An ice core is a core sample that was usually obtained through a hole in the ice sheet. Through the analysis of ice cores, it is possible to obtain information about past climate.
This type of climate data collection is a very young, but also one of the most important and most accurate methods that are known today. In this method, holes in the huge Landeisschilde the earth, in the cryosphere ( the ice of the earth), undertaken. The ice cores then promoted to day are thoroughly examined.
The idea that an ice core is an archive of climate information, going back to work carried out in the years 1930 to 1931 Greenland Expedition of Alfred Wegener. One of the scientists involved examined in a 15 meters deep pit dug the annual layers.
From year to year, a new layer of ice is from a so-called annual layer. Thus, there is such a Landeisschild of many superimposed layers of ice. Holes are typically set performed at the apex of these ice sheets, the so-called ice divide to encounter possible only vertical movement of the ice without interference by lateral flow movements.
Such huge ice sheets are mainly found in Antarctica and Greenland. Some have a thickness of about 3000 m and several hundred thousand years old. However, studies in polar and temperate climates and in the tropics are carried out on glaciers. An example of this is the glacier on Mount Kilimanjaro. The Alpine glaciers provide more information on the regional climate events, while holes in the polar ice sheets provide information on the global climate over the past year hundreds of thousands.
The first 100 -meter-long ice core was taken during a Norwegian -British- Swedish Antarctic Expedition, which took place in the years 1949 until 1952. The previously deepest core of the Greenland ice sheet resulted European deep drilling NGRIP (North Greenland Ice Core Project) in 2003. Here is a drilling depth of 3085 meters was reached, the oldest ice is 123,000 years old and comes from the last interglacial before the current of Eemian. The oldest core ever comes out of Antarctica from the European Project EPICA (European Project for Ice Coring in Antarctica ) 2004. The ice in 3270.2 meters depth is around 900,000 years old, and thus contains information from more than eight glacial cycles.
The deeper one years in the ice layer is, the older and thinner it is, because the weight of the overlying layers to compress and run through into the page. An examination of these individual layers, one can find very detailed information on specific years by counting down the layers from above. The thickness of the individual annual layers are there references to the respective rainfall.
A core sample is examined under compliance with scrupulous cleanliness. Evidence of events are examined in terms of both the time of their occurrence, as well as to an optional temporal periodicity out. Ice cores are always compared, that is, it is checked whether it is possible an event in another, possibly gained a completely different place ice core, which shows traces from the same time find.
In small air bubbles can be found even today air that has been trapped for thousands of years. Of interest are trace gases whose content in the air is far less than 1%. It examines the concentrations of carbon dioxide and methane, as these were an important influence on the then prevailing climate in its role as a greenhouse gas. The analysis of beryllium and carbon isotopes ( CO2 ) suggests the former solar activity. A temperature analysis is, among other things with the help of the δ18O signal. In addition, the ratio of 2H / 1H ( deuterium / hydrogen) is determined, which provides additional information on evaporation and condensation temperatures. In this way it is possible to reconstruct from ice cores, the formation temperature of the precipitate and thus the air temperature in the polar regions of the Earth over the past about one million years. The ratio of 3He to 4He are indications of changes in the direction of the geomagnetic field. The analysis of the trapped 81Kr is the only method which can be dated ice that is older than 50,000 years.
Analysis of trapped solids
Dust content, ion or certain element concentrations allow us to draw conclusions about the state of the atmospheric circulation and the prevailing at that time mean wind strength.
Dust layers found in ice cores sometimes come from volcanic eruptions, which were sometimes trigger climate change. A dating of eruptions using ice cores is significantly more accurate than radiocarbon dating. The conductivity of the ice provides information about the amount of volcanic deposits of past eruptions. Petro Graphically glass of volcanic origin with electron and secondary ion mass spectrometers is investigated. The specific concentration of certain oxides and trace elements can be compared and assigned with samples Candidate volcanic eruptions then. This is not only investigated with a time resolution of decades and centuries, if a volcanic eruption had climate-related consequences; shall also examine vice versa, whether the effects of climate change - such as a deglaciation - had a detectable influence on the volcanic activity.
In addition, it can be determined whether dust grains have found terrestrial or extraterrestrial origin and possibly originate from meteorite or micrometeorite impacts. We are looking for traces of iridium and osmium. The ratio of 187Os / 186Os decides whether the particles are of volcanic origin or attributable to a meteorite impact. Are the elements of the earth's crust, this ratio is 400 to 1, in meteorites, it is 3 to 1