Ледяные керны — керны, взятые из ледяного щита, чаще всего изо льда полярных ледяных шапок в Антарктике, Гренландии или высокогорных ледников. Так как лед образуется из нарастающих спрессованных слоев снега, нижележащие слои старше по отношению к вышележащим, ледяные керны содержат лед, сформировавшийся за многие годы. Свойства льда и кристаллических включений во льду могут быть использованы для воссоздания изменения климата в интервале формирования керна, обычно при помощи изотопного анализа. Они позволяют воссоздать изменение температуры и историю изменения атмосферных условий.^[1]

Ледяные керны содержат достаточную информацию о климате. Включения, попавшие в снег, остаются во льду, среди них может быть занесенная ветром пыль, пепел, пузырьки воздуха и радиоактивные вещества. Разнообразие климатических измерений шире чем у всех остальных природных инструментов датирования, таких как древесные кольца или донные отложения. Включения позволяют узнать температуру, объем океана, осадки, химические и физические условия в нижних слоях атмосферы, вулканическую активность, солнечную активность, продуктивность поверхности моря, опустынивание и лесные пожары.

Длина записи зависит от глубины ледяного керна и составляет от нескольких лет до 800 тыс. лет для кернов en:EPICA. Временное разрешение (самый короткий период времени, который может быть точно выделен) зависит от годового количества выпавшего снега, и уменьшается с глубиной так как лед спрессовывается под собственным весом. Верхние слои льда в керне соответствуют одному году или даже одному сезону. Чем глубже, тем слои тоньше и годовые слои перестают различаться.

Ледяные керны из различных мест могут быть использованы для воссоздания непрерывной и детальной картины климатических изменений на протяжении сотен тысяч лет, предоставляя информацию по широкому набору аспектов климата в каждый момент времени. Возможность сопоставить информацию из разных кернов по времени, делает ледяные керны могучим инструментом для палеоклиматических исследований.

Структуры ледяного покрова и кернов

Ледовый покров сформирован из снега. То что такой лед не тает летом, объясняется температурой, которая в данной местности редко превышает точку плавления. Во многих местах Антарктики температура воздуха всегда значительно ниже температуры замерзания воды. Если летняя температура начинает превышать температуру плавления, записи ледовых кернов серьезно разрушаются, вплоть до полной бесполезности, так как талая вода просачивается в снег.

Поверхностный слой состоит из снега во нескольких формах, с включениями воздуха. Продолжающийся накапливаться снег, в погребенных слоях прессуется и переходит в "зернистый лед", зернистый материал со структурой напоминающей сахар-песок. Воздушные включения остаются, и позволяют воздуху из окружающей среды циркулировать. С постепенным накоплением снега, зернистый лед уплотняется, и воздушные поры закрываются, оставляя часть воздуха внутри. Из-за того, что воздух некоторое время может циркулировать внутри снегового пласта, возраст льда и возраст газовых включений может отличаться, в зависимости от условий, даже на сотни лет. Различия в возрасте газа и льда, его включающего в 7 тыс. лет зафиксировано в ледниковом льду станции Восток ^[1]

С увеличением давления, на некоторой глубине "зернистый лед" переходит в лед. Эта глубина может составлять от нескольких метров до десятков, обычно до 100 метров (для Антарктических кернов). Ниже этого уровня материал заморожен, и представляет собой кристаллический лед. Последний может быть прозрачным или быть голубого цвета.

Слои могут визуально различаться в зернистом и обычном льду на значительных глубинах. На вершине ледника, где основный лед, имеет небольшую тенденцию к сползанию, создаются аккуратные слои с минимальными повреждениями. В местах, где нижние слои льда подвижны, глубокие слои могут иметь значительно различающиеся свойства и искажения. Керны, взятые возле основания ледника, часто сложны для анализа из-за изменений структуры и обычно включают составы из подстилающей поверхности.

Характеристики фирна

Слой пористого фирна в Антарктическом ледяном покрове находится на глубине от 50 до 150 м.^[1]. Что что намного меньше глубины ледников.

Воздух из атмосферы и фирнов медленно обменивается благодаря молекулярной диффузии через поры, из-за свойств газов перемещаться в сторону более низкой концентрации. Тепловая диффузия является причиной изотопного разделения в фирнах, когда здесь происходит быстрое изменение температуры, создающее разницу в изотопном составе захваченного воздушными пузырьками внутри льда в основании фирна. Этот газ двигается благодаря диффузии по фирне, но не выходит наружу, за исключением областей совсем рядом с поверхностью.

Ниже фирны находится зона в которой сезонные слои попеременно с открытыми и закрытыми порами. Эти слои уплотняются благодаря диффузии. Возраст газов быстро растет с глубиной слоев. Различные газы разделяются по пузырькам в процессе перехода фирнов (зернистого льда) в обычный лед.^[2]

Взятие проб

Керны извлекают отделением их от окружающего материала. Для достаточно мягкого материала, для отбора можно воспользоваться полой трубкой. С большой глубины керны берутся при помощи бурения твердого льда, а так же нижележащего каменного основания, при этом используются полые буры, с извлечением цилиндрического фрагмента прохода бурения вдоль керна.

При бурении, режущий аппарат находится на нижнем конце бурового ствола, который вырезает керн цилиндрической формы используя режущую кромку. Длина бурового ствола зависит от максимальной глубины отбора образцов кернов (6 м для GISP2 и Востока). Отбор длинных кернов, требует много циклов бурения - отбора керна, извлечения образца 4-6 м длины, подъем его на поверхность, извлечение из полого ствола, и подготовку к следующему бурению.

По причине того, что лед на большой глубине находится под большим давлением, и может быть поврежден, для кернов глубже чем 300 скважина может закрыться под действием давления окружающего льда. Скважину заполняют жидкостью для предохранения от обваливания. Жидкость, или смесь жидкостей, должна одновременно удовлетворять критерями высокого давления, низкой вязкости, устойчивости к замерзанию, а также быть безопасной в работе и безвредной к окружающей среда. Жидкость так же должна соответствовать ряду критериев, вытекающий, в частности из аналитических методов изучения ледяных кернов. Большое количество жидкостей и их смесей было опробовано в прошлом. С GISP2 (1990–1993) американскаская полярная программа использует однокомпонентную жидкостную систему, n-бутилацетата, но токситологически, огнеопасность, агрессивная природа растворителя, и долгосрочные пассивы n-бутилацетата вызывают ряд серьезных вопросов, относительно его дальнейшего применения. ЕС, а так же программа русских, ориентированна на двухкомпонентную систему для бурения, в которой жидкостью является углеводородная основа с низкой плотностью (коричневый керосин используется на станции Восток), которая доводится до плотности льда смешиванием с галогенированными углеводородами. Множество испытанных добавок в настоящий момент считаются слишком токсичными, или недопустимыми из-за необходимости соблюдать условия Монреальского протокола защиты озонового слоя.^[3] В апреле 1998 en:Devon Ice Cap фильтрованное en:lamp oil было использовано в качестве вспомогательной жидкости. На Девонском керне было отмечено, что ниже 150 м статиграфия была скрыта из-за микротрещин.^[4]

Core processing

Modern practice is to ensure that cores remain uncontaminated, since they are analysed for trace quantities of chemicals and isotopes. They are sealed in plastic bags after drilling and analysed in clean rooms.

The core is carefully extruded from the barrel; often facilities are designed to accommodate the entire length of the core on a horizontal surface. Drilling fluid will be cleaned off before the core is cut into 1-2 meter sections. Various measurements may be taken during preliminary core processing.

Current practices to avoid contamination of ice include:

• Keeping ice well below the freezing point.
  • At Greenland and Antarctic sites, temperature is maintained by having storage and work areas under the snow/ice surface.
  • At GISP2, cores were never allowed to rise above -15 °C, partly to prevent microcracks from forming and allowing present-day air to contaminate the fossil air trapped in the ice fabric, and partly to inhibit recrystallization of the ice structure.
• Wearing special clean suits over cold weather clothing.
• Mittens or gloves.
• Filtered respirators.
• Plastic bags, often polyethylene, around ice cores. Some drill barrels include a liner.
• Proper cleaning of tools and laboratory equipment.
• Use of laminar-flow bench to isolate core from room particulates.

For shipping, cores are packed in Styrofoam boxes protected by shock absorbing bubble-wrap.

Due to the many types of analysis done on core samples, sections of the core are scheduled for specific uses. After the core is ready for further analysis, each section is cut as required for tests. Some testing is done on site, other study will be done later, and a significant fraction of each core segment is reserved for archival storage for future needs.

Projects have used different core-processing strategies. Some projects have only done studies of physical properties in the field, while others have done significantly more study in the field. These differences are reflected in the core processing facilities.

Ice relaxation

Deep ice is under great pressure. When brought to the surface, there is a drastic change in pressure. Due to the internal pressure and varying composition, particularly bubbles, sometimes cores are very brittle and can break or shatter during handling. At Dome C, the first 1000 m were brittle ice. Siple dome encountered it from 400 to 1000 m. It has been found that allowing ice cores to rest for some time (sometimes for a year) makes them become much less brittle.

Decompression causes significant volume expansion (called relaxation) due to microcracking and the exsolving of enclathratized gases.^[5] Relaxation may last for months.^[6] During this time, ice cores are stored below -10 °C to prevent cracking due to expansion at higher temperatures. At drilling sites, a relaxation area is often built within existing ice at a depth which allows ice core storage at temperatures below -20 °C.

It has been observed that the internal structure of ice undergoes distinct changes during relaxation. Changes include much more pronounced cloudy bands and much higher density of "white patches" and bubbles.^[7]

Several techniques have been examined. Cores obtained by hot water drilling at Siple Dome in 1997–1998 underwent appreciably more relaxation than cores obtained with the PICO electro-mechanical drill. In addition, the fact that cores were allowed to remain at the surface at elevated temperature for several days likely promoted the onset of rapid relaxation.^[8]

Ice core data

Many materials can appear in an ice core. Layers can be measured in several ways to identify changes in composition. Small meteorites may be embedded in the ice. Volcanic eruptions leave identifiable ash layers. Dust in the core can be linked to increased desert area or wind speed.

Isotopic analysis of the ice in the core can be linked to temperature and global sea level variations. Analysis of the air contained in bubbles in the ice can reveal the palaeocomposition of the atmosphere, in particular CO₂ variations. There are great problems relating the dating of the included bubbles to the dating of the ice, since the bubbles only slowly "close off" after the ice has been deposited. Nonetheless, recent work has tended to show that during deglaciations CO₂ increases lags temperature increases by 600 +/- 400 years.^[2] Beryllium-10 concentrations are linked to cosmic ray intensity which can be a proxy for solar strength.

There may be an association between atmospheric nitrates in ice and solar activity. However, recently it was discovered that sunlight triggers chemical changes within top levels of firn which significantly alter the pore air composition. This raises levels of formaldehyde and NOx. Although the remaining levels of nitrates may indeed be indicators of solar activity, there is ongoing investigation of resulting and related effects of effects upon ice core data.^[9][10]

Core contamination

Some contamination has been detected in ice cores. The levels of lead on the outside of ice cores is much higher than on the inside.^[11] In ice from the Vostok core (Antarctica), the outer portion of the cores have up to 3 and 2 orders of magnitude higher bacterial density and dissolved organic carbon than the inner portion of the cores, respectively, as a result of drilling and handling.^[12]

Paleoatmospheric sampling

As porous snow consolidates into ice, the air within it is trapped in bubbles in the ice. This process continuously preserves samples of the atmosphere.^[13] In order to retrieve these natural samples the ice is ground at low temperatures, allowing the trapped air to escape. It is then condensed for analysis by gas chromatography or mass spectrometry, revealing gas concentrations and their isotopic composition respectively. Apart from the intrinsic importance of knowing relative gas concentrations (e.g. to estimate the extent of greenhouse warming), their isotopic composition can provide information on the sources of gases. For example CO₂ from fossil-fuel or biomass burning is relatively depleted in ¹³C. See Friedli et al., 1986.

Dating the air with respect to the ice it is trapped in is problematic. The consolidation of snow to ice necessary to trap the air takes place at depth (the 'trapping depth') once the pressure of overlying snow is great enough. Since air can freely diffuse from the overlying atmosphere throughout the upper unconsolidated layer (the 'firn'), trapped air is younger than the ice surrounding it.

Trapping depth varies with climatic conditions, so the air-ice age difference could vary between 2500 and 6000 years (Barnola et al., 1991). However, air from the overlying atmosphere may not mix uniformly throughout the firn (Battle et al., 1986) as earlier assumed, meaning estimates of the air-ice age difference could be less than imagined. Either way, this age difference is a critical uncertainty in dating ice-core air samples. In addition, gas movement would be different for various gases; for example, larger molecules would be unable to move at a different depth than smaller molecules so the ages of gases at a certain depth may be different. Some gases also have characteristics which affect their inclusion, such as helium not being trapped because it is soluble in ice.

In Law Dome ice cores, the trapping depth at DE08 was found to be 72 m where the age of the ice is 40±1 years; at DE08-2 to be 72 m depth and 40 years; and at DSS to be 66 m depth and 68 years.^[14]

Paleoatmospheric firn studies

At the South Pole, the firn-ice transition depth is at 122 m, with a CO₂ age of about 100 years. Gases involved in ozone depletion, CFCs, chlorocarbons, and bromocarbons, were measured in firn and levels were almost zero at around 1880 except for CH₃Br, which is known to have natural sources.^[15] Similar study of Greenland firn found that CFCs vanished at a depth of 69 m (CO₂ age of 1929).^[16]

Analysis of the Upper Fremont Glacier ice core showed large levels of chlorine-36 that definitely correspond to the production of that isotope during atmospheric testing of nuclear weapons. This result is interesting because the signal exists despite being on a glacier and undergoing the effects of thawing, refreezing, and associated meltwater percolation.^{[17] 36}Cl has also been detected in the Dye-3 ice core (Greenland)^[18], and in firn at Vostok.^[19]

Studies of gases in firn often involve estimates of changes in gases due to physical processes such as diffusion. However, it has been noted that there also are populations of bacteria in surface snow and firn at the South Pole, although this study has been challenged.^[20][21] It had previously been pointed out that anomalies in some trace gases may be explained as due to accumulation of in-situ metabolic trace gas byproducts.^[22]

Dating cores

Shallow cores, or the upper parts of cores in high-accumulation areas, can be dated exactly by counting individual layers, each representing a year. These layers may be visible, related to the nature of the ice; or they may be chemical, related to differential transport in different seasons; or they may be isotopic, reflecting the annual temperature signal (for example, snow from colder periods has less of the heavier isotopes of H and O). Deeper into the core the layers thin out due to ice flow and high pressure and eventually individual years cannot be distinguished. It may be possible to identify events such as nuclear bomb atmospheric testing's radioisotope layers in the upper levels, and ash layers corresponding to known volcanic eruptions. Volcanic eruptions may be detected by visible ash layers, acidic chemistry, or electrical resistance change. Some composition changes are detected by high-resolution scans of electrical resistance. Lower down the ages are reconstructed by modeling accumulation rate variations and ice flow.

Dating is a difficult task. Five different dating methods have been used for Vostok cores, with differences such as 300 years at 100 m depth, 600yr at 200 m, 7000yr at 400 m, 5000yr at 800 m, 6000yr at 1600 m, and 5000yr at 1934 m.^[23]

Different dating methods makes comparison and interpretation difficult. Matching peaks by visual examination of Moulton and Vostok ice cores suggests a time difference of about 10,000 years but proper interpretation requires knowing the reasons for the differences.^[24]

Ice core storage and transport

Ice cores are typically stored and transported in refrigerated ISO container systems. Due to the high value and the temperature-sensitive nature of the ice core samples, container systems with primary and back-up refrigeration units and generator sets are often used. Known as a Redundant Container System in the industry, the refrigeration unit and generator set automatically switches to its back-up in the case of a loss of performance or power to provide the ultimate peace of mind when shipping this valuable cargo.

Ice core sites

Ice cores have been taken from many locations around the world. Major efforts have taken place on Greenland and Antarctica.

Sites on Greenland are more susceptible to snow melt than those in Antarctica. In the Antarctic, areas around the Antarctic Peninsula and seas to the west have been found to be affected by ENSO effects. Both of these characteristics have been used to study such variations over long spans of time.^[25]

Greenland

The first to winter on the inland ice was J.P. Koch and Alfred Wegener in a hut they built on the ice in Northeast Greenland.^[3] Inside the hut they drilled to a depth of 25 m with an auger similar to an oversized corkscrew.

Station Eismitte

Eismitte means Ice-Center in German, and the campsite was located 402 kilometers (250 miles) from the coast at an estimated altitude of 3,000 meters (9,843 feet).

As a member of the Alfred Wegener Expedition to Eismitte in central Greenland from July 1930 to August 1931, Ernst Sorge hand-dug a 15 m deep pit adjacent to his beneath-the-surface snow cave. Sorge was the first to systematically and quantitatively study the near-surface snow/firn strata from inside his pit. His research validated the feasibility of measuring the preserved annual snow accumulation cycles, like measuring frozen precipitation in a rain gauge.^[4]

Camp VI

During 1950-1951 members of Expeditions Polaires Francaises (EPF) led by Paul Emile Victor reported boring two holes to depths of 126 and 150 m on the central Greenland inland ice at Camp VI and Station Central (Centrale).^[5] Camp VI is in the western part of Greenland on the EPF-EGIG line at an elevation of 1598 masl.

Station Centrale

The Station Centrale was not far from station Eismitte.^[3] Centrale is on a line between Milcent (70°18’N 45°35’W, 2410 masl) and Crête (71°7’N 37°19’W), at about (70°43'N 41°26'W), whereas Eismitte is at (71°10’N 39°56’W, ~3000 masl).

Site 2

In 1956, pre-International Geophysical Year (IGY) of 1957-58, a 10 cm diameter core using a rotary mechanical drill (US) to 305 m was recovered.^[4]

A second 10 cm diameter core was recovered in 1957 by the same drill rig to 411 m. A commercially modified, mechanical-rotary Failing-1500 rock-coring rig was used, fitted with special ice cutting bits.^[4]

Camp Century

Three cores were attempted at Camp Century in 1961, 1962, and again in 1963. The third hole was started in 1963 and reached 264 m. The 1963 hole was re-entered using the thermal drill (US) in 1964 and extended to 535 m. In mid-1965 the thermal drill was replaced with an electro-mechanical drill, 9.1 cm diameter, that reached the base of the ice sheet in July 1966 at 1387 m. The Camp Century, Greenland, (77°10’N 61°08’W, 1885 masl) ice core (cored from 1963–1966) is 1390 m deep and contains climatic oscillations with periods of 120, 940, and 13,000 years.^[3]

Another core in 1977 was drilled at Camp Century using a Shallow (Dane) drill type, 7.6 cm diameter, to 100 m.

North Site

At the North Site (75°46’N 42°27’W, 2870 masl) drilling began in 1972 using a SIPRE (US) drill type, 7.6 cm diameter to 25 m. The North Site was 500 km north of the EGIG line. At a depth of 6–7 m diffusion had obliterated some of the seasonal cycles.^[3]

North Central

The first core at North Central (74°37’N 39°36’W) was drilled in 1972 using a Shallow (Dane) drill type, 7.6 cm diameter to 100 m.

Crête

At Crête in central Greenland (71°7’N 37°19’W) drilling began in 1972 on the first core using a SIPRE (US) drill type, 7.6 cm diameter to 15 m.

The Crête core was drilled in central Greenland (1974) and reached a depth of 404.64 meters, extending back only about fifteen centuries.^[6] Annual cycle counting showed that the oldest layer was deposited in 534 AD.^[3]

The Crête 1984 ice cores consist of 8 short cores drilled in the 1984-85 field season as part of the post-GISP campaigns. Glaciological investigations were carried out in the field at eight core sites (A-H).^[7]

Milcent

"The first core drilled at Station Milcent in central Greenland covers the past 780 years."^[8] Milcent core was drilled at 70.3°N, 44.6°W, 2410 masl.^[8] The Milcent core (398 m) was 12.4 cm in diameter, using a Thermal (US) drill type, in 1973.

Dye 2

Drilling with a Shallow (Swiss) drill type at Dye 2 (66°23’N 46°11’W, 2338 masl) began in 1973. The core was 7.6 cm in diameter to a depth of 50 m. A second core to 101 m was 10.2 cm in diameter was drilled in 1974. An additional core at Dye 2 was drilled in 1977 using a Shallow (US) drill type, 7.6 cm diameter, to 84 m.

Summit Camp

The camp is located approximately 360 km from the east coast and 500 km from the west coast of Greenland at (Saattut, Uummannaq), and 200 km NNE of the historical ice sheet camp Eismitte. The closest town is Ittoqqortoormiit, 460 km ESE of the station. The station however is not part of Sermersooq municipality, but falls within the bounds of the Northeast Greenland National Park.

An initial core at Summit (71°17’N 37°56’W, 3212 masl) using a Shallow (Swiss) drill type was 7.6 cm in diameter for 31 m in 1974. Summit Camp, also Summit Station, is a year-round research station on the apex of the Greenland Ice Sheet. Its coordinates are variable, since the ice is moving. The coordinates provided here (72°34’45”N 38°27’26”W, 3212 masl) are as of 2006.

South Dome

The first core at South Dome (63°33’N 44°36’W, 2850 masl) used a Shallow (Swiss) drill type for a 7.6 cm diameter core to 80 m in 1975.

Hans Tausen (or Hans Tavsen)

The first GISP core drilled at Hans Tausen (82°30’N 38°20’W, 1270 masl) was in 1975 using a Shallow (Swiss) drill type, 7.6 cm diameter core to 60 m. The second core at Hans Tausen was drilled in 1976 using a Shallow (Dane) drill type, 7.6 cm diameter to 50 m. The drilling team reported that the drill was stuck in the drill hole and lost.

The Hans Tausen ice cap in Peary Land was drilled again with a new deep drill to 325 m. The ice core contained distinct melt layers all the way to bedrock indicating that Hans Tausen contains no ice from the glaciation; i.e., the world’s northernmost ice cap melted away during the post-glacial climatic optimum and was rebuilt when the climate got colder some 4000 years ago.^[3]

Camp III

The first core at Camp III (69°43’N 50°8’W) was drilled in 1977 using a Shallow (Swiss) drill type, 7.6 cm, to 49 m. The last core at Camp III was drilled in 1978 using a Shallow (Swiss) drill type, 7.6 cm diameter, 80 m depth.

Dye 3

The Greenland Ice Sheet Project (GISP) including Dye 3 was a decade-long project to drill 20^[9] ice cores in Greenland.

Renland

The Renland ice core from East Greenland apparently covers a full glacial cycle from the Holocene into the previous Eemian interglacial. It was drilled in 1985 to a length of 325 m.^[3][10] From the delta-profile, the Renland ice cap in the Scoresbysund Fiord has always been separated from the inland ice, yet all the delta-leaps revealed in the Camp Century 1963 core recurred in the Renland ice core.^[3]

GRIP/GISP

See main articles: GRIP, GISP

The GRIP and GISP cores, each about 3000 m long, were drilled by European and US teams respectively on the summit of Greenland. Their usable record stretches back more than 100,000 years into the last interglacial. They agree (in the climatic history recovered) to a few metres above bedrock. However, the lowest portion of these cores cannot be interpreted, probably due to disturbed flow close to the bedrock.^[26] There is evidence the GISP2 cores contain an increasing structural disturbance which casts suspicion on features lasting centuries or more in the bottom 10% of the ice sheet.^[27] The more recent NorthGRIP ice core provides a undisturbed record to approx. 123,000 years before present. The results indicate that Holocene climate has been remarkably stable and have confirmed the occurrence of rapid climatic variation during the last ice age.

NGRIP

The NGRIP drilling site is near the center of Holocene temperatures were.

NEEM

The North Greenland Eemian Ice Drilling (NEEM) site is located at 77°27’N 51°3.6’W, masl. Drilling started in June 2009. The ice at NEEM was expected to be 2545 m thick. On July 26, 2010, drilling reached bedrock at 2537.36 m.^[11]

Antarctica

For the list of ice cores visit IceReader web site

Plateau Station

Plateau Station is an inactive American research and Queen Maud Land traverse support base on the central Antarctic Plateau. The base was in continuous use until January 29, 1969. Ice core samples were made, but with mixed success.

Byrd Station

Marie Byrd Land formerly hosted the Operation Deep Freeze base Byrd Station (NBY), beginning in 1957, in the hinterland of Bakutis Coast. Byrd Station was the only major base in the interior of West Antarctica. In 1968, the first ice core to fully penetrate the Antarctic Ice Sheet was drilled here.

The Byrd 1968 core was 2164 m to bedrock and exhibited the post-glacial climatic optimum correlateably well with the Camp Century 1963 core from Greenland.^[3]

Dolleman Island

The British Antarctic Survey (BAS) has used Dolleman Island as ice core drilling site in 1976, 1986 and 1993.

Berkner Island

In the 1994/1995 field season the British Antarctic Survey, Alfred Wegener Institute and the Forschungsstelle für Physikalische Glaziologie of the University of Münster cooperated in a project drilling ice cores on the North and South Domes of Berkner Island.

Cape Roberts Project

Between 1997 and 1999 the international Cape Roberts Project (CRP) has recovered up to 1000 m long drill cores in the Ross Sea, Antarctica to reconstruct the glaciation history of Antarctica.

International Trans-Antarctic Scientific Expedition (ITASE)

The International Trans-Antarctic Scientific Expedition (ITASE) was created in 1990 with the purpose of studying climate change through research conducted in Antarctica. A 1990 meeting held in Grenoble, France, served as a site of discussion regarding efforts to study the surface and subsurface record of Antarctica’s ice cores.

Lake Vida

The lake gained widespread recognition in December 2002 when a research team, led by the University of Illinois at Chicago's Peter Doran, announced the discovery of 2,800 year old halophile microbes (primarily filamentous cyanobacteria) preserved in ice layer core samples drilled in 1996.^[12]

Vostok

As of 2003, the longest core drilled was at Vostok station. It reached back 420,000 years and revealed 4 past glacial cycles. Drilling stopped just above Lake Vostok. The Vostok core was not drilled at a summit, hence ice from deeper down has flowed from upslope; this slightly complicates dating and interpretation. Vostok core data are available.^[29]

EPICA/Dome C

The [13] Present-day annual average air temperature is -54.5 °C and snow accumulation 25 mm/y. Information about the core was first published in Nature on June 10, 2004. The core revealed 8 previous glacial cycles.

Although the major events recorded in the Vostok, EPICA, NGRIP, and GRIP during the last glacial period are present in all four cores some variation with depth (both shallower and deeper) occur between the Antarctic and Greenland cores.

Dome F

Two deep ice cores were drilled near the , altitude 3,810 m). The first drilling started in August 1995, reached a depth of 2503 m in December 1996 and covers a period back to 320,000 years. The second drilling started in 2003, was carried out during four subsequent austral summers from 2003/2004 until 2006/2007, and by then a depth of 3,035.22 m was reached. This core greatly extends the climatic record of the first core, and, according to a first, preliminary dating, it reaches back until 720,000 years.

WAIS Divide

The West Antarctic Ice Sheet Divide (WAIS Divide) Ice Core Drilling Project began drilling over the 2005 and 2006 seasons, drilling ice cores up to the depth of 300 m for the purposes of gas collection, other chemical applications, and to test the site for use with the Deep Ice Sheet Coring (DISC) Drill. Sampling with the DISC Drill will begin over the 2007 season and researchers and scientists expect that these new ice cores will provide data to establish a greenhouse gas record back over 40,000 years.

TALDICE

TAlos Dome Ice CorE Project is a new 1620 m deep ice core drilled at Talos Dome that provides a paleoclimate record covering at least the last 250,000 years. The TALDICE coring site (159°11'E 72°49'S; 2315 m a.s.l.; annual mean temperature -41°C) is located near the dome summit and is characterised by an annual snow accumulation rate of 80 mm water equivalent.^[14]

Non-polar cores

The non-polar ice caps, such as found on mountain tops, were traditionally ignored as serious places to drill ice cores because it was generally believed the ice would not be more than a few thousand years old, however since the 1970s ice has been found that is older, with clear chronological dating and climate signals going as far back as the beginning of the most recent ice age. Although polar cores have the clearest and longest chronological record, four-times or more as long, ice cores from tropical regions offer data and insights not available from polar cores and have been very influential in advancing understanding of the planets climate history and mechanisms.

Mountain ice cores have been retrieved in the Andes in South America, Mount Kilimanjaro in Africa, Tibet, various locations in the Himalayas, Alaska, Russia and elsewhere. Mountain ice cores are logistically very difficult to obtain. The drilling equipment must be carried by hand, organized as a mountaineering expedition with multiple stage camps, to altitudes upwards of 20,000 feet (helicopters are not safe), and the multi-ton ice cores must then be transported back down the mountain, all requiring mountaineering skills and equipment and logistics and working at low oxygen in extreme environments in remote third world countries. Scientists may stay at high altitude on the ice caps for up 20 to 50 days setting altitude endurance records that even professional climbers do not obtain. American scientist Lonnie Thompson has been pioneering this area since the 1970s, developing light-weight drilling equipment that can be carried by porters, solar-powered electricity, and a team of mountaineering-scientists. The ice core drilled in Guliya ice cap in western China in the 1990s reaches back to 760,000 years before the present — farther back than any other core at the time, though the EPICA core in Antarctica equalled that extreme in 2003.^[30]

Because glaciers are retreating rapidly worldwide, some important glaciers are now no longer scientifically viable for taking cores, and many more glacier sites will continue to be lost, the "Snows of Mount Kilimanjaro" (Hemingway) for example could be gone by 2015.^[15]

Upper Fremont Glacier

Ice core samples were taken from Upper Fremont Glacier in 1990-1991. These ice cores were analyzed for climatic changes as well as alterations of atmospheric chemicals. In 1998 an unbroken ice core sample of 164 m was taken from the glacier and subsequent analysis of the ice showed an abrupt change in the oxygen isotope ratio oxygen-18 to oxygen-16 in conjunction with the end of the Little Ice Age, a period of cooler global temperatures between the years 1550 and 1850. A linkage was established with a similar ice core study on the Quelccaya Ice Cap in Peru. This demonstrated the same changes in the oxygen isotope ratio during the same period.

Nevado Sajama

Ice cores from Sajama in Bolivia span ~25 ka and help present a high resolution temporal picture of the Late Glacial Stage and the Holocene climatic optimum.^[16]

Huascarán

Ice cores from Huascarán in Peru like those from Sajama span ~25 ka and help present a high resolution temporal picture of the Late Glacial Stage and the Holocene climatic optimum.^[16]

Quelccaya Ice Cap

Although the ice cores from Quelccaya ice cap only go back ~2 ka,^[16] others may go back ~5.2 ka. The Quelccaya ice cores correlate with those from the Upper Fremont Glacier.

Mount Kilimanjaro ice fields

Evidence for three periods of abrupt climate change in the Holocene climatic optimum have been recovered from six Kilimanjaro ice cores drilled in January and February 2000.^[17]

These cores provide a ~11.7 ka record of Holocene climate and environmental variability including three periods of abrupt climate change at ~8.3, ~5.2 and ~4 ka.^[17] These three periods correlate with similar events in the Greenland GRIP and GISP2 cores.^[17]

East Rongbuk Glacier

A shallow ice core drilled from the East Rongbuk glacier showed a dramatic increasing trend of black carbon concentrations in the ice stratigraphy since the 1990s.^[18]

See also

• Core drill
• Core sample in general from ocean floor, rocks and ice.
• Greenland ice cores
• Ice core brittle zone
• Jean Robert Petit
• Scientific drilling
• WAIS Divide Ice Core Drilling Project.

Notes

References