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Journal Article

Factors and processes governing the 14C content of carbonate in desert soils

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Amundson, R., Wang, Y., Chadwick, O., Trumbore, S. E., McFadden, L., McDonald, E., et al. (1994). Factors and processes governing the 14C content of carbonate in desert soils. Earth and Planetary Science Letters, 125(1-4), 385-405. doi:10.1016/0012-821X(94)90228-3.

Cite as: http://hdl.handle.net/11858/00-001M-0000-0028-12CD-F
A model is presented describing the factors and processes which determine the measured C-14 ages of soil calcium carbonate. Pedogenic carbonate forms in isotopic equilium with soil CO2. Carbon dioxide in soils is a mixture of CO2 derived from two biological sources: respiration by living plant roots and respiration of microorganisms decomposing soil humus. The relative proportion of these two CO2 Sources can greatly affect the initial C-14 content of pedogenic carbonate: the greater the contribution of humus-derived CO2, the greater the initial C-14 age of the carbonate mineral. For any given mixture Of CO2 Sources, the steady-state (CO2)-C-14 distribution vs. soil depth can be described by a production/diffusion model. As a soil ages, the C-14 age of soil humus increases, as does the steady-state C-14 age of soil CO2 and the initial C-14 age of any pedogenic carbonate which forms. The mean C-14 age of a complete pedogenic carbonate coating or nodule will underestimate the true age of the soil carbonate. This discrepancy increases the older a soil becomes. Partial removal of outer (and younger) carbonate coatings greatly improves the relationship between measured C-14 age and true age. Although the production/diffusion model qualitatively explains the C-14 age of pedogenic carbonate vs. soil depth in many soils, other factors, such as climate change, may contribute to the observed trends, particularily in soils older than the Holocene.