Russia's soil: Is it a CO2 source or sink?

The carbon isotopic composition of humus and carbonates was determined in t he soils of the Selenga Range and in paleosols buried beneath mounds of var ious ages on the Russian plain. All of the soils contained both carbonate r emnants inherited from the source rocks and pedogenic carbonates formed dur ing soil formation. The proportions of pedogenic and lithogenic components can be calculated from the carbon isotope composition of humus and soil car bonates. The abundance of pedogenic carbonates depends primarily on the soi l type and, to a lesser extent, soil age and content of lithogenic clasts i n the source rock. Two epochs of carbonate formation are clearly manifested in the soils of european Russia. They coincided with the periods of arid c limates about 4000-3500 and 2300 years ago. During soil formation, the soil s of Transbaikalia bound from 26.44 to 14.5 kg/m(2) atmospheric carbon diox ide for chernozem and 11.8 kg/m(2) for chestnut soils. However, the removal of CO2 as total carbonates is much higher than the CO2 fixation in pedogen ic carbonates. Thus, during the most recent 3500-5000 years, the soil relea sed CO2 from carbonates and served as an additional source of it in the car bon cycle through groundwater and surface water.