Larsen Ice Shelf

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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' S 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 of 1995. The Larsen B ice shelf disintegrated in February of 2002. The Larsen C ice shelf appears to be stable. Scientists predict that the Larsen C ice shelf has at least three more years until it disintegrates. If global warming continues at the rate it is now, the Larsen C ice shelf has most likely one year until it is destroyed.^{[citation needed]}

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 1940's, which is a consequence of global warming.^[2]

[edit] 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 2002-01-31–2002-03-07 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 state of Rhode Island disappeared in a single season.^[3] Larsen B was stable for up to 12,000 years, essentially the entire Holocene period since the last ice age, according to Queen's University researchers.^[4] 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."^[5] 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.^[6][7] 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, ^[8]

Although the remaining Larsen C region, which is the furthest south, appears to be relatively stable for now,^[9] it is anticipated that it too may break up sometime in the coming decade.^[10] If disintegration should occur with this last major sector, which is larger in size than the 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 Texas."^[11]

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.^[4] 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.^[12]

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

[edit] Popular culture

The Larsen B Ice Shelf is the subject of a song by the band British Sea Power. "Oh Larsen B" appears on their 2005 album Open Season, and contains the lyric "my favourite foremost coastal Antarctic shelf ... oh Larsen B, oh won't you fall on me ... desalinate the barren sea". This has often been mis-quoted as "desalinate the Barents Sea" which has caused confusion as the Barents Sea is in the Arctic.

The ice shelf has also been made the subject of a song by instrumental metal/drone band 5ive. The song, "Sleep For The Larsen B Shelf," appears on their The Telestic Disfracture album.

Larsen B Ice Shelf appeared also in the 2004 film The Day After Tomorrow where a huge chunk of ice fell off as Hall proclaimed 'the last chunk of ice that fell off was about the size of Rhode Island'. This opening sequence paves the way for the events to follow in the rest of the film.

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.

[edit] See also

• List of glaciers and ice shelves in Antarctica

[edit] References

[edit] External links

Wikinews has related news:

Larson B ice-shelf collapse reveals exotic organisms isolated for 10,000 years

• Antarctic Ice Shelves and Icebergs, U.S. National Snow and Ice Data Center
• Instituto Antártico Argentino
• Animation of Larsen B breakup, 31 January to 7 March 2002

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