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Antarctic

Antarctica's Larsen C ice shelf: new rift detected

Where a trillion-ton iceberg calved last week, researchers have detected a new rift. The concern is that the Larsen C ice shelf will destabilize and collapse, releasing glacial ice into the sea.

A new rift has been detected in the Larsen C ice shelf in Antarctica - just a week after one of the largest icebergs ever recorded broke off from it.

Researchers at Project MIDAS, which has been monitoring the ice shelf and first detected the iceberg's calving, say the new rift appears to be extending northward.

They point out that although this new rift will probably turn toward the shelf edge, creating a small iceberg, there is a risk it will continue toward the Bawden Ice Rise, a point that is crucial to keeping the shelf stable.

"We see a new short feature of around 6 kilometers [3.7 miles] heading north from the complex region of cracks that formed just before the iceberg broke away," said Adrian Luckman, a professor of glaciology at Swansea University, who is leading the research at MIDAS.

Luckman says that researchers will continue to monitor the new rift, and that there is "no cause for concern" just yet.

At present, its tip is "stuck" in a suture zone - that is, a region of softer ice - Luckman said, and is not likely to spread for some time to come.

Colossal iceberg breakaway

The new rift follows news that a colossal iceberg the size of Delaware, since named iceberg A68, broke away from the same Larsen C ice shelf last week.

The 6,000-square-kilometer (2,200-squre-mile) iceberg, now adrift in the Weddell Sea, has already left the ice shelf 12 percent smaller in area.

Breakaways of icebergs are part of a natural cycle and are not in themselves a cause for concern, says Bryn Hubbard, director of the center of glaciology at Aberystwyth University and also a researcher for Midas. "There's nothing unusual about an iceberg being formed by rifting," he says.  

Snow falls on the continent, compacting into ice that constantly flows toward the ocean. As a result, the ice shelf grows by an average of 760 yards (700 meters) each year. At some point, a section breaks away and the ice shelf begins to grow again.

Scientists not unduly worried - yet

Problems would arise if the A68 break - or new rifts - caused the Larsen C ice shelf to become unstable and collapse, as Larsen A did in 1995, followed by Larsen B in 2002. 

Scientists have attributed these collapses and the retreat of several Antarctic ice shelves in recent decades to global warming.

Shelves of sea ice are important because they hold back inland glaciers. The concern is that if Larsen C collapses, ice from glaciers would flow into the sea and melt, raising sea levels.

However, Hubbard says scientists are not unduly worried about the Larsen C ice shelf catastrophically failing at this stage.

"You would expect some short-term instability, given this large chunk has now carved off," he said. There is a risk of it failing, he says, but "modeling indicates that the ice shelf will still be stable following the iceberg carving."

Luckman added that, "instability, if it ever arises, is a long, long way off" and the latest rift is not proof that the ice shelf is already becoming unstable, or that it is likely to.

Climate change culprit

Watch video 01:10

Drifting north: A68 moves away from Antartica

Are the colossal A68 iceberg, and the newly formed rift, signs of human induced climate change? 

Hubbard says it's an impossible question to answer. "Asking if it's linked to global warming is a bit like asking if a given storm surge, or a given warm week, is linked to global warming," he said.

Although climate change research has developed to the point that it is possible to connect specific weather events to a likelihood of having been a result of climate change, in the case of this iceberg, "It's a completely normal process, so you cannot say definitively yes or no."

Take the highest wave in an ocean storm, Hubbard points out; "People ask if the highest wave is caused by climate change. You can't really say that the highest wave is caused by sea level rise. But the sea level is rising, which means in general the highest wave is always going to be a little bit bigger."

Researchers at MIDAS stress that although instability is unlikely, we do not yet know for sure what will happen. "It was always difficult to know when A68 was going to carve off, so we're into the same sort of informed guesswork as with that," said Adam Booth, a lecturer in exploration geophysics at the University of Leeds, and also working for MIDAS.

"What we can do is continue to monitor."

The Antarctic is a highly complicated system, and scientists haven't been monitoring long enough to detect trends and make forecasts yet. "So it's interesting to see how ice shelves do react to carving events like this," Booth concluded.

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