Observatory.
• [http://purl.access.gpo.gov/GPO/LPS112067 Coastal-change and Glaciological Map of the Larsen Ice Shelf Area, Antarctica, 1940-2005 ] United States Geological Survey
• [http://www.swansea.ac.uk/media-centre/latest-research/antarcticiceriftclosetocalvingaftergrowing17kmin6days.php Antarctic ice rift close to calving, after growing 17km in 6 days] {{Webarchive|url=https://web.archive.org/web/20170829200015/http://www.swansea.ac.uk/media-centre/latest-research/antarcticiceriftclosetocalvingaftergrowing17kmin6days.php |date=29 August 2017 }} (Swansea University, Project Midas - June 2017)

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