Dynamics of pedogenic carbonate for the last 5000 years and its role as a buffer reservoir for atmospheric carbon dioxide in soils of Russia

The carbon isotopic composition of humus and carbonates was determined in the soils of the Selenga Range and in paleosols buried beneath mounds of various ages on the Russian plain. All of the soils contained both carbonate remnants inherited from the source rocks and pedogenic carbonates formed during soil formation. The proportions of pedogenic and lithogenic components can be calculated from the carbon isotopic composition of humus and soil carbonates. The abundance of pedogenic carbonates depends primarily on the climate condition, i.e. soil type and, to a lesser extent, soil age and content of lithogenic clasts in the parent material. Two epochs of carbonate formation are clearly manifest in the soils of European Russia. These epochs coincide with the periods of arid climates about 3750 and 2300 years ago. In the course of soil formation for the last 5000 years the soils fixed atmospheric carbon dioxide as pedogenic carbonate during the arid periods at a rate of 2.2 kgC/m2 a year in chernozem (Typic Calciustoll), 1.13 kgC/m2 a year in dark-chestnut soil (Typic Haplocalcid), 0.86 kgC/m2 a year in light-chestnut soil (Typic Natrargid). So, together, during the most recent 3500–5000 years, the soils sequestered CO2 from the atmosphere within carbonates and so served as an additional sink in the carbon cycle. Soil carbonates are a sink for СО2, representing approximately 2.6% of the common emission of СО2 from soils.