by Jean-Louis Tison.
To answer this question, you first need to know the length (and therefore the time span) of the ice core that you wish to extract from the ice sheet.
If you are only interested by a short core a few to 10 meters long, for example to study the properties of the snow and firn (transition from snow to ice) you can use a simple and lightweighted system, entrained manually or with a small motor at the top.
At the other extreme, if you want to recover 3000 meters of ice, all the way to the bottom of the ice sheet, covering up to 800.000 years, you need to gather all your friends internationally (and a lot of money!) for an international drilling program that might last more than 5 years (summers in the field).
In that case, the drill is much more complex and send down the hole with the motor on top of the drill barrel, which is made of an upper container (tube) to collect the chips from the cutting of the ice, and a lower one to collect the core. At the bottom of the latter is the drilling head, equipped with 2-3 knives, that digs an annular hole, isolating the core from the ice sheet.
The cutting chips are pushed up an “archimede’s screw” on the outside of the inner tube, where the core is collected. The chips are contained by an outer tube and are therefore driven up, to end up in the upper container. When up to 5 meters of core are drilled, the tubes are full, and the drill is brought back to the surface, the chips emptied from the upper container, and the ice core recovered from the inner tube.
Everything is controlled from the surface by a computer connected to the drill motor by way of electrical cables within the hauling metallic cable. The drilling is performed within a drilling fluid slightly denser than the ice (once we are in the ice, ca. 100 m depth), in order to prevent the hole from closing down from one year to the other (the ice deforms under its own weight and closes the hole!). It also prevents mechanical damage of the core by the drill, when the pressure of the ice around gets too big compared to the atmospheric pressure in the hole.
For intermediate depths, like at our Mass2Ant locations (300 m core, several centuries), we use a light-weighted version of the deep drilling system: the Eclipse drill (Canadian made). Because the quality of the cores was degrading under 100m depth last year, we will use a “wet drilling” version of the system, for the first time this year! Cross fingers and wait for the pictures of this year!
In the meantime, some pictures of last year! (photos: T.J. Young and Emmanuel Potvin)
The drill head with 3 knives, in rotation
Extracting the inner barrel (containing the core) from the outer barrel. In this light-weighted version, there is no dedicated chips chamber. The chips reaching the top of the spiral fall on top of the core in the inner barrel.
The drill trench and operators (Emmanuel and Etienne)
A good core
…and a bad (broken in) core!