Antarctic: thaw five million years ago

Researchers tap climate archive under the ice

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Five million years ago in the Antarctic it was so hot that large parts of the glaciers melted away. Scientists have now found this out in the analysis of cores that they have obtained as part of the Antarctic Geological Drilling Program (ANDRILL). The warm period lasted about a million years and affected other parts of the world.

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The earth heats up. Slow but steady. By the year 2100, global temperatures will rise by an average of two to five degrees Celsius. Climate change - hardly anyone doubts today - is there. But what consequences does global warming have for life on our planet? "Reliable statements can only be made on the basis of reliable comparative data, " says Professor Lothar Viereck-Götte of the University of Jena. To estimate how the sea level will rise through melting glaciers, one must know how high it was in earlier times, when the climate on Earth was still much warmer than it is today.

This is exactly what the professor of geochemistry hopes to find through a targeted look into the climate history of our planet: under the ice of the Antarctic. "In the sediment layers under the mighty ice sheet, information about the climatic conditions of the past is stored in an archive, " says Viereck-Götte. With the first drilling of the "ANDRILL" drilling program, a 200-strong international research team of geoscientists, climate researchers and technicians, including Viereck-Götte and his Jena employee Andreas Veit, has now tapped this "climate archive".

"ANDRILL" (Geological Drilling in the Antarctic) is a joint program of the US, Italy, New Zealand and Germany to study Earth's climate evolution through drilling on the Antarctic continent. The first hole passed through the more than 80 meters thick ice of the Ross shelf - the glacier ice, which slides off the land and floats on the sea water - into the 800 meters deeper seabed. With every meter that the drill buried in the sediments, he came back about 10, 000 years to the geological past. display

Looking back on twelve million years

A total of 1, 284 meters and 87 inches deep, the high-tech drill has worked in the layers. "This means we can use the cores that have been preserved to look back about 12 million years in the history of icing at the South Pole, " says Viereck-Götte, head of the German "ANDRILL" commission.

The Jena geoscientist is thrilled with the quality of the cores. "So far, there has been no drilling in the Antarctic or Ocean Area where solidified rocks with a core gain of 98 percent have been recovered." Although the work of the scientists is only just beginning, initial investigations of the cores on site have already amazed the researchers.

As can be seen, for example, from the large amounts of layers of diatoms, it must have been so warm in the Antarctic about five million years ago that the glaciers of the West Antarctic and parts of the eastern Antarctic melted away. "This warm period lasted almost a million years and was not confined to the Antarctic, " says Viereck-Götte. Indications of a global warm period are also to be found at the bottom of the Mediterranean Sea and in Cappadocia in central Turkey.

"In the three and a half million years that followed this time, the global climate changed constantly", interprets Viereck-Götte the data obtained from the ANDRILL project. Only within the last one million years are the glaciers in the Antarctic more stable. "Fluctuations in the climate, " according to the Jena researcher, "are therefore more the norm and not the exception.

More detailed analyzes follow

After the preliminary investigations on site, more detailed analyzes of selected samples in the laboratory are now to follow. The cores, which are currently still in the Antarctic, are brought by ship to Florida in the spring. In Tallahassee, the entire international ANDRILL team will meet in May. Viereck-Goette will also be there to select the samples that the Jena geoscientists will then conduct research on over the next two years.

He and his colleagues in G ttingen want to take a closer look at the chemical composition of the sediments and individual particles excavated while Veit is interested in the chemical and mineralogical composition of the volcanic ash layers in the cores.

(idw - University of Jena, 01.03.2007 - DLO)