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Larsen A and Larsen B iceshelves marked in red

The Larsen Ice Shelf is a long, fringing ice shelf in the northwest part of the Weddell Sea, extending along the east coast of Antarctic Peninsula from Cape Longing to the area just southward of Hearst Island. Named for Captain Carl Anton Larsen, the master of the Norwegian whaling vessel Jason, who sailed along the ice front as far as 68°10' South during December 1893.[1]

In finer detail, the Larsen Ice Shelf is a series of three shelves that occupy (or occupied) distinct embayments along the coast. From north to south, the three segments are called Larsen A (the smallest), Larsen B, and Larsen C (the largest) by researchers who work in the area. The Larsen A ice shelf disintegrated in January 1995. The Larsen B ice shelf disintegrated in February 2002. The Larsen C ice shelf appears to be stable for the time being, though scientists predict that, if localized warming continues at its current rate, the shelf could disintegrate at some point within the foreseeable future.[2]

The Larsen disintegration events were unusual. Typically, ice shelves lose mass by iceberg calving and by melting at their upper and lower surfaces. The disintegration events are linked to the ongoing climate warming in the Antarctic Peninsula, about 0.5 °C per decade since the late 1940s. which is a consequence of localized warming of the Antarctic peninsula.[3] This localized warming is possibly caused by anthropogenic global warming, according to some scientists through strengthening of the Antarctic annular winds.[4]

Contents

Larsen A, B & C sectors

The collapse of Larsen B, showing the diminishing extent of the shelf from 1998 to 2002
Glacier-ice shelf interactions

During 31 January 2002–7 March 2002 the Larsen B sector collapsed and broke up, 3,250 km² of ice 220 m thick disintegrated, meaning an ice shelf covering an area comparable in size to the US state of Rhode Island disappeared in a single season.[5] Larsen B was stable for up to 12,000 years, essentially the entire Holocene period since the last glacial period, according to Queen's University researchers.[6] By contrast, Larsen A "was absent for a significant part of that period and reformed beginning about 4,000 years ago," according to the study.

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."[7] What especially surprised glaciologists was the speed of the breakup, which was a mere three weeks (or less). A factor they had not anticipated was the powerful effects of liquid water; ponds of meltwater formed on the surface during the near 24 hours of daylight in the summertime, then the water flowed down into cracks and, acting like a multitude of wedges, levered the shelf apart, almost in one fell swoop.[8][9] Global increase in air temperature was not the only factor contributing to the break according to Ted Scambos, of the University of Colorado's national snow and ice data centre.

"It's likely that melting from higher ocean temperatures, or even a gradual decline in the ice mass of the peninsula over the centuries, was pushing the Larsen to the brink"
Ted Scambos, [10]

Although the remaining Larsen C region, which is the furthest south, appears to be relatively stable for now,[11] continued warming could lead to its breakup within the next decade.[12] If disintegration should occur with this last major sector, which is larger in size than the US states of New Hampshire and Vermont combined—then the enormous Larsen Ice Shelf viewed in 1893 by Carl Anton Larsen and his crew aboard the Jason will largely be gone in just over a century after first discovery, which is a mere flash in geologic time.

The collapse of Larsen B has revealed a thriving ecosystem 800 m (half a mile) below the sea. "Despite near freezing and sunless conditions, a community of clams and a thin layer of bacterial mats are flourishing in undersea sediments. [...] The discovery was accidental. U.S. Antarctic Program scientists were in the northwestern Weddell Sea investigating the sediment record in a deep glacial trough twice the size of [the US state of] Texas."[13]

Studies show that in the middle of the present interglacial the former Larsen A region, which was the furthest north and outside the Antarctic Circle, had previously broken up and reformed only about 4,000 years ago, although the former Larsen B had been stable for at least 10,000 years.[6] The maximal ice age on the current shelf dates from only two hundred years ago. The precipitation on the Antarctic Peninsula is on average increasing[citation needed], leading to ice shelves flowing more quickly into the sea and glaciers retreating at a faster pace. Recent data collected by an international team of investigators through satellite-based radar measurements suggests that the overall ice-sheet mass balance in Antarctica is increasingly negative.[14]

An image of the collapsing Larsen B Ice Shelf and a comparison of this to the U.S. state of Rhode Island.

Popular culture

The Larsen B Ice Shelf is the subject of a song by the band Sian Alice Group from their album 59.59. British Sea Power have also written a song entitled "Oh Larsen B", which appears on their 2005 album Open Season. It contains the lyric "You're fractured and cold but your heart is unbroken, my favourite foremost coastal Antarctic shelf ... oh Larsen B, oh you can fall on me ... desalinate the barren sea".

Larsen B Ice Shelf also appears in the opening sequence of the 2004 film The Day After Tomorrow. Its collapse foreshadows events to follow in the rest of the film, and prompts the main character to later proclaim, "Well, the last chunk of ice that broke off was about the size of the state of Rhode Island."

The disintegration of the shelf is referenced in Al Gore's environmental documentary film An Inconvenient Truth as evidence in support of global warming. It is also part of the background story of the book O Sétimo Selo (The Seventh Seal) by Portuguese writer and journalist José Rodrigues dos Santos.

See also

References

  1. ^ U.S. Geological Survey Geographical Names Information System: Larsen Ice Shelf
  2. ^ Larsen C thinning
  3. ^ Connor, Steve (2005) "Ice shelf collapse was biggest for 10,000 years since Ice Age" The Independent, London (Aug 4), online
  4. ^ Marshall et al., "The Impact of a Changing Southern Hemisphere Annular Mode on Antarctic Peninsula Summer Temperatures", Journal of Climate, vol. 19, pp.5388-5404, October 2006.
  5. ^ Hulbe, Christina (2002) "Larsen Ice Shelf 2002, warmest summer on record leads to disintegration" website of Portland State University, online
  6. ^ a b Press Release (2005) "Ice Shelf disintigration threatens environment, Queen's study" Queens University, Kingston, Ontario, online
  7. ^ Pearce, Fred (2006) The Last Generation: How Nature Will Take Her Revenge for Climate Change, Eden Project Books, p. 92
  8. ^ Larsen B Ice Shelf Collapses in Antarctica
  9. ^ Antarctic Ice Shelf Collapse Triggered By Warmer Summers Office of News Services, University of Colorado at Boulder, Jan. 16, 2001
  10. ^ "Experts challenge ice shelf claim". 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.. BBC News. 7 February 2008. http://news.bbc.co.uk/2/hi/uk_news/wales/mid_/7231372.stm. Retrieved 2008-02-07. 
  11. ^ 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, online
  12. ^ Rignot, Eric (2007) "Mass Balance and Ice Dynamics of Antarctic Peninsula Glaciers for IPY2007-2008" Proposal #359, International Polar Year Expression of Intent, online
  13. ^ Carey, Bjorn (2005) "Ice Shelf Collapse Reveals New Undersea World" LiveScience website, online
  14. ^ Perlman, David (2008) "Antarctic Glaciers Melting More Quickly" San Francisco Chronicle (January 26) p. A2, online

External links

Coordinates: 67°30′S 62°30′W / 67.5°S 62.5°W / -67.5; -62.5

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