Antarctic Ice Shelf Thinning from Above... and Below

One of Antarctica's largest ice shelves is thinning from above and below, helping scientists finally understand just what exactly is causing this rapid ice melt, according to new research.

The Larsen C Ice Shelf - whose neighbors Larsen A and B, collapsed in 1995 and 2002 - has long puzzled scientists. They have debated for decades whether warming air temperatures or warmer ocean currents are behind the collapse of the Antarctic Peninsula's floating ice shelves.

But new findings, published in the journal The Cryosphere, is shedding light on this phenomenon, and Antarctica's likely contribution to future sea-level rise.

Using a combination of satellite data and radar surveys, the research team studied the Larsen C Ice Shelf for 15 years, from 1998-2012. Over that time period, they found that this slab of ice lost an average of 4 meters (13 feet) of ice, and had lowered by an average of one meter (~3 feet) at the surface.

"What's exciting about this study is we now know that two different processes are causing Larsen C to thin and become less stable. Air is being lost from the top layer of snow (called the firn), which is becoming more compacted - probably because of increased melting by a warmer atmosphere. We know also that Larsen C is losing ice, probably from warmer ocean currents or changing ice flow," lead author Dr. Paul Holland from British Antarctic Survey (BAS) explained in a press release.

"If this vast ice shelf - which is over two and a half times the size of Wales and 10 times bigger than Larsen B - was to collapse, it would allow the tributary glaciers behind it to flow faster into the sea. This would then contribute to sea-level rise," he added.

It is no secret that much of Antarctica, not just the Larsen C Ice Shelf, is melting faster than ever. The Antarctic Peninsula is one of the fastest warming regions on Earth, with a temperature rise of 2.5 degrees Celsius over the last 50 years.

While the research team continues to closely monitor the ice shelf, they predict that it could completely collapse within the next century, or sooner.

Even more concerning is that a crack is forming in the ice, which could cause it to retreat back further than previously observed. In addition, the ice shelf also appears to be detaching from a small island called Bawden Ice Rise at its northern edge.

"When Larsen A and B were lost, the glaciers behind them accelerated and they are now contributing a significant fraction of the sea-level rise from the whole of Antarctica. Larsen C is bigger and if it were to be lost in the next few decades then it would actually add to the projections of sea-level rise by 2100," said Professor David Vaughan, glaciologist and Director of Science at BAS.

"We expect that sea-level rise around the world will be something in excess of 50 cm higher by 2100 than it is at present and that will cause problems for coastal and low-lying cities," he continued. "Understanding and counting up these small contributions from Larsen C and all the glaciers around the world is very important if we are to project, with confidence, the rate of sea-level rise into the future."

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