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Bumpy ice tells scientists about past climates.

After a 16-year detective hunt, glaciologists from the British Antarctic Survey have found bumps in the Antarctic ice sheet that will significantly improve the way that past climate conditions are reconstructed from ice cores.

The scientists are using ground-penetrating radar, the technique that the police use to find buried bodies, to locate these distortions, which they are calling Raymond Bumps, and which enable them to interpret the age of the ice.

"Glaciologists have searched for Raymond Bumps since 1983, when Charlie Raymond theorised that we should find distortions in the internal layers beneath the crests of some ice caps," explains BAS's Dr David Vaughan.

They are not visible from the surface, he adds, "and it is only now that we have the technology to find them".

Because of the extreme cold, winter snowfall in Antarctica rarely melts. This means that year-on-year the snow builds up to form layers, in a similar way to the annual growth rings of trees. These layers hold vital clues to the Earth's past climate.

The layers comprising Raymond Bumps are around 1.5 kilometres wide. The ground-penetrating radar device, which is towed over the ice cap on a sledge, builds a picture of layers up to 100 metres deep, and 300 years old. The layers themselves are expressions of density changes which provide scientists with a method of knowing which ones fell at the same time, says Vaughan. "No precipitation and high winds, for example, could produce a high-density layer, while a layer of hoar frost, with big crystals, could be fixed at the surface as a low density layer."

Ice cores are a good way of providing climatic information such as differences in summer and winter accumulation and greenhouse gas concentrations, as well as providing a record of nuclear explosions and volcanic eruptions.

But Vaughan says its vital to analyse Raymond Bumps as well. "If you ignore these bumps, the climate histories that you derive from ice cores could be seriously misleading," he warns.

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Author:McWilliam, Fiona
Date:Jun 1, 1999
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