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It is not uncommon to read that ice cores from the polar regions contain records of climatic change from the distant past. Research teams from the United States, the Soviet Union, Denmark, and France have bored holes over a mile deep into the ice near the poles and removed samples for analysis in their laboratories. Based on flow models, the variation of oxygen isotopes, the concentration of carbon dioxide in trapped air bubbles, the presence of oxygen isotopes, acid concentrations, and particulates, they believe the lowest layers of the ice sheets were laid down over , years ago. Annual oscillations of such quantities are often evident in the record. Are these records in the ice legitimate? Do they cause a problem for the recent-creation model of earth history? What are we to make of these data?

Dating the ice becomes harder with depth. Usually multiple methods are used to improve accuracy. Common global stratigraphic markers are palaeo-events that occur worldwide synchronously, and can allow wiggle-matching between ice cores and other palaeo archives e.

For the ice matrix, these global stratigraphic markers can include spikes in volcanic ash each volcanic eruption has a unique chemical signatureor volcanic sulfate spikes.

For the gas phase, methane, and oxygen isotopic ratio of O 2 have been used Lemieux-Dudon et al. Uranium has been used to date the Dome C ice core from Antarctica.

How are ice cores dated?

Dust is present in ice cores, and it contains Uranium. The decay of U to U from dust in the ice matrix can be used to provide an additional core chronology.

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Beryillium has also been used to date ice cores. Ice cores are expensive to collect, house and keep. They must be stored continuously at a specific temperature. The American National Ice Core Laboratory provides some information on how they store and keep ice cores. When ice cores are analysed, they may be cut or sectioned, with half the sample remaining as an archive.

As the ice must be melted for analysis, the sample is usually destroyed during analysis. Lemieux-Dudon B, et al. Consistent dating for Antarctic and Greenland ice cores. Quaternary Science Reviews 29, Mulvaney R, et al. Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history. A difficulty in ice core dating is that gases can diffuse through firn, so the ice at a given depth may be substantially older than the gases trapped in it.

As a result, there are two chronologies for a given ice core: one for the ice, and one for the trapped gases.

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To determine the relationship between the two, models have been developed for the depth at which gases are trapped for a given location, but their predictions have not always proved reliable. The density and size of the bubbles trapped in ice provide an indication of crystal size at the time they formed.

The size of a crystal is related to its growth rate, which in turn depends on the temperature, so the properties of the bubbles can be combined with information on accumulation rates and firn density to calculate the temperature when the firn formed. Radiocarbon dating can be used on the carbon in trapped CO 2.

The CO 2 can be isolated by subliming the ice in a vacuum, keeping the temperature low enough to avoid the loess giving up any carbon. The results have to be corrected for the presence of 14 C produced directly in the ice by cosmic rays, and the amount of correction depends strongly on the location of the ice core. Corrections for 14 C produced by nuclear testing have much less impact on the results.

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The very small quantities typically found require at least g of ice to be used, limiting the ability of the technique to precisely assign an age to core depths. Timescales for ice cores from the same hemisphere can usually be synchronised using layers that include material from volcanic events.

It is more difficult to connect the timescales in different hemispheres. The Laschamp eventa geomagnetic reversal about 40, years ago, can be identified in cores; [45] [46] away from that point, measurements of gases such as CH 4 methane can be used to connect the chronology of a Greenland core for example with an Antarctic core.

This approach was developed in and has since been turned into a software tool, DatIce. The boundary between the Pleistocene and the Holoceneabout 11, years ago, is now formally defined with reference to data on Greenland ice cores.

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Formal definitions of stratigraphic boundaries allow scientists in different locations to correlate their findings. These often involve fossil records, which are not present in ice cores, but cores have extremely precise palaeoclimatic information that can be correlated with other climate proxies.

The dating of ice sheets has proved to be a key element in providing dates for palaeoclimatic records. Cores show visible layers, which correspond to annual snowfall at the core site. If a pair of pits is dug in fresh snow with a thin wall between them and one of the pits is roofed over, an observer in the roofed pit will see the layers revealed by sunlight shining through.

A six-foot pit may show anything from less than a year of snow to several years of snow, depending on the location. Poles left in the snow from year to year show the amount of accumulated snow each year, and this can be used to verify that the visible layer in a snow pit corresponds to a single year's snowfall. In central Greenland a typical year might produce two or three feet of winter snow, plus a few inches of summer snow.

When this turns to ice, the two layers will make up no more than a foot of ice. The layers corresponding to the summer snow will contain bigger bubbles than the winter layers, so the alternating layers remain visible, which makes it possible to count down a core and determine the age of each layer. Dust layers may now become visible. Ice from Greenland cores contains dust carried by wind; the dust appears most strongly in late winter, and appears as cloudy grey layers.

These layers are stronger and easier to see at times in the past when the earth's climate was cold, dry, and windy. Any method of counting layers eventually runs into difficulties as the flow of the ice causes the layers to become thinner and harder to see with increasing depth. When there is summer melting, the melted snow refreezes lower in the snow and firn, and the resulting layer of ice has very few bubbles so is easy to recognise in a visual examination of a core.

MF calculations are averaged over multiple sites or long time periods in order to smooth the data. Plots of MF data over time reveal variations in the climate, and have shown that since the late 20th century melting rates have been increasing.

Hence core, ice new The Cs and activity ? total using core ice the of dating age radioactive for used and intervals m 1 about in composited were chips ice scraped The measurements activity ? total for collected were core ice the of m 30 upper the in samples Thirty-five. Regions polar the and glaciers mountain high from come records. Aug 21,   Scientists working in the Allen Hills region of Antarctica have drilled the oldest ice core ever. Dating back an estimated million years, this ice sample is more than million years older. Other ways of dating ice cores include geochemisty, wiggle matching of ice core records to insolation time series (Lemieux-Dudon et al. ), layers of volcanic ash (tephra) (Vinther et al., ), electrical conductivity, and using numerical flow models to understand age-depth relationships (Mulvaney et al., ), combined with firn.

In addition to manual inspection and logging of features identified in a visual inspection, cores can be optically scanned so that a digital visual record is available. This requires the core to be cut lengthwise, so that a flat surface is created.

The isotopic composition of the oxygen in a core can be used to model the temperature history of the ice sheet. Oxygen has three stable isotopes, 16 O17 O and 18 O.

The clarity of the annual signal in the isotope data makes counting of annual layers in ? 18 O data one of the most accurate ways of dating ice cores. At least the upper parts of most Greenland ice cores have therefore been dated from thousands of ? 18 O samples that have been individually cut from the ice core, packed, and measured in a mass spectrometer (read more about the measurements here). Aug 15,   Record-shattering million-year-old ice core reveals start of the ice ages. By Paul Voosen Aug. 15, , PM. Scientists announced today that a . Ice Core Dating. By sampling at very fine intervals down the ice core, and provided that each annual layer of snow is thick enough, several samples from each year may be measured for the different chemical properties. It has already been seen that the delta value is related to .

At lower temperatures, the difference is more pronounced. If the site has experienced significant melting in the past, the borehole will no longer preserve an accurate temperature record.

Hydrogen ratios can also be used to calculate a temperature history. Deuterium 2 Hor D is heavier than hydrogen 1 H and makes water more likely to condense and less likely to evaporate. It was once thought that this meant it was unnecessary to measure both ratios in a given core, but in Merlivat and Jouzel showed that the deuterium excess reflects the temperature, relative humidity, and wind speed of the ocean where the moisture originated.

Since then it has been customary to measure both. Water isotope records, analyzed in cores from Camp Century and Dye 3 in Greenland, were instrumental in the discovery of Dansgaard-Oeschger events -rapid warming at the onset of an interglacialfollowed by slower cooling.

Combining this information with records of carbon dioxide levels, also obtained from ice cores, provides information about the mechanisms behind changes in CO 2 over time. It was understood in the s that analyzing the air trapped in ice cores would provide useful information on the paleoatmospherebut it was not until the late s that a reliable extraction method was developed. Further research has demonstrated a reliable correlation between CO 2 levels and the temperature calculated from ice isotope data.

Because CH 4 methane is produced in lakes and wetlandsthe amount in the atmosphere is correlated with the strength of monsoonswhich are in turn correlated with the strength of low-latitude summer insolation. Since insolation depends on orbital cyclesfor which a timescale is available from other sources, CH 4 can be used to determine the relationship between core depth and age. This means that the trapped air retains, in the ratio of O 2 to N 2a record of the summer insolation, and hence combining this data with orbital cycle data establishes an ice core dating scheme.

Diffusion within the firn layer causes other changes that can be measured. Gravity causes heavier molecules to be enriched at the bottom of a gas column, with the amount of enrichment depending on the difference in mass between the molecules.

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Colder temperatures cause heavier molecules to be more enriched at the bottom of a column. Greenland cores, during times of climatic transition, may show excess CO2 in air bubbles when analysed, due to CO2 production by acidic and alkaline impurities [81]. Summer snow in Greenland contains some sea salt, blown from the surrounding waters; there is less of it in winter, when much of the sea surface is covered by pack ice.

Similarly, hydrogen peroxide appears only in summer snow because its production in the atmosphere requires sunlight. These seasonal changes can be detected because they lead to changes in the electrical conductivity of the ice. Placing two electrodes with a high voltage between them on the surface of the ice core gives a measurement of the conductivity at that point. Dragging them down the length of the core, and recording the conductivity at each point, gives a graph that shows an annual periodicity.

Such graphs also identify chemical changes caused by non-seasonal events such as forest fires and major volcanic eruptions. When a known volcanic event, such as the eruption of Laki in Iceland incan be identified in the ice core record, it provides a cross-check on the age determined by layer counting.

If the date of the eruption is not known, but it can be identified in multiple cores, then dating the ice can in turn give a date for the eruption, which can then be used as a reference layer. Many other elements and molecules have been detected in ice cores.

Ice core age dating

Both hydrogen peroxide H 2 O 2 and formaldehyde HCHO have been studied, along with organic molecules such as carbon black that are linked to vegetation emissions and forest fires. Some of the deposited chemical species may interact with the ice, so what is detected in an ice core is not necessarily what was originally deposited. Another complication is that in areas with low accumulation rates, deposition from fog can increase the concentration in the snow, sometimes to the point where the atmospheric concentration could be overestimated by a factor of two.

Galactic cosmic rays produce 10 Be in the atmosphere at a rate that depends on the solar magnetic field. The strength of the field is related to the intensity of solar radiationso the level of 10 Be in the atmosphere is a proxy for climate. Accelerator mass spectrometry can detect the low levels of 10 Be in ice cores, about 10, atoms in a gram of ice, and these can be used to provide long-term records of solar activity.

Meteorites and micrometeorites that land on polar ice are sometimes concentrated by local environmental processes. For example, there are places in Antarctica where winds evaporate surface ice, concentrating the solids that are left behind, including meteorites. Meltwater ponds can also contain meteorites.

Ice Core Drilling Projects

At the South Pole Stationice in a well is melted to provide a water supply, leaving micrometeorites behind. These have been collected by a robotic "vacuum cleaner" and examined, leading to improved estimates of their flux and mass distribution. The well becomes about 10 m deeper each year, so micrometeorites collected in a given year are about years older than those from the previous year. It provides information on changes in vegetation.

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In addition to the impurities in a core and the isotopic composition of the water, the physical properties of the ice are examined. Features such as crystal size and axis orientation can reveal the history of ice flow patterns in the ice sheet.

The crystal size can also be used to determine dates, though only in shallow cores.

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In an Louis Agassiz drilled holes in the Unteraargletscher in the Alps ; these were drilled with iron rods and did not produce cores. The first scientist to create a snow sampling tool was James E. Churchdescribed by Pavel Talalay as "the father of modern snow surveying".

Nothing in the ice-core data from either Greenland or Antarctica requires the earth to be of great age. In fact, there are good reasons to believe that the ice cores are revealing important information about conditions following the Flood of Genesis and the recent formation of thick ice sheets. From the data gathered from the Vostok ice-core indicates that the minimum age of the earth is , +- 15, years. Furthermore there exists approximately 33of additional ice below the core sample which would hold a disproportionate number of years due to thinning of the ice layers under the tremendous pressure of the ice above it. Jul 30,   The dating of NorthGRIP The ice core is believed to contain ice that is , years old at the bottom.4 This date was obtained by matching the oxygen isotope ratio down this core with other ice cores in Greenland. The oxygen isotope ratio is a general measure of temperature, but many other variables can affect the Michael J. Oard.

They are simply pushed into the snow and rotated by hand. The first systematic study of snow and firn layers was by Ernst Sorge, who was part of the Alfred Wegener Expedition to central Greenland in - Core quality was poor, but some scientific work was done on the retrieved ice.

The International Geophysical Year - saw increased glaciology research around the world, with one of the high priority research targets being deep cores in polar regions. SIPRE conducted pilot drilling trials in to m and to m at Site 2 in Greenland; the second core, with the benefit of the previous year's drilling experience, was retrieved in much better condition, with fewer gaps. Soviet ice drilling projects began in the s, in Franz Josef Lan the UralsNovaya Zemlyaand at Mirny and Vostok in the Antarctic; not all these early holes retrieved cores.

The Dome C core had very low accumulation rates, which mean that the climate record extended a long way; by the end of the project the usable data extended toyears ago.

Incores were retrieved from the Allan Hills in Antarctica in an area where old ice lay near the surface. The cores were dated by potassium-argon dating; traditional ice core dating is not possible as not all layers were present. The oldest core was found to include ice from 2. Inscientific discussions began which resulted in the Greenland Ice Sheet Project GISPa multinational investigation into the Greenland ice sheet that lasted until A location in north-central Greenland was selected as ideal, but financial constraints forced the group to drill at Dye 3 instead, beginning in The hole did not reach bedrock, but terminated at a subglacial river.

The core provided climatic data back toyears ago, which covered part of the last interglacial period. Ice cores have been drilled at locations away from the poles, notably in the Himalayas and the Andes.

IPICS International Partnerships in Ice Core Sciences has produced a series of white papers outlining future challenges and scientific goals for the ice core science community. These include plans to:.

From Wikipedia, the free encyclopedia. Cylindrical sample drilled from an ice sheet. See also: Ice-sheet dynamics. See also: Ice drilling. Sliver of Antarctic ice showing trapped bubbles. See also: History of scientific ice drilling.

Paleoclimatology: Reconstructing Climates of the Quaternary. Amsterdam: Academic Press. Cheltenham, UK: Stanley Thornes. In Blais, Jules M. Dordrecht, Netherlands: Springer. Retrieved 3 June Annals of Glaciology. East Greenland Ice Core Project.

Retrieved 17 June Archived from the original on 28 June The New Yorker. National Ice Core Laboratory. Archived from the original on 4 May Retrieved 21 May Eos Trans AGU. Memoirs of National Institute of Polar Research 49 : Archived from the original on 14 July Climate of the Past.

The Cryosphere. ScienceX network. Retrieved 29 May Encyclopedia of Quaternary Science. Amsterdam: Elsevier. EGU General Assembly Vienna, Austria. Retrieved 5 September Journal of Quaternary Science. Archived from the original on 13 February Quaternary Science Reviews. Global and Planetary Climate Change. Retrieved 20 May Centre for Ice and Climate. Retrieved 25 May Scientific American. Proceedings of the National Academy of Sciences. Archived from the original on 8 August Retrieved 2 June David Climate Change and Climate Modeling.

Cambridge: Cambridge University Press. Atmospheric Chemistry and Physics. Archived from the original on 13 September Retrieved 14 September

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