RADIOCARBON DATING OF SOIL ORGANIC-MATTER

Radiocarbon ages of soil organic matter are evaluated with a model whi ch incorporates the dynamics of the C-14 content of soil organic matte r. Measured C-14 ages of soil organic matter or its fractions are alwa ys younger than the true ages of soils due to continuous input of orga nic matter into soils. Differences in soil C dynamics clue to climate or soil depth will result in significantly different C-14 signatures o f soil organic matter for soils of the same age. As a result, the devi ation of the measured C-14 age from the true age of soil formation cou ld differ significantly among different soils or soil horizons. Our mo del calculations also suggest that C-14 ages of soil organic matter wi ll eventually reach a steady state provided that no climatic or ecolog ical perturbations occur. Once a soil or a soil horizon has beached a steady state, C-14 dating of soil organic matter will provide no usefu l information regarding the age of the soil. However, for soils in whi ch steady state has not been beached, it is possible to estimate the a ge of soil formation by modeling the measured C-14 contents of soil or ganic matter. Radiocarbon dating of buried soils could, in general, ov erestimate the true age of the burial by as much as the steady-state a ge of the soil or soil horizon. (C) 1996 University of Washington.