An ice core is a vertical column through a glacier, sampling the layers that formed through an annual cycle of snowfall and melt. 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 proportions of different oxygen and hydrogen isotopes provide information about ancient temperatures.
About Ice core in brief
An ice core is a vertical column through a glacier, sampling the layers that formed through an annual cycle of snowfall and melt. 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 proportions of different oxygen and hydrogen isotopes provide information about ancient temperatures. The air trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as carbon dioxide. Radioactive elements, either of natural origin or created by nuclear testing, can be used to date the layers of ice. Impurities in ice cores may depend on location. Coastal areas are more likely to include material of marine origin, such as sea salt ions. Greenland ice cores contain layers of wind-blown dust that correlate with cold, dry periods in the past, when cold deserts were scoured by wind. The lowest layer of a glacier called basal ice is frequently formed of subglacial meltwater that has refrozen and can be up to about 20 m thick. In polar areas such as Antarctica and central Greenland, the sun is never warm enough to cause melting, but the sun can still alter the snow. In the polar areas, the snow can still be refrozen, but often does not retain its scientific value as it does not often retain it for very long. The ice is lost at the edges of the glacier to icebergs, or to summer melting, and the overall shape of the glaciers does not change much with time.
It is desirable to drill deep ice cores at places where there is very little flow of the flow lines. These include Summit Camp in Greenland, where the ice is 230 years old; at Dome C in Antarctica the depth is 95 m and the age 2500 years. As further layers build up, the pressure increases, and at about 1500 m the crystal structure of the ice changes from hexagonal to cubic, allowing air molecules to move into the cubic crystals and form a clathrate. Two or three feet of snow may turn into less than a foot of ice, The weight above makes deeper layers ofice thin and flow outwards. These data can be combined to find the climate model that best fits all the available data, and it is important to find a model that fits the data all at once. 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. The deepest core reached 3769 m at Vostok Station, with the deepest core reaching 3769 in Antarctica. The depth at which this occurs varies with location, but in Greenland and the Antarctic it ranges from 64 m to 115 m. Because the age of the firn when it turns to ice varies a great deal. At a density of about 830 kgm3 it turned to ice, and is sealed into bubbles that capture the composition of the atmosphere at the time the ice formed.