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About Ice Cores - FAQs

Find out why ice core research is so important for our understanding of climate change and how we drill and analyse the ice cores. For a detailed look at how ice cores are recovered from Antarctica watch this video.

1. Why do scientists drill ice cores?
2. What makes ice cores so useful for climate research?
3. Where do you drill them?
4. How deep are the ice cores drilled?
5. What has so far been discovered with ice core research?
6. What discoveries have our scientists made?
7. What tests have to be made before the ice is drilled?
8. How does the drill work?
9. What do you do next with the ice cores?
10. How do you analyse the ice?
11. What sort of information can be found out by the analyses?


1. Why do scientists drill ice cores?

icy mountains

Ice cores are drilled in polar regions or high mountain areas by scientists who want to learn about the Earth’s climate. By studying patterns in the way the climate has changed in the past it is possible to follow trends that show likely climate changes in the future.

2. What makes ice cores so useful for climate research?

As the snow accumulates each year it builds up into a sequence of layers that contain a surprising amount of information. For example there may well be evidence for the prevailing wind direction and strength, total annual precipitation and average temperatures. Air pollutants such as soot particles and a wide variety of chemicals are also trapped in the ice layers as well as dust from volcanic eruptions and sandstorms.

Apart from direct measurements using weather instruments like thermometers, and anemometers (which have only been systematically used on a global scale for about 150 years), ice cores are one of the best ways we have of getting detailed records of past weather patterns.

Usually the winter snow accumulation is seen as a thicker, lighter coloured layer compared to the thinner, darker summer layer. By counting down the layers, it is often possible to calculate the number of years represented in a particular ice core. In addition, other dating methods using radioactive isotopes and known volcanic horizons can give a precise means of dating the layers.

3. Where do you drill them?

drilling ice cores

The ideal place to drill an ice core is an ice cap or glacier which has very little sideways movement of the ice over time. If there is a lot of snow accumulation each year, the record will provide a lot of detail. A slow accumulation area such as in central Antarctica or Greenland will provide a very long record compiled of thin annual layers.

In order to get an intact climate record (or archive), it 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.

4. How deep are ice cores drilled?

scientists drilling ice core

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 100 - 200 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.

5. 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 800 000 years. They have shown that the Earth as been through a series of climate cycles – ice ages and warmer interglacials – that relate to gradual shifts in the Earth’s orbit around the sun.

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 800 000 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!

ice core ruler

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!

6. What discoveries have our scientists made?

ice

New Zealand’s ice coring programme, based at Victoria University Wellington and GNS Science has been underway since 1999. The aim of this research has been to understand what drives some of the major short term climate cycles in the Southern Hemisphere (such as the El Niño Southern Oscillation and the Antarctic Oscillation) and also how rapid shifts in the climate might be related to other environmental changes such as sea ice cover or the break up of ice shelves. 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 2004 and three other glaciers in Mount Cook National park in 2009.

7. 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

ice 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. This snow is put into sterile plastic bottles and then analysed in a laboratory to gain an initial idea of how well the chemical traces (or ‘signatures’) of the atmosphere are being retained in the snow.
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. 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.

ice core drill

8. 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 core gradually fills up the barrel and is then pulled up to the surface in roughly one meter lengths. It is then bagged in polyethylene, labelled and stored in insulated boxes for transport to a freezer and eventually to a processing lab such as ICICL.

9. What do you do next with the ice cores?

The analysis of ice cores is always done in a super clean laboratory so that there is no contamination of the ice. This is because some of the investigations involve measurements of minute quantities of trace elements.

Stratigraphy
First of all the ice core sections are placed on a transparent tray with a light underneath it. This shows up the different layers within the core, such as snow (firn) glacier ice and refrozen melt water. (pic of core and light tray) The different layers are recorded and graphed. The core sections are also weighed and measured so that their average densities can be calculated. Typically density increases as the surface snow is compacted at greater depth where it transforms into ice. ICL scientists have been pioneering the use of X-ray (DEXA) scanners to give very precise and high speed images of density variations in ice cores.

ice core cutting

Cutting
The next step is to slice the ice cores along their length with a bandsaw. Different parts of the core are used for different purposes and a large section is put aside for storage in the deep freeze as an ‘archive’. This can be used in the future for further research.

10. How do you analyse the ice?

Chemical analysis
The Ice Core Lab has a specially designed melter which melts the core without allowing any water to soak into the remaining ice. The water flows into small bottles and is then analysed for a wide range of chemical elements.

11. What sort of information can be found out by the analyses?

Dating
The analysis of an ice core is only useful if the ages of the ice layers are known. There are various methods that can be used depending on the approximate age of the ice, such as

  • Counting the annual layers based on visual appearance (summer layers are often darker due to more dust content or ice that has melted and then refrozen)
  • Measuring the concentration of particular radio isotopes with a known half life such as tritium, etc
  • Chemically matching volcanic layers with known eruptions that have been previously dated.

Ice core chemistry and climate
To give some simple examples of how the chemistry of the ice core will hold climate information think of the following:

  • Strong winds coming of the sea onto the glacier or ice cap would give rise to higher levels of sodium or chloride (salt). Depending where the sea is in relation to the drill site, this will give an indication of wind direction and strength.
  • A volcanic eruption will produce an increase in sulphur and acidity in the atmosphere which will get included in the ice core. Big eruptions can have a short term cooling effect on world climate due to the blocking of sunlight by the ash in the atmosphere
  • Colder climate conditions, leading to less vegetation and stronger winds will create an increase in dust layers in the core
  • The relative amounts of the heavier isotopes of hydrogen and oxygen in the ice are related to the temperature at the time the snow fell. For example when the temperatures are warmer, the snow will contain more of the heavier isotopes. This allows scientists to create a graph of temperature against time going right back to the oldest ice in the core.

Air bubbles trapped in the ice at the time of its formation allow scientists to analyse the gases that made up the atmosphere in the past. This information can then be related to climate changes, to identify how the atmospheric gases effect global temperatures.