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Climate Hustle

Discovery exposes fragility of Antarctica’s Larsen C ice shelf

Posted on 30 June 2016 by Guest Author

This is a re-post from Carbon Brief by Roz Pidcock

Scientists have unearthed a 100m-thick river of ice beneath Antarctica’s Larsen C ice shelf, which they fear could accelerate its path to eventual collapse.

A team led by Prof Bryn Hubbarddirector of the centre for glaciology at Aberystwyth University in Wales, lived on the ice shelf for several months examining what it looks like from the inside.

Their new paper describes how the layer of solid ice could be speeding up the flow of ice to the ocean, potentially leading Larsen C towards a similar fate to its now-collapsed sister ice shelves, Larsen A and B.

In January, Hubbard was awarded the prestigious Polar Medalin recognition of his services to polar science. He joins an illustrious list of explorers and pioneers, with Captain Robert F Scott, Sir Ernest Shackleton, Sir Edmund Hillary and Sir Ranulph Fiennes among its former recipients.

Carbon Brief has been speaking to Hubbard about his new research, the future of Antarctica and his reflections from a life spent on the ice.

‘Catastrophic breakup’

For more than 25 years, Hubbard has been studying the world’s icy expanses, venturing out each year to live and work on the ice for months at a time. He tells Carbon Brief:

“I am extremely fortunate to be able to recount research field trips to Greenland, Svalbard, Arctic Canada, as well as Antarctica (while most of my early research was actually undertaken in the Swiss and French Alps).”

Hubbard’s latest study has taken him to Larsen C ice shelf in Antarctica, a floating mass of ice protruding from the Antarctica Peninsula in the northern part of the continent.

Several major ice shelves have collapsed almost completely, losing the vast majority of their mass in just a few months. The most widely reported of these “catastrophic breakup events” were the Larsen A and B ice shelves, which collapsed in 1995 and 2002, respectively.

Larsen C is the next ice shelf in line, geographically-speaking. It is also the largest of the three sister shelves, with a surface area two and a half times the size of Wales.

Gif showing the disintegration of Larsen B ice shelf

Credits | Images: NASA Earth Observatory. Gif: Rosamund Pearce for Carbon Brief.

Meltponds

The Antarctic Peninsula is one of the fastest warming places on Earth. Temperatures have risen by 2.5C in the past 50 years. Warmer air is causing the surface of the ice to melt, forming pools of water known as “meltponds”.

Meltponds tend to form in a line “like a string of sausages” and are thought to have contributed to the collapse of ice shelves in the past, including Larsen B. Hubbard tells Carbon Brief:

“We started the work on Larsen C Ice Shelf for the simple reason that satellite images and a small number of aircraft flyovers indicated that melt ponds were forming on their surface regularly.”

Until now, scientists had suspected that meltponds exerted stress through the sheer weight of the water pushing down on the ice below it. But Hubbard and his team wondered if there was a different explanation. He tells Carbon Brief:

“The rationale for our project was to investigate whether the ponds had an influence on the internal structure of the underlying ice shelf.”

Drill deep

With the logistical support of the British Antarctic Survey, Hubbard and his team camped on the ice in traditional ‘Scott’ tents for several months in the summer of 2014/15.

The team drilled a 100m-long borehole in a part of the Larsen-C ice shelf called Cabinet Inlet, where scientists first spotted meltponds 15 years ago.

Just a few metres below the surface, they struck upon a layer of solid ice about 100 metres thick, formed as water from the meltponds percolates through the ice and refreezes.

The discovery was startling, says Hubbard, not only because of the ice layer’s thickness but because of its proximity to the surface. He tells Carbon Brief:

“Upon drilling our borehole in Cabinet Inlet, we were pretty amazed that the drill struck something solid at a depth of only 3m below the surface…To my knowledge, this is the first time that anybody has encountered massive ice of this nature.”

At these shallow depths in other ice sheets, such as Greenland and East Antarctica, scientists have found compacted snow, stacking up in layers as more snow falls on top. Solid ice is usually found much deeper, more like 50-70m below the surface, Hubbard explains.

Schematic showing the discovery of a massive ice layer beneath the surface at Cabinet Inlet on the Larsen-C ice shelf

The discovery of a massive ice layer beneath the surface at Cabinet Inlet on the Larsen-C ice shelf, Antarctic Peninsula. Source: Hubbard et al., (2016).

Cause for concern

The vast icy layer below Larsen C is a concern, says Hubbard. It is warmer than the compacted snow it replaced because of the latent heat that is released as the percolating meltwater refreezes at depth. Thi, in turn affects how the ice moves, Hubbard explains:

“Similar to syrup, warm ice flows more readily than cold ice.”

Hubbard and his team installed a string of instruments to take measurements within the icy layer, returning to collect the data a year later. They found temperatures of between -5C and -10C, a full 10C above what they expected for this depth range. Hubbard says:

“This suggests that not only is the massive ice layer denser than that which would be present in the absence of surface ponds, but that it is also substantially warmer, both having implications for the movement and stability of the ice shelf.”

Using ground-penetrating radar and satellite instruments, the scientists estimated that the icy layer was 16 km wide and several kilometers long. While icy layers have been found elsewhere in Antarctica, the Larsen-C discovery is exceptionally large. Hubbard tells Carbon Brief:

“In east Antarctica, working with the Belgians out of their (carbon neutral) Princess Elisabeth research station, we also found internal ice layers – but at the less extreme end of the scale.”

Nevertheless, it will be sometime before the consequences for Larsen-C are fully understood, Hubbard adds:

“We cannot really determine the implications yet without running all of the information for the entire ice shelf in a computer model, and unfortunately we do not have all of that information yet.”

Other recent research points to a thinning of Larsen C by four metres from 1998-2012, putting it at greater risk of collapse. Ice shelves can also melt from underneath as the ocean warms.

Hubbard suspects vast icy layers could be discovered in many of Antarctica’s other ice shelves in the coming decades. He says:

“[The changes we report] can in all likelihood be anticipated at an increasing number of Antarctica’s fringing ice shelves – and perhaps all of them – over the next century or so as surface warming continues.”

Since ice shelves float on the water, when an ice shelf collapses entirely it doesn’t directly affect sea levels. But once an ice shelf disappears, there’s little to stop the glaciers behind it from flowing into the ocean, causing sea level to rise faster.

A life less ordinary

Hubbard’s research has led him to some of the world’s most inhospitable landscapes. Part of the reason the ice layer below the surface of Larsen C hasn’t been discovered until now, he says, is because of the logistics of carrying out this kind of research in such a challenging place.

But Hubbard looks back fondly his quarter-century of polar expeditions, telling Carbon Brief:

“Each and every one of these trips has been interesting for various reasons; always challenging, always amazing, often fruitful, and occasionally somewhat disastrous.”

Hubbard’s services to science were honoured earlier this year, collecting the distinguished Polar Medal for his outstanding contribution to science under conditions of extreme hardship.

At the time, Prof April McMahon, vice-chancellor of Aberystwyth University called the award “a just recognition of a life dedicated to the discipline.” She added:

“Professor Hubbard and his colleagues at the Centre for Glaciology are at the cutting edge of understanding the effects of climate change on some of the Earth’s most extreme and inhospitable places, and of developing the scientific models that will help us understand better how our planet is likely to respond to an increasingly warm environment”.

Despite the challenges, Hubbard says always seems to go back for more. Though what keeps drawing him back is a mystery, he says:

“To tell the complete truth I don’t even like the cold.”

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Comments

Comments 1 to 1:

  1. To put the Hubbard's numbers into perspective, one must know the thickness of the iceshlf itself. A number which is very obvious to Hubbard himself having lived there for years, but not obvious to outsiders.

    Wikipedia lists iceshlf thickness around the world as varying from 100m to 1000m https://en.wikipedia.org/wiki/Ice_shelf

    Surviving Larsen shelves appear to be around 220m (parhaps 200m to 300m) https://en.wikipedia.org/wiki/Larsen_Ice_Shelf.

    So "a 100m-thick river of ice" appears to be up to scale on the last figure, occupying roughly upper half of Larsen C shelf.

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