Carbon in tundra soils in the Lake Labaz region of arctic Siberia

Large amounts of carbon are stored in permafrost-affected soils of the Arctic tundra. The quantity, distribution and composition of this carbon are important, because much of the carbon is likely to be released as a result of global warming. We have studied soils of the central Siberian Arctic to determine the carbon content and the nature of the organic matter by density fractionation, and (13)C-NMR- and (13)C-stable-isotope analyses. There are pronounced differences in the profile and variations from place to place in the quantity and nature of soil organic matter. We estimated that the mean stock of carbon was 14.5 kg m(-2) within the active layer. We found a total of about 30.7 kg C m(-3) in the entire upper metre of the soils. Carbon of the tussock tundra showed strong vertical differentiation, with a large proportion comprising decomposed, recalcitrant compounds. We identified within the soil several zones of aerobe and anaerobe decomposition. Mobile carbon fractions have precipitated under the influence of low temperatures.