Radiocarbon Dating of Soil Organic Matter

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Abstract
Radiocarbon ages of soil organic matter are evaluated with a model which incorporates the dynamics of the C-14 content of soil organic matter. Measured C-14 ages of soil organic matter or its fractions are always younger than the true ages of soils due to continuous input of organic matter into soils. Differences in soil C dynamics clue to climate or soil depth will result in significantly different C-14 signatures of soil organic matter for soils of the same age. As a result, the deviation of the measured C-14 age from the true age of soil formation could differ significantly among different soils or soil horizons. Our model calculations also suggest that C-14 ages of soil organic matter will eventually reach a steady state provided that no climatic or ecological perturbations occur. Once a soil or a soil horizon has beached a steady state, C-14 dating of soil organic matter will provide no useful information regarding the age of the soil. However, for soils in which steady state has not been beached, it is possible to estimate the age of soil formation by modeling the measured C-14 contents of soil organic matter. Radiocarbon dating of buried soils could, in general, overestimate the true age of the burial by as much as the steady-state age of the soil or soil horizon. (C) 1996 University of Washington