NGNEWS.com
Scientists spotted the Ninnis Glacier Tongue in the act of
calving January 22, 2000. The resultant iceberg (sections A and
B) has an area of approximately 560 square miles (900 square kilometers).
The Ninnis
Ice Tongue, 350 square miles (900 square kilometers) of floating
ice extending into the Indian Ocean, has broken off the edge of
the continent and is slowly disintegrating.
NASA scientists first spotted the break off in January. The tongue
has been losing mass for some time as part of the normal advance
and retreat of glacier cycles. What is unusual, the scientists
say, is that typically small icebergs calve off the outer edges
of an ice shelf or glacial tongue. In this case the entire tongue
has broken off, changing the face of the coastline of East Antarctica.
Within a week
of breaking off, the berg split in two. Scientists are watching
closely to determine the impact the two bergs will have on the
sea ice and wildlife of the area.
 By
February 20, 2000, Bergs A and B had almost totally separated,
rotated counterclockwise, and drifted to the north. Both sections
are now well away from the Ninnis Glacier.
FLOATING
GLACIERS
An ice tongue
occurs when a glacier flows out into the sea, forming a mass of
permanent ice that is essentially floating while at the same time
attached to the land.
There is no
evidence linking the demise of the Ninnis Glacier Tongue to warming
in the region.
"The
disintegration is likely to be the consequence of a natural progression
of events that periodically occur in floating glacier tongues
around the margin of the Antarctic Ice Sheet," says Rob Massom,
in a NASA report. "What remains a mystery is why these breakouts
occur."
Massom, a
polar research scientist with the Antarctic Cooperative Research
Centre at the University of Tasmania, Australia, was the first
to spot the breakout while studying satellite images.
KEEPING
A CLOSE EYE
In spite of
their importance in assessing global warming and climate change,
the current mass balances (the net gains or losses) of the Antarctic
ice sheets are not known. And the advance and retreat of ice is
extremely dynamic.
Before breaking
off, the tongue of the Ninnis Glacier had lost about two-thirds
of its area since 1913. However, scientists at the Alaska Climate
Research Center report that the nearby Mertz Glacier tongue has
advanced substantially over the same time period.
In March nearly
two thirds of the Ross Ice Shelf broke away in several pieces,
one of them covering an area of 3,900 square miles (10,000 square
kilometers), according to the U.S. National Ice Center. In early
May, three massive bergs with a combined length of around 194
miles (312 kilometers) broke off the Ronne Ice Shelf in the Weddell
Sea.
Scientists
are using historical data and satellite images that have been
collected since the early 1970s to determine annual and decadal
changes in the Antarctic coastline. Without these studies, the
impact of global warming — or whether it's even happening
— cannot be determined.
Massom's study
is one of the first to observe the disintegration of a glacier
tongue virtually as it was happening. He plans to travel to area
in 2002. In the meantime, he is monitoring the movements of the
two large icebergs, which have taken off in different directions.
"The
twin icebergs have behaved quite differently in terms of their
drift patterns since they split apart," said Massom. "This
highlights the complexity of ocean currents in the region, which
are poorly understood."
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