Conservation of soil organic matter through cryoturbation in arctic soils in Siberia

Abstract

Cryoturbation (mixing of soil layers due to repeated freeze-thaw processes) is a major soil forming process in arctic regions, which may contribute to long-term storage of C in soils of northern latitudes. Our goal was to determine the effect of subduction of organic matter by cryoturbation on microbial decomposition processes in tundra soils. Buried layers were situated at 30-60 cm depth, between Bg and B horizons, but exhibited a C and N content highly similar to present-day A horizons. Radiocarbon dating revealed, however, that the mean age of C in the buried layer was three times higher (≁ 1300 years BP) than in the A horizon (∼400 years BP), suggesting that decomposition rates in the buried layer were delayed. The observed microbial processes support this result: gross C and N mineralization rates were substantially lower in the buried layers than in the respective A horizons. The amount of C stored in the buried layer still doubles the amount of C stored in topsoil horizons (O and A). Assuming that the buried layer originates from both O and A horizons, this indicates that O and A horizon at time of burying (800-1300 years BP) must have been significantly thicker and present-day O and A horizon at this site may still have the capacity to accumulate additional C. Cryoturbation therefore may lead to additional long-term storage of carbon in the system by (1) retarding decomposition processes of buried organic material and (2) enabling the soil to restart C accumulation in topsoil layers. Copyright 2007 by the American Geophysical Union.