Pinhole technology to search for the oldest ice

Few people in the world have had as much experience with drilling ice cores as Bernese physicist Jakob Schwander. He is now working at the Oeschger Centre on the development of ultra-light drilling equipment to be used to search for 1.5 million-year-old ice in Antarctica. Last summer, the new technology proved itself in Greenland.

Today, 30 years later, Schwander's vision is finally being realised. His idea about pinhole technology has turned out to be feasible, and is due to play an important part in an ambitious research project: the search for the oldest ice core. Researchers from the Oeschger Centre are at the forefront of this international initiative, whose purpose is to drill ice in the Antarctic containing information about the climate of the last 1.5 million years - it is hoped the core will go back almost twice as far as the oldest ice so far analysed.

Change of rhythm between warm and cold

One major purpose of looking back into the climate of the past is to try to gain a better understanding of the interplay between warm and cold periods. Investigation of marine sediments has shown that about a million years ago there was a dramatic change in the regular alternation of these periods. In the period before what is known as the Mid Pleistocene Transition, ice ages and warm periods alternated every 41,000 years or so, but afterwards every 100,000. Why this change occurred is a puzzle, but climate scientists suspect that greenhouse gases played a decisive role. It is hoped to confirm this conjecture by drilling into the oldest ice on Earth.

The fact that ice 1.5 million years old exists, and the areas of the Antarctic where it is to be found has been shown in a recent study by Hubertus Fischer of the Oeschger Centre. Now an exploratory borehole using the pinhole technology is to show exactly where it would be worthwhile to drill. The apparatus to be used for this is no bigger than an electric toothbrush, and the prototype drill produced with a 3D printer looks quite nondescript lying on Jakob Schwander's desk. It works on what is known as the Moineau principle, where the motor is driven by the fluid that circulates between the ice surface and the drill. Jakob Schwander has already tested the prototype. "We could show that the technology works, in principle." But more on that later...

No more than two planeloads of material

The procedure that Schwander is contemplating apparently so nonchalantly, sounds completely incredible. The two centimetre narrow hole that he wants to drill is supposed to go down at least 2.5 kilometres to the bedrock under the Antarctic ice sheet. And drilling is to take less than two weeks. "Rapid access drilling" is the name of the technique. Its big advantage is its minimal logistical requirements. Conventional ice drilling at this depth calls for more than 40 tonnes of drilling fluid. But the Bernese drillers want to manage with one tonne. "In all we want to restrict ourselves to two tonnes of material," says Jakob Schwander. "That's the idea underlying this project." The goal is to be able to transport all the equipment to the drill site in the middle of the Antarctic using no more than two Twin Otter aircraft.

It is not only non-specialists who are astonished at this plan, but also other research groups who are also trying to develop a "rapid access" method, chiefly in France and the US. The ice drilling specialists recently held a workshop where they presented their plans to each other. This also included the filter system used to separate the drill cuttings, which are used to determine the age of the ice, from the drilling fluid. The Americans are planning a piece of apparatus the size of a shipping container, while Jakob Schwander's is to be no bigger than a beer crate.

The Bern University physicist is relying not only on decades of experience with his project, which bears the name RADIX (minimal resources rapid access drilling system) and is supported by the Air Liquide Foundation. He has demonstrated mathematically the feasibility of the pinhole technology. He worked out a formula that takes a dozen parameters into account - from the speed of drilling to the pressure that the borehole has to withstand - and then calculates the smallest possible diameter. "I'm glad that my intuition didn't let me down; a borehole diameter of two centimetres should be possible," he says of the results of his calculations.

Test drilling in Greenland

The scientist, who has developed into an engineer over the course of 30 years working in ice core research, has thought of everything in connection with his contribution to the search for the oldest ice. Lying on his desk is not only the Moineau drill, but also a modified drill head and a piece of the Kevlar-strengthened hose that is to be used in the polar ice. And in his office in the bowels of the Exact Sciences building at the University of Bern, Jakob Schwander has also thought deeply about how the 2.5 kilometre-long hose is likely to behave in the borehole. For example, which drill fluid can ensure that the ice cuttings actually work their way up in the space between the hose and the wall of the borehole?

Various test drillings delivered the answers to this and numerous other open questions. The testing began on the Pleine Morte glacier in Switzerland, and continued under polar conditions on the Renland peninsula in Greenland, and finally on the Northeast Greenland Ice Stream, where Jakob Schwander and his colleague Barbara Seth participated in the international ice core project EGRIP.

During the test drillings, temperatures of -31°C posed new and unexpected challenges for the researchers from Bern: between the ice and the hose, so-called shrink columns formed. Luckily, they could be sealed off with construction silicone. "It was a coincidence that it worked,” says Jakob Schwander. “In Antarctica we'll have to find another solution."

The physicist is very satisfied with how the drill performed in Greenland's ice. In just 90 minutes, the drill managed a depth of 20 metres - about as fast as he's planning to drill in Antarctica. "Hardly anybody has ever drilled through so much ice in such a short time," grins Schwander, "and that in some of the worst weather I've ever experienced." Now there are various technical and logistical problems to solve to ensure that RADIX is ready for the search for the perfect drilling site for the "Oldest Ice" project. The plan is to start at the end of 2017. Never short of ideas, the developer is optimistic. "We have solutions for every existing problem. Now we’re just running out of time."

Towards the end of the decade, at the cost of between 30 and 50 million euros, the "Oldest Ice" project will hopefully be crowned with success. Pinhole boring will not be sufficient for the drilling of the actual ice core, however: for this, conventional technology will be required. The reason is that so many research groups are interested in the oldest ice that the core must have a diameter of at least ten centimetres in order to provide enough sample material for all the analyses that are planned.

(2016)

Test drilling on Plaine Morte Glacier, Swiss Alps

International ice core project EGRIP on the Northeast Greenland Ice Stream