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Subglacior : A revolutionary probe to explorer ancient climates
If we want to follow the thread of our climate history back over hundreds of millions of years, there is only one way to do so: to dig into the ‘libraries of the past’ in which molecules of water or air from previous millennia have been preserved. In this respect, the Antarctic ice cap is the best library we have, some models suggesting that it contains ice up to 1.5 million years old!
Until now, the climatologists’ approach was to drill, metre by metre, into the thick snow mantle, bring up ice cores and then analyse them back at the laboratory. This is a gradual, painstaking task, with a dozen people working over several years in extreme conditions. “The worst thing of all is, after all these years of toil, when you finally get down to the oldest layers, i.e. the most interesting layers, you sometimes discover that they cannot be used because the layers have become mixed up or because melting has occurred against the rocky base,” reveals Jérôme Chappellaz, a research scientist at the Laboratory for Environmental Glaciology and Geophysics (LGGE) at Grenoble.
To solve this problem, he came up with the idea of inventing a much faster system that would enable the probe to take continuous measurements in real time as it penetrates down into the glacier. This would allow the climatologists not only to ensure the integrity of the deepest layers but also to deliver key information on such items as the age of the different layers, within the space of a few weeks.
“ This new probe will not replace all the data that a real ice core brought up to the surface can give us, but it will enable us to select the best drilling sites and provide us with some valuable information in just a few weeks. ”
Laboratory for Environmental Glaciology and Geophysics (LGGE) at Grenoble
From gnawing doubt sprang a new idea…
Serious doubts can sometimes lead to great discoveries. Jérôme Chappellaz worked out his idea for a new type of probe while he was taking part in a European drilling expedition to the Antarctic in 2007. “We were going down about 20 metres per day and the information that we were looking for was situated right at the bottom, at a depth of over 1,700 metres! So what if those final metres of ice could not then be used? This question going round in my head used to keep me awake. And then, one sleepless night, I suddenly thought that instead of wasting this enormous amount of time bringing the ice cores up to the surface for analysis, we might be able to lower our measuring instruments down directly into the glacier.”
In reality this idea arose from several years of serious thought. The French glaciologist, who loves to tinker with instruments, had actually been working with colleagues at the interdisciplinary physics lab at Grenoble since 2004 on a new laser-based system for analysing ice. "Those colleagues had developed a new technique for measuring molecules in trace amounts and they were looking for a concrete application for it. I suggested testing out their instrument on ice cores, and it worked to perfection!” Jérôme recalls. In fact the new instrument proved to be more sensitive, more convenient and less costly than those which had been in use before.
Betting on the new approach
So wouldn’t it be possible to embed the instrument in the drilling probe and take ‘live’ measurements? They decided to take on the bet. First of all they had to miniaturise the instrument so that it would fit into a tube just 7cm in diameter, find a way to protect it from extreme temperatures as low as -50°C, transfer the data in real time via an electro-carrier cable 3,500 metres in length. It was also necessary to manufacture a drill bit capable of drilling non-stop so as to continuously feed the measuring instrument with snow samples – and all this without too high energy consumption: “Our solution was to incorporate into the drill bit a ceramic element 2cm in diameter, heated by electrical resistance. Around it, the blades cut into the ice, which improves the drilling technique without the need to supply any extra energy.“ Lastly, they had to find a way to evacuate the ice chips that were accumulating inside the hole. “A silicon oil possessing a specific degree of viscosity was specially designed for this purpose. Tests carried out in a cold chamber demonstrated that the chips didn’t become packed together,” explains Jérôme. The oil was pumped down and around from the surface, circulated back and was then filtered so that it could be re-used continuously.
Antarctic here we come…
This was how Subglacior – whose name is taken from the fantasy submarine in which cartoon characters Blake and Mortimer enjoyed a ride through the Antarctic subglacial Lake Vostok – came into being. “We tested a first prototype in summer 2014 in the waters of the Mediterranean Sea and we were very satisfied with it. And by the way, the oceanographers are now interested in this instrument as well,” claims Jérôme Chappellaz. The next step will be to ship all the equipment out to the scientific base at Dumont d’Urville in Antarctica in late 2015, and then use the tractors belonging to the French Polar Institute to transport it to the Concordia Base in the middle of the continent. The first test is scheduled for 2017.
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