page_title: Ice core
section_title: Coring
hierarchical_section_title: Ice core / Coring
caption_attribution_description: English: Retouched image of 1932 patent drawing of ice auger designed by F.W Brooks, Sr.
context_page_description: An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper, and an ice core contains ice formed over a range of years. Cores are drilled with hand augers or powered drills; they can reach depths of over two miles, and contain ice up to 800,000 years old.
  The physical properties of the ice and of material trapped in it can be used to reconstruct the climate over the age range of the core. The proportions of different oxygen and hydrogen isotopes provide information about ancient temperatures, and the air trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as carbon dioxide. Since heat flow in a large ice sheet is very slow, the borehole temperature is another indicator of temperature in the past. These data can be combined to find the climate model that best fits all the available data.
  Impurities in ice cores may depend on location. Coastal areas are more likely to include material of marine origin, such as sea salt ions.
context_section_description: Ice cores are collected by cutting around a cylinder of ice in a way that enables it to be brought to the surface.  Early cores were often collected with hand augers and they are still used for short holes. A design for ice core augers was patented in 1932 and they have changed little since.  An auger is essentially a cylinder with helical metal ribs (known as flights) wrapped around the outside, at the lower end of which are cutting blades.  Hand augers can be rotated by a T handle or a brace handle, and some can be attached to handheld electric drills to power the rotation.  With the aid of a tripod for lowering and raising the auger, cores up to 50 m deep can be retrieved, but the practical limit is about 30 m for engine-powered augers, and less for hand augers.  Below this depth, electromechanical or thermal drills are used.
  The cutting apparatus of a drill is on the bottom end of a drill barrel, the tube that surrounds the core as the drill cuts downward.  The cuttings (chips of ice cut away by the drill) must be drawn up the hole and disposed of or they will reduce the cutting efficiency of the drill.  They can be removed by compacting them into the walls of the hole or into the core, by air circulation (dry drilling), or by the use of a drilling fluid (wet drilling).  Dry drilling is limited to about 400 m depth, since below that point a hole would close up as the ice deforms from the weight of the ice above.
  Drilling fluids are chosen to balance the pressure so that the hole remains stable.  The fluid must have a low kinematic viscosity to reduce tripping time (the time taken to pull the drilling equipment out of the hole and return it to the bottom of the hole).  Since retrieval of each segment of core requires tripping, a slower speed of travel through the drilling fluid could add significant time to a project—a year or more for a deep hole.  The fluid must contaminate the ice as little as possible; it must have low toxicity, for safety and to minimize the effect on the environment; it must be available at a reasonable cost; and it must be relatively easy to transport.  Historically, there have been three main types of ice drilling fluids: two-component fluids based on kerosene-like products mixed with fluorocarbons to increase density; alcohol compounds, including aqueous ethylene glycol and ethanol solutions; and esters, including n-butyl acetate.  Newer fluids have been proposed, including new ester-based fluids, low-molecular weight dimethyl siloxane oils, fatty-acid esters, and kerosene-based fluids mixed with foam-expansion agents.
  
  Rotary drilling is the main method of drilling for minerals and it has also been used for ice drilling. It uses a string of drill pipe rotated from the top, and drilling fluid is pumped down through the pipe and back up around it.  The cuttings are removed from the fluid at the top of the hole and the fluid is then pumped back down.  This approach requires long trip times, since the entire drill string must be hoisted out of the hole, and each length of pipe must be separately disconnected, and then reconnected when the drill string is reinserted.  Along with the logistical difficulties associated with bringing heavy equipment to ice sheets, this makes traditional rotary drills unattractive.  In contrast, wireline drills allow the removal of the core barrel from the drill assembly while it is still at the bottom of the borehole.  The core barrel is hoisted to the surface, and the core removed; the barrel is lowered again and reconnected to the drill assembly.  Another alternative is flexible drill-stem rigs, in which the drill string is flexible enough to be coiled when at the surface.  This eliminates the need to disconnect and reconnect the pipes during a trip.
  The need for a string of drillpipe that extends from the surface to the bottom of the borehole can be eliminated by suspending the entire downhole assembly on an armoured cable that conveys power to the downhole motor.  These cable-suspended drills can be used for both shallow and deep holes; they require an anti-torq
caption: Ice auger patented in 1932; the design is very similar to modern augers used for shallow drilling.[10]
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