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Phantom Mountains under the Antarctic Ice

The surface of the Greenland ice sheet.
Photo courtesy of Michael Studinger,
Lamont-Doherty Earth Observatory of Columbia University.

An international project probes the world's last great unexplored mountain range. Catch is, it lies under three kilometres of ice.

By Graham Chandler

Fifty years ago, a team of Soviet scientists was conducting a seismic survey as they headed for what is known as the Pole of Inaccessibility, the point in the Antarctic furthest from any coast, when they made a remarkable discovery
- a massive subglacial mountain range that has left earth scientists scratching their heads. According to received theory, it shouldn't be there. Hypotheses had predicted there would be nothing but a vast and somewhat featureless plain much like Canada's interior. 

Land gravity measurement with differential GPS positioning.
Fausto Ferraccioli, Airborne Geophysics Group
Leader of the British Antarctic Survey

"We don't have a clue as to why these mountains should be there at all in the middle of a continent," says Fausto Ferraccioli, Airborne Geophysics Group Leader of the British Antarctic Survey. "It's really a mystery to have a very high mountain range in an old Precambrian region. Typically mountain ranges are created by collisional processes or by extensional processes. But these mountains are really very, very high, and the last collision that happened in East Antarctica was about 500 million years ago, so these mountains should have been basically eroded."

Left largely unexplored for the past five decades except for confirmation by US aerial radar survey in the 1970s, the Gamburtsev Mountains are now front and centre of the international AGAP (Antarctica's Gamburtsev Province) Project, and the British Antarctic Survey is one of the participants. "This is a major flagship project of the International Polar Year," says Ferraccioli, "and it will involve six different countries – the US, Germany, China, the UK, Australia and Japan."

The initiative is led by the Lamont-Doherty Earth Observatory of Columbia University and is not only multinational but also multidisciplinary, "including aerogeophysics, traverse programs, and passive seismic instrumentation complimented by future ice core and bedrock drilling," says Michael Studinger, Doherty Research Scientist at the Observatory and co-chief scientist. The crews expect to be in the field early November 2008 to mid-January 2009.

Land gravity measurement with differential GPS positioning. Project overview for the exploration of the Subglacial Gamburstev Mountains. Courtesy of British Antarctic Survey.
(Click to enlarge

Spurred by the mysterious mountains, four basic questions have arisen that underpin this international team's work. How does topography influence initiation and development of continental ice sheets? How do major mountain massifs form within intraplate settings with no straightforward plate tectonic mechanism? How do tectonic processes control the formation, distribution, and stability of subglacial lakes? (There are lakes under this ice too) Where is the oldest climate record in the Antarctic ice sheet?

To acquire data for some answers, over the past two years the team has been preparing the complex logistics and developing an airborne geophysical system for the project: ice-penetrating radar, LiDAR (Light Detection and Ranging), gravity and magnetics.

It's more than scientific curiosity about the earth's formation processes. Answering these questions will help our understanding of climate change. "One of the fundamental questions in Antarctic science is when, where and how the Antarctic ice sheet formed," says Studinger. "Preliminary ice-sheet modeling suggests the Gamburtsev Subglacial Mountains are the likely location for initiation of the East Antarctic ice sheet, and therefore could be a key factor in understanding the onset of glaciation in the Paleogene 35 million years ago."

He explains that in order to understand the evolution of the Antarctic ice sheet over such long time scales we need to understand the relationship among Antarctic geodynamic processes, ice-sheet dynamics, and global environmental change. "For example mountain uplift can influence climate and thus ice-sheet dynamics," he explains. "In turn, climate change can lead to increased erosion rates and accelerated mountain uplift." It has been suggested that during warmer periods, this terrain was drained first by ice streams and then, nearer the coast, by rivers from which thick sediments accumulated. "We have a conceptual understanding of these processes but it is essential to move towards quantitative models." He adds that a lack of first-order data sets for most of the continent has so far precluded formation of such a model.

Land gravity measurement with differential GPS positioning. Remote field camp and Twin Otter aircraft,
similar to what will be set up at the AGAP north site.
Copyright British Antarctic Survey

It's expected that data gathered during the AGAP project will go a long way towards this end. "We want to find out what these gigantic mountains are and where they come from; because no-one really knows how they formed," says Studinger. "There is really no straightforward explanation as to how you get such high mountains in the interior of a continent." He says the new data will enable us to "uncover" this phantom mountain range, which is larger than the Alps.

Ferraccioli says there are several scenarios, e.g. "that these mountains are actually quite recent, for example they could be related to a hot spot, which is in essence a hot mantle similar to what we've seen in Iceland. This would basically radically change our view of East Antarctica as a sort of stable, Precambrian continent."

Searching for the oldest ice on the planet also provides critical input to knowledge of past climate change, helping our understanding of today's global warming. Ice cores contain valuable preserved records of past atmospheric composition, volcanic eruptions and other environmental information. "In Antarctica, we have drilled at a series of locations and retrieved ice as old as about 900,000 years," says Ferraccioli, which provides a record that far back. "In this particular region, we believe that there may be ice that is over 1.2 million years old and so this would provide us with an unprecedented record of climate change in the past."

Land gravity measurement with differential GPS positioning. Flight testing in Kangerlussuag, Greenland.
From left to right: Jason Preston (Kenn Borek Air Ltd.), Michael Studinger (Lamont-Doherty Earth Observatory of Columbia University), Nick Frearson (Lamont-Doherty Earth Observatory of Columbia University), Adrienne Block (Lamont-Doherty Earth Observatory of Columbia University), Travis Goetzinger (Kenn Borek Air Ltd.), Colin Anderson (Kenn Borek Air Ltd.). Photo courtesy of Michael Studinger, Lamont-Doherty Earth Observatory of Columbia University.

Although the airborne magnetic and gravimetric survey will be able to hint at mineral composition, none of the AGAP research is aimed at mineral exploitation. Copper, lead, zinc, gold and silver have been found on the Antarctic peninsula and oil and gas is most likely present in its sedimentary basins, but by international agreement exploitation has been banned. The 1959 Antarctic Treaty dedicated the continent to peaceful use, established international exchange of scientific data and outlawed new territorial claims; and in 1991 the signatories agreed that "any activity relating to mineral resources other than scientific research" is prohibited. The AGAP project fits: a 1998 follow-on preserved the continent as an archive of the world's climatic past and a barometer of the planet's future.

Part of the reason exploration of this mysterious subglacial topography has been limited is simply logistics. The Antarctic is a forbidding place. Ice covers 98 percent of its land and in winter extends to an area larger than the continent itself. Thirty million cubic kilometres of ice depresses its bedrock by 600 metres and tilts the icesheets towards the centre. It constitutes 72 percent of the world's fresh water yet precipitation is about the same as the driest parts of the Sahara. The record low is –89.2 degrees C. And distances are daunting. "The survey region is about 1000 kilometers away from the South Pole and equally about 1000 kilometers away from Davis and Zhong Shan, which are respectively the Australian and Chinese bases on the other side of Antarctica," says Ferraccioli. "So it's really in the middle of nowhere. It's the highest spot on the East Antarctic Ice Sheet. It's over 4,000 meters high." He compares the challenge with going to Mars. "On the surface, all you would see is a white ice sheet," he says.

The thickness of that ice will be probed by the airborne radar, which can image ice over four kilometres thick. "We can understand the layers of  ice," says Ferraccioli, "which gives you an idea of basically [how] ice ages. The layers can be correlated with future drill sites, which the Chinese are interested in." Eventually a more permanent base for drilling will permit an expensive but revealing entry into the oldest levels of ice and the rock below the ice. "If in five to ten years' time, the Chinese do attempt to drill there, it will only be to sample the rock of this mountain range," says Ferraccioli. "Not for mineral exploitation but really just to try and verify the geophysical interpretations." Even just one drilling effort would help ground-truthing in a large way but still be far from providing the entire picture of the mountain range, he adds.

Land gravity measurement with differential GPS positioning.
US seismic team.
Copyright Douglas A Wiens, Washington University.

The radar will reveal some details on subglacial lakes too, which may be affecting the dynamics of the ice sheet. The glacial lakes are a major objective of the project. "We will be surveying some large subglacial lakes with the aerogeophysical survey," says Robin Bell, Director, ADVANCE Program at Columbia's Earth Observatory. Exploration by remote submersible is on the horizon too. "There are plans to enter both subglacial Lake Vostok and Lake Ellesmere in the next few years but no submersible this season."

The aeromagnetics will provide indications of subglacial geology, by assisting with mapping of possible volcanic regions, major tectonic boundaries and potentially thermal anomalies. "Then we use gravity," says Ferraccioli, "which will give us indications of possible sedimentary basins, the thickness of the crust and will also give us indication of possible anomalies such as density in the upper mantle." A hot spot he says would indicate a low density mantle.

Data gathered will be varied and of a large volume so both standard and specialized software is needed to process them. For example, each four-hour flight will generate 500 gigabytes of data. "It's a large data set with a variety of data streams that differ substantially in size and structure," says Studinger. "This makes the use of multiple software packages necessary." Some of these he says are developed in house using Matlab, for organizing and structuring the data sets and for initial quality control and archiving. 

The gravimeter for the survey will be provided and operated by Sander Geophysics Ltd. who designs and uses its own company software for quality control, data reduction, viewing, and map production. "After initial quality control and archiving of the airborne and ground magnetic data with our Matlab tools we use Geosoft's Oasis montaj for further processing, data analysis and map production," says Studinger. Oasis montaj allows efficient importing, viewing, processing and sharing of diverse earth science datasets and images. "We use the basic airborne geophysics package and several extensions for modeling, filtering, and source depth estimates that enable us to perform state of the art analysis of our airborne magnetic data," he says.

Land gravity measurement with differential GPS positioning.
British Antarctic Survey Twin Otter aircraft
equipped with ice penetrating radar survey gear.
Copyright British Antarctic Survey.

Ferraccioli says potential field data, such as magnetic and gravity, is obviously non-unique, "so we're also going to fit our interpretations with seismology – which in particular will give us indications of the crustal thickness and again possible anomalies in the upper mantle." The potential field data will be processed using Geosoft. "We will be doing gravity and magnetic modeling using GM-SYS." This tool enables design of 3-D models depicting subsurface structures by for example stacking montaj topography grids. 

What will be the prize at the end of the process? "The product will be a new map of the sub-glacial topography of the Gamburtsev sub-glacial mountains province," says Ferraccioli. "We will have new maps of aeromagnetic anomalies over this area. New maps of Free-Air gravity, Bouguer gravity and isostatic gravity maps for the region. Then we will also be producing new crustal models to try and define the uplift of the Gamburstev sub-glacial mountains."
But these two organizations won't be taking all the credit. "Projects of this size are only possible through collaboration between many scientists and organizations from countries around the world," says Studinger. "We see the AGAP project as a model for future science projects in Antarctica."