An ice core is a core sample from the accumulation of snow and ice over many years that have recrystallised and have trapped air bubbles from previous time periods. The composition of these samples, especially the presence of hydrogen and oxygen isotopes, provides a picture of the climate at the time.
Typically they are removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper, and the sample contains ice formed over a range of years. The properties of the ice or inclusions within the ice can then be used to reconstruct a climatic record over the age range of the core.
Ice cores contain an abundance of climate information. Inclusions in the snow of each year remain in the ice, such as wind-blown dust, ash, bubbles of atmospheric gas and radioactive substances. The variety of climatic proxies is greater than in any other natural recorder of climate, such as tree rings or sediment layers. These include (proxies for) temperature, ocean volume, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity, desert extent and forest fires.
The length of the record depends on the depth of the sample and varies from a few years up to 800 thousand years. The time resolution (i.e. the shortest time period which can be accurately distinguished) depends on the amount of annual snowfall, and reduces with depth as the ice compacts under the weight of layers accumulating on top of it. Upper layers of ice in a core correspond to a single year or sometimes a single season. Deeper into the ice the layers thin and annual layers become indistinguishable.
A sample from the right site can be used to reconstruct an uninterrupted and detailed climate record extending over hundreds of thousands of years, providing information on a wide variety of aspects of climate at each point in time. These are a powerful tool in paleoclimate research.
Ice Drilling Projects
The Greenland Ice Core Project (GRIP) was a multinational European research project, organised through the European Science Foundation.
The most dramatic finding from GRIP was that of the rapid climate changes in the last glacial period. These had been observed in previous cores, but GRIP confirmed their existence, their number, and the extreme rapidity of their onset in unprecedented detail. Such work has stimulated paleoclimatologists in other fields to see how global these events are and to look for causes.
North Greenland Ice Core Project (NGRIP) is a multinational research program, funded by participating institutions in Germany, Japan, Sweden, Switzerland, France, Belgium, Iceland and the US. Primary sponsor is the Danish Research Council. The Goal is to retrieve and analyze a 3080 m long sample drilled through the Greenland ice sheet at a place selected to give the longest reliable record.
Vostok Station is a Russian research station located near the South Geomagnetic Pole, at the center of the East Antarctic Ice Sheet. Vostok Station is located within the Australian Antarctic Territory.
In January 1998, the collaborative ice-drilling project between Russia, the United States, and France at the Russian Vostok station in East Antarctica yielded the deepest ice core ever recovered, reaching a depth of 3,623 m. Preliminary data indicate the Vostok ice-core record extends through four climate cycles, with ice slightly older than 400 thousand years. Although the Vostok core reached a depth of 3623 m the usable climatic information does not extend down this far. The very bottom of the core is ice refrozen from the waters of Lake Vostok and contains no climate information. The usual data sources give proxy information down to a depth of 3310 m or 414,000 years.
West Antarctic Ice Sheet Divide (WAIS Divide) Ice Core Project is a United States deep ice coring project in West Antarctica funded by the National Science Foundation (NSF) and is the second component to the larger WAISCORES initiative. The purpose of the WAIS Divide project is to collect a deep ice core from the flow divide in central West Antarctica in order to develop a unique series of interrelated climate, ice dynamics, and biologic records focused on understanding interactions among global earth systems.