An ice core is a core that is usually obtained by drilling into an ice sheet or glacier (the cryosphere). Ice cores are important climate archives ; by analyzing them, it is possible to obtain information about the climate of the past. This type of climate data acquisition is a very recent one, but at the same time one of the most important and precise methods known today.
The first attempt to take a sample from inside an ice sheet was made by the German polar explorer Ernst Sorge . At the station Eismitte in central Greenland he examined 1930/1931 the ice in a 15 m deep pit.
The first ice cores were obtained around 20 years later by three different international research teams: the Norwegian-British-Swedish Antarctic Expedition on the coast of Queen Maud Land from 1949 to 1952, the Juneau Icefield research project in Alaska and the French polar expeditions in Central Greenland. These ice cores from the early 1950s were around 100 m long and did not yet allow detailed analyzes.
The French climatologist and glaciologist Jean Jouzel mentions the international geophysical year 1957/1958 as the actual beginning of research using ice cores . A priority of the cooperation established this year was the extraction of deep cores from the polar ice sheets. In the fall of 1960, work began at Camp Century in northwest Greenland, which in six years drove the first uninterrupted ice core to the bedrock at a depth of 1,388 m. The drill was provided by the US Army's Cold Regions Research and Engineering Laboratory (CRREL) . Subsequently, it was possible in West Antarctica to use the same device to penetrate to a depth of 2164 m with a drill core near the Byrd station by 1968 .
In the early 1970s, the Greenland Ice Sheet Project (GISP) was born, led by a team from the University of Copenhagen . With a newly developed drill called Istuk , the project reached rock in three field campaigns, 1979 - 1981, at Dye 3 at a depth of 2038 m.
In April 1970, Soviet researchers began drilling in central East Antarctica near the Vostok station and in September of the same year they reached a depth of almost 507 m. It was there that the 3,623 m long Vostok ice core was finally extracted in 1998, which goes back 420,000 years. In February 2012 the project penetrated to Lake Vostok at a depth of 3769 m .
After initial drilling in the East Antarctic Adélieland , a French team carried out a 905 m deep hole at the Dome Concordia ( Dome Charlie ) station in central East Antarctica in the late 1970s . This location, on a crest of the ice sheet , made it easier to interpret the data obtained, because the accumulation of the glacier ice is vertical and shows hardly any lateral flow movements. It can thus be assumed that stored ice was also formed at this location. The Australian National Antarctic Research Expeditions drilled at Law Dome , in Wilkesland , East Antarctica , and at Dome Summit , where they reached the rock in 1993.
The Greenland drill cores obtained at Camp Century and Dye 3 showed a series of abrupt climatic fluctuations, but did not provide sufficient information about the last interglacial, the Eem warm period (115,000–126,000 years ago). The Danish paleoclimatologist Willi Dansgaard and his American colleague Wallace Broecker therefore initiated two new wells that were to take place at the same time and not far from each other. The European Greenland Ice Core Project ( GRIP ) took place in the years 1990-1992 from the highest point of the ice sheet and reached a depth of almost 3029 m, the American Greenland Ice Shield Project 2 located 28 km to the west ( GISP2 , 1990-1993 ) ended at 3054 m. Because of the folds of the ice over the uneven rock floor, layers more than 105,000 years old were found to be unreliable in both projects. This motivated the European deep well NGRIP (North Greenland Ice Core Project) about 200 km north over level rock in the years 1996-2003. It was possible to extract a 3,085 meter long core that goes back 123,000 years, i.e. to the middle of the last warm period before the present one, the Eem warm period.
To get information about the entire Eem, the North Greenland Eemian ice drilling project (NEEM, until July 2010) joined further north towards Camp Century . A sequence could be dated in this ice that goes 128,500 years into the past and thus also partially documents the change from the penultimate glacial (→ Saale Glaciation ) to the Eem.
The oldest drill core ever comes from the Antarctic from the European Project EPICA (European Project for Ice Coring in Antarctica) 2004. The ice at a depth of 3270.2 meters is around 900,000 years old and therefore contains information from more than eight ice age cycles.
From year to year a new layer of ice is deposited, a so-called annual layer. Thus, such a land ice sheet consists of many layers of ice lying on top of one another. Boreholes are typically carried out at the apex of an ice sheet, the so-called ice sheath , where mostly only vertical movements of the ice take place, so that disturbances from lateral flow movements are avoided.
Ice sheets are mainly found in Antarctica and Greenland . Some are over 3000 m thick and several hundred thousand years old. However, studies on the be glaciers of the polar and temperate regions and in the tropics performed, such as the Kilimanjaro ..
The deeper an annual layer lies in the ice, the older and thinner it is, as the weight of the layers above it compresses it and allows it to flow to the side. If you examine these individual layers, you can find out very precise information about specific years by counting the layers from above. The thickness of the individual annual layers gives an indication of the respective amount of precipitation .
Indications of events are examined both with regard to the point in time of their occurrence as well as a possibly existing temporal periodicity. Ice cores are always compared, i.e. In other words, it is checked whether an event can be found in another ice core, possibly obtained at a completely different location, which shows traces from the same time.
The ice contains small air bubbles that were trapped thousands of years ago. Trace gases are of interest , the proportion of which in the air is far less than 1%. The concentrations of carbon dioxide and methane are investigated , as these, in their role as greenhouse gases, had an important influence on the climate prevailing at the time. The analysis of the beryllium isotopes and carbon isotopes suggests solar activity at that time . A temperature analysis is carried out with the aid of the δ 18 O signal , among other things . In addition, the ratio of 2 H / 1 H ( deuterium / hydrogen ) is determined, which provides additional information on evaporation and condensation temperatures. The formation temperature of the precipitation and thus the air temperature in the polar regions of the earth can be reconstructed from ice cores over almost a million years. The ratio of 3 He to 4 He gives an indication of changes in the orientation of the earth's magnetic field . Analyzing the trapped 81 Kr, ice older than 50,000 years can be dated.
Trapped Solids Analysis
Dust content, ion and certain element concentrations allow conclusions to be drawn about the atmospheric circulation and the mean wind strengths prevailing at the time of origin.
Layers of dust found in ice cores can result from volcanic eruptions , which have occasionally triggered climate change. Dating the eruptions using ice cores is much more accurate than radiocarbon dating . The conductivity of the ice provides information about the amount of volcanic deposits from past eruptions. Petrographically , glass of volcanic origin is examined using electron microscopes and secondary ion mass spectrometers . The specific concentration of certain oxides and trace elements can then be compared with samples from volcanic eruptions in question and assigned. This not only examines with a temporal resolution of decades and centuries whether a volcanic eruption had climate-relevant consequences; conversely, it is also checked whether the effects of climate change - such as de-glaciation - had a verifiable influence on volcanic activity.
In addition, it can be determined whether the dust particles found are of terrestrial or extraterrestrial origin and whether they come from meteorite or micrometeorite impacts. We are looking for traces of iridium and osmium . The ratio of 187 Os / 186 Os decides whether the particles are of volcanic origin or are attributable to a meteorite impact. If the elements come from the earth's crust, this ratio is 400 to 1, for meteorites it is 3 to 1.
Other substances provide clues about the history of the environment and human influence. In the Greenland ice sheets, which in the period 1100 BC From AD 800 to AD 800, heavy metals such as lead, which were used in silver mining in Europe and the Mediterranean, were transported north by air currents and stored in the ice sheet. Lead concentrations dated to the exact year correspond closely to the economic history of European antiquity, such as the crises of the Roman Empire or the silver content of Roman coins . In the Arctic sea ice from 2014 and 2015, between 33 and 75,143 microplastic particles were found per liter of ice .
- Willi Dansgaard : Frozen Annals - Greenland Ice Sheet Research . 2005, ISBN 87-990078-0-0 ( ku.dk [PDF; 6.8 MB ]).
- J. Jouzel: A brief history of ice core science over the last 50 yr . In: Climate of the Past . November 2013, doi : 10.5194 / cp-9-2525-2013 .
- Chester C. Langway: The History of early Polar Ice Cores (= Technical Reports . TR-08-01). January 2008 ( ku.dk [PDF; 5.6 MB ]).
- Jean Jouzel: A brief history of ice core science over the last 50 yr . In: Climate of the Past . November 2013, doi : 10.5194 / cp-9-2525-2013 .
- Alfred Wegener Institute, EPICA project ( Memento from February 25, 2009 in the Internet Archive )
- University of Jena; M. Pirrung, M. Kunz-Pirrung, L. Viereck-Götte; Ice sheets and ice core archives ( Memento from June 11, 2007 in the Internet Archive )
- Background information on the GISP2 project website .
- GISP2 Notebook 2
- Joseph R. McConnell et al. a .: Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity . In: Proceedings of the National Academy of Sciences . May 29, 2018, doi : 10.1073 / pnas.1721818115 .
- Ilka Peeken, Sebastian Primpke, Birte Beyer, Julia Gütermann, Christian Katlein, Thomas Krumpen, Melanie Bergmann, Laura Hehemann & Gunnar Gerdts: Arctic sea ice is an important temporal sink and means of transport for microplastic . In: Nature Communications . 2018, doi : 10.1038 / s41467-018-03825-5 .