A group of scientists, led by Prof. Jan Mangerud at the Bjerknes Centre for Climate Research and the Department of Earth Science, University of Bergen, has shown that glaciers in the nearest mountains east of Scandinavia behaved completely different from the Norwegian glaciers during the last glaciation. While glaciers in the Ural Mountains expanded only one km 20,000 years ago did the Scandinavian Ice Sheet reach Northern Germany, more than 800 km south of present day glaciers in the Norwegian mountains.
Glaciers in the Urals today and during the Ice Age
There is presently about 140 glaciers in the Urals. Scientists have earlier assumed they grew more or less parallel with other glaciers on the Northern Hemisphere during the glaciations, and therefore that they reached their maximum size some 20,000 years ago. Mangerud and co-workers have mapped and dated moraines in the Polar Urals. And indeed, there are moraines showing that large glaciers have existed in the Urals, but it turned out that they are 60,000 years old. The 20,000-years-old moraines were found only one km outside the present day glacier.
How to determine the age of the moraines?
A crucial point in all historical sciences, climate history as cultural history, is to determine the age of the event in question. In this study is used a method where the duration of exposure of a rock surface to cosmic rays are measured. The glaciers eroded large boulders from the bedrock and deposited them on the moraines. The fresh surface of these boulders offers a starting point for the used geologic clock. Cosmic rays produce Beryllium in quartz and this can be compared with an hourglass, the longer the surface has been exposed the more Beryllium is accumulated in the quartz. Boulders on the moraine one km outside the glacier yielded ages of about 20,000 years, whereas boulders down-valley of the moraine yielded more than 50,000 years.
Large regional differences in climate change
The large difference in growth between Scandinavian and Uralian glaciers reflects large regional differences in climate change. This can be compared with modelling predictions of future changes; most places will be warmer, but some will be wetter and others drier. However, the fluctuations and differences were larger during the ice ages. Two climatic factors trigger glacier growth: Either more snow fall during the winter or less melting during the summer, or a combination of these factors. The summers were much colder in the Urals 20,000 years ago, so the only explanation for the limited growth of the glaciers is that the climate was extremely dry. A part of the explanation is that the Scandinavian Ice Sheet caught the precipitation under way to the Urals, but why then could the Uralian glaciers grow earlier?
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| The studied Chernov Glacier in the Urals. The Little Ice Age moraine is only a couple of centuries old. The man is standing on a boulder dated to be 21,600 years old with an uncertainty of 1600 years. The latter is located on the moraine from the Last Glacial Maximum. |
Reference:
Mangerud, J., et al., Glaciers in the Polar Urals, Russia, were not much larger during the Last Global Glacial Maximum than today. Quaternary Science Reviews (2008).