Greenland ice cores

The Greenland ice cores are samplings typically removed from the ice sheet of Greenland by coring into the ice.
Ice sheet
An 'ice sheet' is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km (20,000 mile ), thus also known as a 'continental glacier'. The only current ice sheets are in Antarctica and Greenland.
Greenland ice sheet
The Greenland ice sheet occupies about 82% of the surface of Greenland, and if melted would cause sea levels to rise by 7.2 metres. The ice sheet is almost 2,400 kilometers long in a north-south direction, and its greatest width is 1,100 kilometers at a latitude of 77°N, near its northern margin.
The ice surface reaches its greatest altitude on two north-south elongated domes, or ridges. The southern dome reaches almost 3,000 metres at latitudes 63°-65°N; the northern dome reaches about 3,290 metres at about latitude 72°N. The crests of both domes are displaced east of the centre line of Greenland. The unconfined ice sheet does not reach the sea along a broad front anywhere in Greenland, so that no large ice shelves occur.
Ice core
An ice core is a core sample from the accumulation of snow and ice. As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice core contains ice formed over a range of years. The composition of these ice cores, especially the presence of hydrogen and oxygen isotopes, provides a picture of the climate at the time. Ice cores contain an abundance of climate information.
Ice core site
Major efforts have taken place on Greenland, where the sites are more susceptible to snow melt than those in Antarctica. Ice cores have been taken from many locations around Greenland.
After the Camp Century deep drilling, a search began for the most favorable location in Greenland for another deep core drilling. The most important criteria are
# no surface melting that could change the chemical composition,
# a simple ice flow pattern ensuring undisturbed stratification at great depths, and
# seasonal δ-cycles preserved for dating by counting annual layers. Inside the hut they drilled to a depth of 25 m with an auger similar to an oversized corkscrew. They measured temperature versus depth and time throughout the winter. His research validated the feasibility of measuring the preserved annual snow accumulation cycles, like measuring frozen precipitation in a rain gauge, at least for the upper surface layers.
Centrale 1951
During 1950-1951 members of Expeditions Polaires Francaises (EPF) reported boring two holes to depths of 126 and 150 m on the central Greenland inland ice at Camp VI and Station Central (Centrale), respectively. Station Centrale is not far from station Eismitte.
At right is an image of the first climate curve from an ice core, specifically the Camp Century 1963 ice core to 1390 m. Results from the analysis of the Camp Century ice core show that past climate conditions can be derived from ice cores. The graph shows the amount of heavy isotopes (given as a δ O value) as a function of depth and age along the ice core. O is an oxygen isotope. Low δ O values are associated with low temperatures and vice versa, and the shift of δ O values at 11-1200 m / ~11,000 years is the shift from the glacial to the current interglacial. Different episodes of past climate are identified (red and black labels): the 1930 climatic optimum, the Little ice age, the Medieval climate optimum (Medieval warmth), and the Holocene climatic optimum (Post glacial optimum). Probably the most important outcome from the analysis of the Camp Century ice core is the demonstration that ice core drilling and the oxygen isotope analysis are viable ways of reconstructing past climate.
Another core in 1977 is drilled at Camp Century using a Shallow (Danish) drill type, 7.6 cm diameter, to 100 m.
Dye 3 ice core
'Dye 3' is an ice core site and previously part of the Distant Early Warning (DEW) line, located at , 2480 masl, in Greenland.
As part of the Greenland Ice Sheet Project (GISP), annual field expeditions are carried out to drill intermediate depth cores at various locations on the ice sheet. A number of these cores are from Dye 3, designated here by 'Dye 3' followed by the year drilling began:
# Dye 3 1971 to a depth of 372 m,
# Dye 3 1973, an intermediate drilling to c. 390 m, some 740 seasonal δ cycles are counted, indicating that the core reaches back to 1231 AD, as melt water seeps through the porous snow, it refreezes somewhere in the cold firn and disturbs the layer sequence,
# Dye 3 1975 to 95 m,
# Dye 3 1976 to 93 m,
# Dye 3 1978 to 90 m, measurements of and in firn samples spanning the period 1895-1978 are from the Dye 3 1978 core down to 70 m,
# Dye 3 1979 to bedrock at 2038 m, the borehole is 41.5 km east of the local ice divide of the south Greenland ice sheet, and
# Dye 3 1988 to an intermediate depth, by a glaciological team led by Ellen Mosley-Thompson.

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