Shifts in 14C Patterns of Soil Profiles Due to Bomb Carbon, Including Effects of Morphogenetic and Turbation Processes

Abstract

Principles contributing to changes and the final balance of rejuvenation in 14C dates of soil profiles are identified. The annual addition to the atmosphere of ca 5.5 . 10^12 g dead carbon from fossil carbon sources and 1.5 . 10^12kg of older carbon from forest clearing make soil appear older. Bomb carbon and annual recycling of most of the 115 . 10^12kg of terrestrial organic carbon, equivalent to the annual photosynthetic turnover of carbon, rejuvenates soil dates. This also applies to root growth, animal transport, and in acid or alkaline soils, to humus percolation. All available 14C dates of soil profiles were evaluated for the impact of bomb carbon. We also studied the effects of morphogenetic soil-forming processes, such as turbations, on soil rejuvenation. Bioturbation, as a general principle of soil dynamics, requires more differential treatment due to modern and bomb carbon that constitutes body carbon of earthworms as well as steadily increasing 14C age with depth in all Mollisols.