
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.
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.
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. This localized warming is possibly caused by
anthropogenic global warming, according to some scientists
through strengthening of the Antarctic annular winds.
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. 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. 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." 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.
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.
Although the remaining Larsen C region, which is the furthest
south, appears to be relatively stable for now, continued warming
could lead to its breakup within the next decade. 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
."
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. 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 , 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.
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".
This has often been mis-quoted as
"desalinate the Barents Sea" which has caused confusion as the
Barents
Sea
is in the Arctic.
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
- Larsen C thinning
- Connor, Steve (2005) "Ice shelf collapse was biggest for 10,000
years since Ice Age" The Independent, London (Aug 4),
online
- 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.
- Hulbe, Christina (2002) "Larsen Ice Shelf 2002, warmest summer
on record leads to disintegration" website of Portland State
University, online
- Press Release (2005) "Ice Shelf disintigration threatens
environment, Queen's study" Queens University, Kingston, Ontario,
online
- Pearce, Fred (2006) The Last Generation: How Nature Will
Take Her Revenge for Climate Change, Eden Project Books, p.
92
- Larsen B Ice Shelf Collapses in Antarctica
- Antarctic Ice Shelf Collapse Triggered By Warmer
Summers Office of News Services, University of Colorado at
Boulder, Jan. 16, 2001
- 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
- Rignot, Eric (2007) "Mass Balance and Ice Dynamics of Antarctic
Peninsula Glaciers for IPY2007-2008" Proposal #359, International
Polar Year Expression of Intent, online
- Carey, Bjorn (2005) "Ice Shelf Collapse Reveals New Undersea
World" LiveScience website, online
- Perlman, David (2008) "Antarctic Glaciers Melting More Quickly"
San Francisco Chronicle (January 26) p. A2, online
External links