In Greenland, a sequence of collaborative projects began in the 1970s with the Greenland Ice Sheet Project; there have been multiple follow-up projects, with the most recent, the East Greenland Ice-Core Project, expected to complete a deep core in east Greenland in 2020.Because the rate of snowfall varies from site to site, the age of the firn when it turns to ice varies a great deal.It can make some snow sublimate, leaving the top inch or so less dense.
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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.
Soviet ice drilling projects in Antarctica include decades of work at Vostok Station, with the deepest core reaching 3769 m.
Numerous other deep cores in the Antarctic have been completed over the years, including the West Antarctic Ice Sheet project, and cores managed by the British Antarctic Survey and the International Trans-Antarctic Scientific Expedition.
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.
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).Ice is lost at the edges of the glacier to icebergs, or to summer melting, and the overall shape of the glacier does not change much with time.Impurities in the ice provide information on the environment from when they were deposited.These include soot, ash, and other types of particle from forest fires and volcanoes; isotopes such as beryllium-10 created by cosmic rays; micrometeorites; and pollen.The lowest layer of a glacier, called basal ice, is frequently formed of subglacial meltwater that has refrozen.Cores are drilled with hand augers (for shallow holes) or powered drills; they can reach depths of over two miles (3.2 km), and contain ice up to 800,000 years old.