Cold case

There are lakes in Antarctica. It might seem strange but it's true — bodies of liquid water, some of them hundreds of kilometres long — are locked away under kilometres-thick ice sheets. These lakes, formed from ice melted by the heat radiated from the bedrock, are the most isolated bodies of water on the planet: locked away for hundreds of millennia, with no light, frigid temperatures, and no linkages to any other environments.

But one Antarctic lake is about to see the light for the first time in its existence. In the Southern Hemisphere summer of 2012-2013, a British Antarctic Survey expedition will attempt to drill down through 3.2km of ice to the surface of Lake Ellsworth, a lake about the size of Windermere in the middle of the West Atlantic Ice Shelf — an unprecedented depth of ice drilling. Once the borehole is complete, they will drop a probe into the cold depths to sample the water, dropping it right to the floor of the lake to take a sample of the sediments. They will then take a core sample of the lake bed, returning it to the surface for study. And they will do all of this without contaminating the lake in any way.

A purely quixotic task? Hardly. According to Martin Siegert of the University of Edinburgh, leader of the Ellsworth project consortium, the lake could contain clues to the origin and development of life of Earth; insights into how to search for life elsewhere in the Solar System; and could help us understand how the ice-caps have changed over their history.

'There are three main reasons subglacial lakes are interesting,' he explained. 'They are liquid water in an unusually extreme location, under an ice-sheet on Earth, wherever there is water, there is life, without exception, and understanding how life develops under extreme conditions is fundamental to us. Lake Ellsworth has been untouched and isolated for many thousands of years, without sunlight and under extreme pressure, and we want to find out if there is life in it, and if so, how is it living, surviving, adapting and evolving in whatever ecosystem exists down there.'

The second reason is related to the first, he added. 'Looking for life in a subglacial lake is very similar to the experiments you'd need to do to look for life on Europa, the moon of Jupiter, where there are oceans of liquid water under a thick layer of ice. We have to miniaturise equipment, we have to drill through a significant depth of ice, and we have to measure, sample and return a probe to fully comprehend the chemistry, biology and physiography of it all, and we have to do all of that in a very clean way.' The lessons learned from the Ellsworth expedition will be crucial to the planning of a Europa mission, said Siegert.

Finally, the location of Ellsworth is an interesting one for climate change research. The West Antarctic Ice Shelf is thought to be unstable, Siegert adds, and glaciologists believe it collapsed at some point in the past. Were rising global temperatures to cause a similar collapse today, the water locked in this ice shelf alone would raise sea levels by 6m. 'We know from seismic studies that there are sediments at the bed of the lake, and sedimentology tells us that these sediments will have a record of climate change. If the ice shelf collapsed in the past, they would contain evidence of it and would be able to tell us when it happened.'

The location is also convenient — about 200 miles from a major logistics centre for Antarctica, the Patriot Hills base. Situated at the foot of the hills, the area is scored clean of snow and loose ice by the winds whipping off the high plateau of the ice shelf at the centre of the continent, leaving a surface of clean, hard glacial ice that can be smoothed down and used as a runway. 'We can land big aircraft on it, so we can get equipment near to the centre of the West Antarctic sheet and use a tractor train to get it through to the lake.'

But drilling through 3.2km of rock-hard glacial ice is no mean task, and the need to leave the site pristine makes it even harder. Three and a half years before the expedition is to set off, the Ellsworth project consortium — which includes the British Antarctic Survey, the National Oceanography Centre, Southampton, the Open University, and the universities of Edinburgh, Aberdeen, Durham, Bristol, Northumbria and Belfast — is already well advanced in planning the technology that will help them do it.

The team will use a hot-water drill to bore through the ice — basically a device resembling a showerhead that will spray pressurised water at 70°C ahead of it, melting its way into the ice shelf. This is the only appropriate method, Siegert said. 'You could use a mechanical corer to drill into the ice, but that needs an antifreeze, which raises the possibility of contamination. Or you could use a thermal probe, which has a heated element to melt its way down. But that has a few problems. It freezes itself in as it goes, which makes supplying power and communications very difficult; it also means that you can't get it back, so you can't return samples. Moreover, all the dust and sediment contained in a 3km column of glacial ice distil out ahead of the probe, and they form a barrier it can't melt past, so it'll go sideways. Its path is completely unpredictable.'

The hot-water drill isn't a new technology, but it has never been used to drill to this depth; mostly, it's used for boreholes 1.5-2km deep. The drill head will be produced by the British Antarctic Survey, whose head of engineering, David Blake, explained that the problem wasn't the technique itself, but the ancillary equipment. 'You need to get energy down there; you need to heat the water at the surface and pump it down. So you need a hose, and you couldn't get pressure hose that long until recently. You had to have shorter lengths with couplings, and for these depths, that wasn't practical.' The new hose, over 3km long and weighing some 17 tonnes, will be custom-made by a company that usually supplies the offshore oil industry, Blake said.

The drilling will take place in two stages. First, the team will melt surface snow, sending it through jet-fuel-burning boilers to heat it to 70°C, and make a borehole some 400m deep. At this level, the ice was deposited before the Industrial Revolution, and contains none of the atmospheric pollutants associated with heavy industry. 'We melt out a cavern at that level, which gives us a reservoir of clean water,' Siegert said. 'Then we bring that to the surface, irradiate it with UV light and biofilter it, to make sure it's completely clean, heat it, and pump that into the drill head to make our main borehole. We recirculate the water that we melt, so by the time we get to the surface of the lake itself we will be putting some water into the lake, but only from the ice immediately above it — which is what the lake is made of anyway.'

The probe to carry out the studies of the lake is another bespoke device, to be built at the National Oceanographic Centre under the direction of Matt Mowlem, a veteran in designing deep-sea probes. Built under strict clean-room conditions, the probe's pressure hull will contain sample chambers for water and sediment, and an array of current meters to detect and measure the flow of water in the lake, as well as chemical sensors to determine what's in it. 'We want to have as much on board as we can, because we can't be 100 per cent certain we'll get it back,' Blake said. 'But the plan is to send the samples of water and sediment back to the BAS labs in Antarctica for thorough analysis.'

Once the probe has been recovered, the team will send down a mechanical coring device to remove a 3m column of sediment, whose layers will hold the history of the lake bed. 'We may not have time to do that,' Siegert said. 'There will be about a dozen people there actually doing the drilling, but we'll have scientists on site —including me — who will take those decisions.'

The main tasks now, apart from the technology, are logistical. Some 300 drums of fuel need to be stockpiled at the site, and Siegert hopes to send the first of these to Patriot Hills in the upcoming Antarctic summer. He will soon start negotiations with the other signatory nations of the Antarctic Treaty, to inform them of the consortium's plans. After that, a round of tests will begin to confirm that both drill and probe will perform as they are supposed to, and to train the crew. 'We can't have it break on us,' he said. 'And everyone has to know exactly what they're doing. This is a major expedition, and we're hoping for some breakthroughs.'