Ice Core Dating
For a detailed look at how ice cores are recovered from Antarctica watch this video. 1. Why do scientists drill ice cores? 2. How does the drill work? 9. isotopes and known volcanic horizons can give a precise means of dating the layers. 3. Jan 9, How do ice cores work? | Layers dating of ice cores has been difficult, Uranium has been used to date the Dome C ice core from Antarctica. Jun 21, Dr Katja Riedel of NIWA explains how ice cores are dated. of greenhouse gases, which are increasing, work together with climate.
In order to get an intact climate record or archiveit is important that there is little melting of the snow surface during the summer months.
The problem with melt water is that it can flow downwards through the snowpack and mix up the chemicals of the different annual layers. Therefore when the scientists are working in the mountain glaciers of warmer, temperate regions, they like to get the highest, coldest ice they can find.
How deep are ice cores drilled?
Ice cores and climate change
The deepest ice cores have been drilled in the polar ice caps — Antarctica and Greenland, reaching a depth of over three kilometres.
Ice cores drilled into glaciers are usually much shallower, depending on the thickness of the glacier ice. Often they are no more than - meters deep. Sometimes it can be useful to drill a very short core of only a few meters, depending on the purpose of the research.
What has so far been discovered with ice core research? Polar regions give information related to the global climate. These have allowed scientists to make detailed investigations going back as far as years. Through the analysis of the air bubbles trapped within the ice, scientists have a window into previous conditions of the atmosphere. They have discovered that global temperatures are always related to the relative proportions of different gases — when conditions are warmer, the carbon dioxide and methane levels are higher.
At present the levels of these gases are much higher than they ever were in the last years and likely much longer due to the burning of fossil fuels. Another major discovery has been that climate change can occur very rapidly.
For example the transition from ice age to warm conditions in the past has occurred in perhaps less than ten years! In glaciated mountain areas away from the polar regions, ice cores give more localised information about climate history.
It is not possible to go so far back in time, and bubbles in the ice do not reliably trap the past atmospheric gases as well as they do in the polar ice caps.
However, these temperate ice cores are still extremely useful to help fill in details of the bigger climate picture. Many of the glaciers in mid or low latitude areas ie nearer to the equator are vulnerable to global warming, and glaciologists are urgently trying to retrieve such ice cores before they are affected by melting! What discoveries have our scientists made?
Ice cores have been retrieved from a number of coastal areas in Antarctica which have given detailed climate information. In collaboration with the University of Maine, ice cores were also retrieved from the Tasman Glacier in New Zealand in and three other glaciers in Mount Cook National park in What tests have to be made before the ice is drilled?
To find a site that is likely to have a high quality ice core record, some preliminary investigations are made: Topography Initially the surface topography of the glacier or ice sheet will give clues about the likely quality of the core.
Is the surface flat or dome shaped, without crevasses, and at a high enough altitude to ensure year round cold temperatures? Is it far enough away from cliff faces to avoid heat reflection from the rocks warming up the ice?
Is it in an area that is free of the scouring effect of prevailing winds that might have stripped some of the snow and ice off the surface?
Snow chemistry Once the scientists are satisfied with the general position and appearance of the site, they will then make an initial test of the snow chemistry. This is done by drilling or digging a few meters and taking many samples of the snow at regular intervals. The snow pit or drill core may also show a clearly defined summer layer from the previous year that will give some idea of the annual snowfall and the timescale that might be covered by a deeper ice core.
Radar At the same time, an ice penetrating radar will be used to survey the glacier or ice cap to find out the depth of the ice.
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This helps in planning the ideal drilling location. A high-frequency radar will also reveal the layer structure within the ice. This can be very useful to check that there is not too much ice distortion below the surface due to movement of the glacier. There are different types of radar that can be used.
They can be carried on foot, by ski, by skidoo or even flown over the ice in a plane, depending on the accessibility and the depth of the ice to be drilled. How does the drill work?
An ice core drill is essentially a hollow barrel with sharp teeth at one end which is rotated to cut down through the snow and ice. The oldest continuous ice core records to date extendyears in Greenland andyears in Antarctica.
Ice cores contain information about past temperature, and about many other aspects of the environment. Crucially, the ice encloses small bubbles of air that contain a sample of the atmosphere — from these it is possible to measure directly the past concentration of gases including carbon dioxide and methane in the atmosphere.
Measurements of CO2 from the Law Dome ice core 1 fall onto the line of annual average atmospheric measurements from South Pole 2 Greenhouse gases and the recent past Direct and continuous measurements of carbon dioxide CO2 in the atmosphere extend back only to the s.Antarctica's Ice Cores
Ice core measurements allow us to extend this way back into the past. In an Antarctic core Law Dome with a very high snowfall rate, it has been possible to measure concentrations in air from as recently as the s that is already enclosed in bubbles within the ice. Comparison with measurements made at South Pole station show that the ice core acts as a faithful recorder of atmospheric concentrations see Fig.
CO2 and CH4 over the last 1, years Antarctic ice cores show us that the concentration of CO2 was stable over the last millennium until the early 19th century. Measurements from older ice cores discussed below confirm that both the magnitude and rate of the recent increase are almost certainly unprecedented over the lastyears. CO2 concentration increased by the same amount, 20ppmv, in the last 10 years!
Methane CH4another important greenhouse gas, also shows a huge and unprecedented increase in concentration over the last two centuries. Its concentration is now much more than double its pre-industrial level. This is mainly due to the increase in emissions from sources such as rice fields, ruminant animals and landfills, that comes on top of natural emissions from wetlands and other sources.
This succession of events is well-known from other records, and the coldest periods in Antarctica are the times when we had ice ages. This is entirely consistent with the idea that temperature and CO2 are intimately linked, and each acts to amplify changes in the other what we call a positive feedback. Looking at the warming out of the last glacial period in detail, we can see how remarkably closely Antarctic temperature and CO2 tracked each other. In our modern era, of course, it is human emissions of CO2 that are expected to kick-start the sequence of events.
We see no examples in the ice core record of a major increase in CO2 that was not accompanied by an increase in temperature. Methane concentration also tracks the glacial-interglacial changes, probably because there were less wetlands in the colder, drier glacial periods.