With the
calving, the Larsen C ice shelf lost more than 12 percent of its total surface
area—larger than the US state of Delaware
An iceberg
the size of Delaware, one of the largest on record, was set adrift after
snapping off a West Antarctic ice shelf that is now at increased risk of collapse,
scientists said Wednesday.
A crack in
the Larsen C ice shelf, a drifting extension of the land-based ice sheet,
finally broke through after inching its way across the ice formation for years.
The calving
of ice shelves occurs naturally, though global warming is believed to have
accelerated the process. Warmer ocean water erodes the underbelly of the ice
shelves, while rising air temperatures weaken them from above.
The calving
created an iceberg about 5,800 square kilometres (2,200 square miles) big, with
a volume twice that of Lake Erie, one of the North American Great Lakes. It is
about 350 metres (1,100 feet) thick.
"The
iceberg weighs more than a trillion tonnes, but it was already floating before
it calved away so has no immediate impact on sea level," said a team of
researchers from the MIDAS Antarctic research project.
It will
likely be named A68.
"The
calving of this iceberg leaves the Larsen C Ice Shelf reduced in area by more
than twelve percent, and the landscape of the Antarctic Peninsula changed
forever," the team added.
Separation
occurred somewhere between Monday and Wednesday, and was recorded by a NASA
satellite.
Icebergs
calving from Antarctica are a regular occurrence. But given its size, this
behemoth will be closely watched for any potential risk to shipping traffic.
The fate of
the berg is hard to predict. It may stay in one piece, or break up.
"Some
of the ice may remain in the area for decades, while parts of the iceberg may
drift north into warmer waters," said lead investigator Adrian Luckman.
According
to the European Space Agency, ocean currents could drag the berg, or pieces of
it, as far as the Falkland Islands, posting a threat for ships in the Drake
Passage.
Records
show that large icebergs from the western Weddell Sea, where Larsen C is, tend
to make their way into the Antarctic Circumpolar Current, which flows clockwise
from west to east around the southernmost continent, or into the South
Atlantic.
Will it
collapse?
This may
heighten the risk of the remaining shelf disintegrating.
Floating
ice shelves are fed by slow-flowing glaciers from land. Without them, the
glaciers would flow directly into the ocean.
With its
new shape and size, Larsen C may be less stable than before, the team warned.
"There
is a risk that Larsen C may eventually follow the example of its neighbour,
Larsen B, which disintegrated in 2002 following a similar rift-induced calving
event in 1995," they said. d Larsen A collapsed in 1995.
If the
glaciers held in check by Larsen C were to spill into the Antarctic Ocean, it
would lift the global water mark by about 10 centimetres (four inches), other
researchers have said.
Swansea
University glaciologist Martin O'Leary, another MIDAS project member, said this
is the furthest back Larsen C's ice front has been in recorded history.
"We're
going to be watching very carefully for signs that the rest of the shelf is
becoming unstable," he said in a statement.
"In
the ensuing months and years, the ice shelf could either gradually regrow, or
may suffer further calving events which may eventually lead to
collapse—opinions in the scientific community are divided," added Luckman.
"Our
models say it will be less stable, but any future collapse remains years or
decades away."
Human
actions have lifted average global air temperatures by about one degree Celsius
(1.8 degrees Fahrenheit) since pre-industrial levels, according to scientists.
Antarctica
is one of the world's fastest-warming regions.
O'Leary
said "we're not aware of any link to human-induced climate change"
for the latest calving.
Read more
at:
https://phys.org/news/2017-07-trillion-tonne-iceberg-antarctica-scientists.html#jCp
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