The least dense crystalline form of water, topologically equivalent to the empty structure of sII clathrate hydrates.
Ice-sheet dynamics Sampling the surface of Taku Glacier in Alaska. There is increasingly dense firn between surface snow and blue glacier ice. An ice core is a vertical column through a glacier, sampling the layers that formed through an annual cycle of snowfall and melt.
At Summit Camp in Greenland, the depth is 77 m and the ice is years old; at Dome C in Antarctica the depth is 95 m and the age years.
The bubbles disappear and the ice becomes more transparent. Ice is lost at the edges of the glacier to icebergsor to summer melting, and the overall shape of the glacier does not change much with time.
These can be located using maps of the flow lines. These include soot, ash, and other types of particle from forest fires and volcanoes ; isotopes such as beryllium created by cosmic rays ; micrometeorites ; and pollen.
It can be up to about 20 m thick, and though it has scientific value for example, it may contain subglacial microbial populations it often does not retain stratigraphic information.
In polar areas, the sun is visible day and night during the local summer and invisible all winter. It can make some snow sublimateleaving the top inch or so less dense.
When the sun approaches its lowest point in the sky, the temperature drops and hoar frost forms on the top layer. Buried under the snow of following years, the coarse-grained hoar frost compresses into lighter layers than the winter snow. As a result, alternating bands of lighter and darker ice can be seen in an ice core.
Ice drilling Ice auger patented in ; the design is very similar to modern augers used for shallow drilling. 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 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 handleand some can be attached to handheld electric drills to power the rotation.
Below this depth, electromechanical or thermal drills are used. 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.
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 toxicityfor 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.
Newer fluids have been proposed, including new ester-based fluids, low-molecular weight dimethyl siloxane oils, fatty-acid estersand kerosene-based fluids mixed with foam-expansion agents.
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.
The core barrel is hoisted to the surface, and the core removed; the barrel is lowered again and reconnected to the drill assembly. This eliminates the need to disconnect and reconnect the pipes during a trip. These cable-suspended drills can be used for both shallow and deep holes; they require an anti-torque device, such as leaf-springs that press against the borehole, to prevent the drill assembly rotating around the drillhead as it cuts the core.
When the core is retrieved, the cuttings chamber is emptied for the next run. Some drills have been designed to retrieve a second annular core outside the central core, and in these drills the space between the two cores can be used for circulation.Ice core data for the antarctic and arctic used to determine historic weather conditions.
The North Greenland Eemian Ice Drilling - NEEM - is an international ice core research project aimed at retrieving an ice core from North-West Greenland (camp position °N °W) reaching back through the previous interglacial, the Eemian. Take home a pint of your favorite Ben & Jerry's ice cream flavor and enjoy with your family & friends, or just by yourself.
In , The United States Agency for International Development (USAID) funded the CHARIS project, or the Contribution to High Asia Runoff from Ice and Snow, at NSIDC .
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