An ice core is a long cylinder of glacial ice recovered by drilling through glaciers in Antarctica and Greenland.
Scientists use core samples to look for clues about the climate at the time the snow fell, as they are able to retrieve details of atmospheric composition, temperature and abrupt changes as far back as 100,000 years or more from the accumulated ice within the core.
Antarctica
Throughout each year, layers of snow fall over the ice sheets of Antarctica and Greenland. As each layer of snow falls, it carries with it minute bubbles of air and traces of any impurities in the atmosphere at the time, such as wind-blown dust, ash, bubbles of atmospheric gas and radioactive substances. Each layer of snow is therefore different in chemistry and texture, with summer snow differing from winter snow.
As the snow layers accumulate, the buried snow is compressed and forms firn, a grainy material with a texture similar to granulated sugar. As snow builds up above, the firn continues to become compressed into ice; trapping the impurities and samples of air too.
By drilling an ice core from the right site, scientists can reconstruct an uninterrupted and detailed climate record extending over hundreds of thousands of years, providing information on a wide variety of aspects of climate at each point in time. You might say Antarctica has been cold for thousands of years - and you would be right. However, scientists have found there is great variation in the degree of cold that the region has experienced over the centuries.
After drilling out a long core of glacial ice, small samples from along the core can be analysed to see how things have changed over time. In this way, the snow layers become a permanent record of atmospheric conditions going back far into the past and each layer gives scientists a wealth of information about the climate each year as an ice core provides a vertical timeline of past climates stored in ice sheets.
BAS Scientists at work in Antarctica - BAS
Furthermore, scientists are using data obtained from ice cores to help predict how greenhouse gases might affect global climate in the future. Recent findings from ice cores show that current carbon dioxide (CO2) levels are higher than they have been in 440,000 years. Nobody quite knows how this will alter our climate, but researchers hope a detailed picture of past changes will give them a better idea of what we can expect in the future.
The length of climate record obtained by scientists from an ice core depends on the depth of the ice core and this varies from a few years up to many thousands of years. Until 2003, the longest core drilled in Antarctica reached back 420,000 years and revealed four past glacial cycles. But recently, a three-kilometre-long ice core drilled from the Antarctic, has confirmed global climate patterns stretching back 740,000 years.
The European Project for Ice Coring in Antarctica (EPICA) has recently extracted a 3200 metre ice core from a location called Dome C, formally known as Dome Charlie, a massive ice dome in the enormous snow plateau of Wilkes Land. Tests confirm that the ice core dates back at least 750,000, making the ice the oldest continuous core ever retrieved.
Dome C is one of the coldest places on Earth. Located at 74°. 39’ S; 124°.10’E at an elevation of 3,240 metres, temperatures hardly rise above -25°C in summer and can fall below -80°C in winter. The mean annual air temperature at the site is -54.5° C.
EPICA Dome C Ice Core
This mammoth core has now been cut into sections and shipped to labs in the 10 European countries in the EPICA collaboration for further examination.
One way of dating ice in a core is to count the layers laid down annually, but in the Dome C core, they are too thin to distinguish. So, researchers have used markers such as dust, gas and electrical conductivity in the ice to match different layers to known events that have already been dated, such as volcanic eruptions or ice ages.
The results have confirmed that the first 3140 metres of the core date back 750,000 years. The next step is to check that all the layers of the core are still in chronological order. If they are, scientists are suggesting that the deepest ice could be up to a million years old and may prove invaluable to discerning future trends for our climate.
But already examination of this mammoth ice core by EPICA scientists has revealed that over the last 800,000 years the Earth has, overall, been a chilly place. Interglacials - or warm spells - have come every 100,000 years and have generally been short-lived.
Over the last 400,000 years, interglacials have lasted about 10,000 years, with climates similar to our present one. Before that, they were less warm, but lasted slightly longer.
We have already been in an interglacial for about 10,000 years, so we should - according to the pattern - be heading for an ice age. But we are not. The EPICA team has noticed the interglacial period of 400,000 years ago closely matches our own - because the shape of the Earth's orbit was the same then as it is now. That warm spell lasted an amazing 28,000 years - so the EPICA scientists feel ours probably will, too.
The EPICA scientists hope to publish further findings in a few months.