A team from the Earth and Space Sciences Department at the University of Washington (Seattle) is proposing to revalue the organic carbon content of soils at very high latitudes up sharply.
While stocks have so far been estimated at 1 billion tonnes in the peripheral Arctic desert and 17 million tonnes in the Arctic desert itself, Ronald Sletten and his colleagues suggest 8,7 and 2,1 billion tonnes respectively for these two areas.
They are based on the results of field work carried out over three successive summers over an area of 365 km2 in north-west Greenland.
Unlike previous studies, the permafrost samples analyzed were not limited to the surface part of the soil (the first 25 centimeters), but were taken to a depth of one meter.
The researchers then was surprised to see the presence of high concentrations of organic carbon in the lower horizons of the soil.
According to them, this burial of carbon would be due to a phenomenon of "cryogenic mixing".
Admittedly, the studied sector represents only a little more than 0,01% of the surface of the polar zones concerned on a global scale. But if the validity of the extrapolation made by Dr. Sletten's team were confirmed, the melting of permafrost would produce, by massive release of greenhouse gases, a much more dramatic positive feedback than expected on global warming.
This work was presented at the fall session of the American Geophysical Union (San Francisco, December 5-9).