Ice Age ended with gigantic burp

About 13,000 and 18,000 years ago, carbon dioxide poured into the atmosphere in two giant belches that drove concentrations of the greenhouse gas from 180 to 265 parts per million, a level that held relatively steady until the industrial revolution. In a report published in the journal Science, researchers said they had found the answer in a sample of sediment drilled in the Pacific ocean.

• The researchers first correlated the bands of sediment in the core drilled off Baja California, Mexico, with the Greenland ice cores. Embedded in the 15-metre-long Baja core were shells left by micro-organisms;

•  The researchers analysed the shells to determine the ratio of two isotopes, carbon-12 and carbon-14. Carbon-14 is produced by cosmic rays in the atmosphere. Thus, so-called "old water" that stays deep in the oceans for thousands of years contains relatively little carbon-14 and lots of carbon-12;

•  The researchers found two periods stood out for their low carbon-14 levels. This meant water was barely circulating to the surface: carbon from decaying organic material was accumulating in the deep. However, the old water eventually rose to the surface, releasing its carbon dioxide in an enormous burp – and each of these gas releases was recorded in the Greenland ice cores. The burps injected 640 gigatonnes of carbon dioxide into the atmosphere when the Earth was already emerging from an ice age. What started the warming is unknown, but scientists said the release of the gas accelerated it. Over a 10,000-year span, global temperatures rose by more than 14 degrees.

The Sydney Morning Herald, 12/5/2007, p. 15

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