The Great London:
Antarctic

The world's largest canyon may lie under the Antarctic ice sheet, according to analysis of satellite data by a team of scientists, led by Durham University.

Although the discovery needs to be confirmed by direct measurements, the previously unknown canyon system is thought to be over 1,000km long and in places as much as 1km deep, comparable in depth to the Grand Canyon in USA, but many times longer.

The canyon system is made up of a chain of winding and linear features buried under several kilometres of ice in one of the last unexplored regions of the Earth's land surface: Princess Elizabeth Land (PEL) in East Antarctica. Very few measurements of the ice thickness have been carried out in this particular area of the Antarctic, which has led to scientists dubbing it one of Antarctica's two 'Poles of Ignorance'.

The researchers believe that the landscape beneath the ice sheet has probably been carved out by water and is either so ancient that it was there before the ice sheet grew or it was created by water flowing and eroding beneath the ice.

Although not visible to the naked eye, the subglacial landscape can be identified in the surface of the ice sheet.

Faint traces of the canyons were observed using satellite imagery and small sections of the canyons were then found using radio-echo sounding data, whereby radio waves are sent through the ice to map the shape of the rock beneath it. These are very large features which appear to reach from the interior of Princess Elizabeth Land to the coast around the Vestfold Hills and the West Ice Shelf.

The canyons may be connected to a previously undiscovered subglacial lake as the ice surface above the lake shares characteristics with those of large subglacial lakes previously identified. The data suggests the area of the lake could cover up to 1250km², more than 80 times as big as Lake Windermere in the English Lake District.

An airborne survey taking targeted radio-echo sounding measurements over the whole buried landscape is now underway with the aim of unambiguously confirming the existence and size of the canyon and lake system, with results due later in 2016.

Lead researcher, Dr Stewart Jamieson, from the Department of Geography at Durham University in the UK, said: "Our analysis provides the first evidence that a huge canyon and a possible lake are present beneath the ice in Princess Elizabeth Land. It's astonishing to think that such large features could have avoided detection for so long.

"This is a region of the Earth that is bigger than the UK and yet we still know little about what lies beneath the ice. In fact, the bed of Antarctica is less well known than the surface of Mars. If we can gain better knowledge of the buried landscape we will be better equipped to understand how the ice sheet responds to changes in climate."

Co-Author Dr Neil Ross from Newcastle University in the UK, said: "Antarctic scientists have long recognised that because the way ice flows, the landscape beneath the ice sheet was subtly reflected in the topography of the ice sheet surface. Despite this, these vast deep canyons and potential large lake had been overlooked entirely.

"Our identification of this landscape has only been possible through the recent acquisition, compilation and open availability of satellite data by many different organisations (e.g. NASA, ESA and the US National Snow and Ice Data Center), to whom we are very grateful, and because of some serendipitous reconnaissance radio-echo sounding data acquired over the canyons by the ICECAP project during past Antarctic field seasons."

Co-Author Professor Martin Siegert, from the Grantham Institute at Imperial College London, UK, said: "Discovering a gigantic new chasm that dwarfs the Grand Canyon is a tantalising prospect. Geoscientists on Antarctica are carrying out experiments to confirm what we think we are seeing from the initial data, and we hope to announce our findings at a meeting of the ICECAP2 collaboration, at Imperial, later in 2016.

"Our international collaboration of US, UK, Indian, Australian and Chinese scientists are pushing back the frontiers of discovery on Antarctica like nowhere else on earth. But the stability of this understudied continent is threatened by global warming, so all the countries of the world now must rapidly reduce their greenhouse gas emissions and limit the damaging effects of climate change."

>The research is >published in >Geology>.

Source: Durham University [January 13, 2016]

Current rates of climate change could trigger instability in a major Antarctic glacier, ultimately leading to more than 2m of sea-level rise.

This is the conclusion of a new study looking at the future of Totten Glacier, a significant glacier in Antarctica. Totten Glacier drains one of the world's largest areas of ice, on the East Antarctic Ice Sheet (EAIS).

By studying the history of Totten's advances and retreats, researchers have discovered that if climate change continues unabated, the glacier could cross a critical threshold within the next century, entering an irreversible period of very rapid retreat.

This would cause it to withdraw up to 300 kilometres inland in the following centuries and release vast quantities of water, contributing up to 2.9 metres to global sea-level rise.

The EAIS is currently thought to be relatively stable in the face of global warming compared with the much smaller ice sheet in West Antarctica, but Totten Glacier is bucking the trend by losing substantial amounts of ice. The new research reveals that Totten Glacier may be even more vulnerable than previously thought.

The study, by scientists from Imperial College London and institutions in Australia, the US, and New Zealand is >published in Nature. Last year, the team discovered that there is currently warm water circulating underneath a floating portion of the glacier that is causing more melting than might have been expected.

Their new research looks at the underlying geology of the glacier and reveals that if it retreats another 100-150 km, its front will be sitting on an unstable bed and this could trigger a period of rapid retreat for the glacier. This would cause it to withdraw nearly 300 km inland from its current front at the coast.

Retreating the full 300 km inland may take several hundred years, according to co-author Professor Martin Siegert, Co-Director of the Grantham Institute at Imperial College London. However, once the glacier crosses the threshold into the unstable region, the melting will be unstoppable -- at least until it has retreated to the point where the geology becomes more stable again.

"The evidence coming together is painting a picture of East Antarctica being much more vulnerable to a warming environment than we thought," he said. "This is something we should worry about. Totten Glacier is losing ice now, and the warm ocean water that is causing this loss has the potential to also push the glacier back to an unstable place."

"Totten Glacier is only one outlet for the ice of the East Antarctic Ice Sheet, but it could have a huge impact. The East Antarctic Ice Sheet is by far the largest mass of ice on Earth, so any small changes have a big influence globally."

To uncover the history of Totten Glacier's movements, the team looked at the sedimentary rocks below the glacier using airborne geophysical surveys. From the geological record, influenced by the erosion by ice above, they were able to understand the history of the glacier stretching back millions of years.

They found that the glacier has retreated more quickly over certain 'unstable' regions in the past. Based on this evidence, the scientists believe that when the glacier hits these regions again we will see the same pattern of rapid retreat.

Author: Hayley Dunning. | Source: Imperial College London [May 18, 2016]

Planetary scientists have discovered pieces of opal in a meteorite found in Antarctica, a result that demonstrates that meteorites delivered water ice to asteroids early in the history of the solar system. Led by Professor Hilary Downes of Birkbeck College London, the team announce their results at the National Astronomy Meeting in Nottingham on Monday 27 June.

Opal, familiar on Earth as a precious stone used in jewellery, is made up of silica (the major component of sand) with up to 30% water in its structure, and has not yet been identified on the surface of any asteroid. Before the new work, opal had only once been found in a meteorite, as a handful of tiny crystals in a meteorite from Mars.

Downes and her team studied the meteorite, named EET 83309, an object made up of thousands and broken pieces of rock and minerals, meaning that it originally came from the broken up surface, or regolith, of an asteroid. Results from other teams show that while the meteorite was still part of the asteroid, it was exposed to radiation from the Sun, the so-called solar wind, and from other cosmic sources. Asteroids lack the protection of an atmosphere, so radiation hits their surfaces all the time.

EET 83309 has fragments of many other kinds of meteorite embedded in it, showing that there were many impacts on the surface of the parent asteroid, bringing pieces of rock from elsewhere in the solar system. Downes believes one of these impacts brought water ice to the surface of the asteroid, allowing the opal to form.

She comments: "The pieces of opal we have found are either broken fragments or they are replacing other minerals. Our evidence shows that the opal formed before the meteorite was blasted off from the surface of the parent asteroid and sent into space, eventually to land on Earth in Antarctica."

"This is more evidence that meteorites and asteroids can carry large amounts of water ice. Although we rightly worry about the consequences of the impact of large asteroid, billions of years ago they may have brought the water to the Earth and helped it become the world teeming with life that we live in today."

The team used different techniques to analyse the opal and check its composition. They see convincing evidence that it is extra-terrestrial in origin, and did not form while the meteorite was sitting in the Antarctic ice. For example, using the NanoSims instrument at the Open University, they can see that although the opal has interacted to some extent with water in the Antarctic, the isotopes (different forms of the same element) match the other minerals in the original meteorite.

Source: Royal Astronomical Society [June 28, 2016]