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Mardi, 11 Octobre 2011 16:00

Geologists Prepare to Drill Into Ancient Antarctic Lake

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Geologists Prepare to Drill Into Ancient Antarctic Lake

By Olivia Solon, Wired UK

A team of British researchers are preparing to dig down through three-kilometer-thick ice to sample a lake under the Antarctic in the hope of finding new species and clues about the future impact of climate change.

A team of engineers with 70 tonnes of gear are to head for Lake Ellsworth in West Antarctica. The lake has been isolated from the outside world for at least 125,000 years — but it could be as many as a million. It’s about 10km long and two to three kilometers wide.

The team’s mission is to prepare the way for the “deep-field” research mission that will take place in October 2012. They will then use hot water to melt through 3,000 meters of ice in order to reach the lake, which remains liquid due to geothermal heat coming from inside the Earth. This technique has been used before in Antarctic experiments, but never this deep. The hot water drill will need to operate continuously for three days to create a 36cm wide borehole through the ice.

Engineer Andy Tait, from British Antarctic Survey, explains: “The design of the hot water drill is very straight-forward – very similar to the hot water you might use on a jet spray to clean a car. The nozzle delivers water at 2,000 psi and 90C which is needed to melt the ice to create the hole.”

Finding a hose long enough for the job was a big challenge. Tait explains: “Drilling such a long hole requires a long hose – this is particularly difficult to find companies capable of producing a continuous hose of 3.4 kilometers. The hose needs to be strong enough to support not only its weight, but the weight of the drill nozzle on the end of it.”

The -20C temperatures inside the borehole means that its diameter reduces by 0.6 cm per hour, as the water refreezes. This leaves a window of around 24 hours in which to conduct all of the experiments before the hole becomes too narrow.

Once it has penetrated the lake they hope to gather samples of lake water and sediment.

A probe — comprising of two pressure cases containing instrumentation and power and communications — will be sent down the borehole. Water will be sampled and archived at predetermined intervals, with an on-board microprocessor and data logger running continuously. A separate instrument will be sent to the bottom of the lake to hammer into the sediment and collect samples.

The team will be looking for life in the sub-glacial lake. If they find it, it will be a significant discovery, because it will have survived under high pressure, in complete darkness and in isolation for up to a million years.

In addition to looking for life forms in the lake, they will be studying the potential future impact of climate change. If the West Antarctic Ice Sheet completely melts, it thought that it could raise sea levels globally by at least three meters — and perhaps seven meters. However, that’s not expected to occur for several hundreds of years.

One of the main challenges has been building equipment that can withstand the huge pressures and freezing temperatures. Matt Mowlem from the National Oceanography Center in Southampton, which was responsible for building many of the instruments, told the BBC: “This is an unknown environment — we don’t know, for example, whether there will be dissolved gases in the water. So the water at its pressure of 300 atmospheres will be sampled. But when we pull the probe up and the flasks hit the cold air in the borehole, the water will try to freeze; the pressure then increases to around 2,700 atmospheres, and that’s greater than anything experienced in ocean engineering.”

So far, no-one has been able to sample any sub-glacial lake in Antarctica. A Russian team was forced to delay a mission to drill into Lake Vostok earlier this year. Meanwhile an American team is preparing to drill into Lake Whillans.

One of the main challenges has been testing the drilling technology. Tait explains: “Making equipment that is going to be robust enough to work in the environment at -20C is certainly a challenge. Many of the components that you need to create a system aren’t designed for such low temperatures. Many of the companies that provide equipment won’t provide guarantees. Cold testing is of great issue in order that we have the confidence that this equipment, having been transported half way round the world will work the first time that we use it.”

To keep track of the expedition, check out the Ellsworth website.

Image: Illustration of the Antarctic ice drilling process. (University of Edinburgh)


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