Antarctic Ice Tongue Disintegrating

December 13, 2000

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

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.

<tr<td<img src="ninnis.jpg" width=216 height=302 border=0

<FONT SIZE=3 FACE="Times New Roman, Times, Palatino, Serif"

COLOR="#000000"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.</I</FONT</td</tr>

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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."

Comments? Contact <a href="mailto:">Hillary Mayell</a> or nationalgeographic.com news editor <a href="mailto:">David Braun</a>.

<LI> The Ninnis is one of two prominent floating glacier tongues that extend into the Southern Ocean from the coast of King George V Land.

<LI> In January this year the entire Ninnis Ice Tongue broke off.

<LI> Usually smaller icebergs calve off the perimeters of an ice tongue.

<LI> This is the first time scientists have been able to watch, via satellite images, the break up of a huge ice tongue as it happens.

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. 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 usually small ice bergs calve or break off the outer edges of the tongue. In this case the entire tongue has broken off, changing the face of the coastline of East Antarctica.