Dating antarctic ice cores
A variety of different analyses techniques are used to extract that information.
As more and more snow is accumulated on top, the underlying snow is compressed into ice and the air forms bubbles in the ice.Measuring the delta value at many depths through the ice core is equivalent to measuring the air temperature at many times in the past. Climatic temperature against time from delta measurements taken on the ice core drilled at the Russian station, Vostok, in central Antarctica (Figure 2).Available data from this ice core so far extends back about 160,000 years.Approximately 98 per cent of the Antarctic continent is covered by the ice sheet which is on average about 2,500 metres thick and, at it's deepest location, 4,700 metres thick.It is due to this thick ice mass that Antarctica is, on average, the highest continent.Ice cores therefore can be analysed not just for the chemical and physical properties of the ice, but also for the properties of the air trapped in the ice.These bubbles are actual samples of the atmosphere up to thousands of years ago.These short warmer periods are called inter-glacials. From 120,000 to about 20,000 years ago, there was a long period of cooling temperatures, but with some ups and downs of a degree or two.This was the Wisconsin Period, known as the last Great Ice Age.However, drilling of the core still continues, and it is expected that, when drilling is completed in a few years time, an age of 500,000 years will have been reached.Starting on the right-hand side of the graph at about 140,000 years ago, the climate was about 6°C colder than it is today. Then at about 130,000 years ago, there was a quite rapid warming period until about 125,000 years ago, when the climate was, perhaps, 1°C or 2°C warmer than today.