Warning in the stalagmites

Ocean sequestring gets more difficult to understand

Published: Tuesday 31 July 2001

 Stalagmites from the Blue hol studying a half-metre-long stalagmite recovered from a now submerged cave in the Bahamas has shown that there were dramatic changes in the amount of radioactive carbon swirling around in the Earth's atmosphere during the last Ice Age. The changes were far greater than previously believed.

The findings serve a warning that climate change could affect the carbon cycle in ways not yet understood. The discovery was made by Warren Beck, assistant research scientist at Arizona University, usa . The information could have major implications for our understanding of past and future climate change.

The stalagmite was brought up from the Blue Holes of the Bahamas, the complex of limestone caverns created when sea levels were more than 100 metres lower than they are today. Because of the way they form, stalagmites can be used to determine past levels of radiocarbon in the atmosphere. They help establish a timescale for dating, and this information is checked against the more accurate method of uranium dating.

In this case, scientists from the Universities of Bristol, Arizona and Minnesota were able to look back 45,000 years ago -- well into the last Ice Age. Their analysis revealed huge peaks in radiocarbon levels -- much greater, than can be explained merely by an increase in cosmic ray bombardment on the Earth. The best explanation put forward is that there would have been a reduction in the amount of carbon dioxide dissolved into water -- something that could have happened if the oceans began to circulate more slowly in the cold climate of the Ice Age.

There is already some evidence for this slow-down. And there is data to indicate that this slow-down may soon occur again, although this time it is likely to be driven by the warming of the climate.

The observation that the carbon cycle was significantly more sluggish in the recent past throws up a plethora of questions regarding the oceans' capacity to take up human-produced co 2 emissions from fossil fuel burning "We should take this as a warning that climate changes may affect the carbon cycle in previously unexpected ways.

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