AMS ¹⁴C measurements of fractionated soil organic-matter - an approach to deciphering the soil carbon-cycle

C-14 measurements are reported for fractionated soil organic matter from a genetic soil sequence which was sampled several times during the period of atmospheric nuclear weapons testing. Fractionation of the soils by density followed by acid hydrolysis was successful in separating the organic matter into components with mean residence times for carbon ranging from 5 to 20 years (low density fraction) to several thousand years (residue after acid hydrolysis). Comparison of the infiltration of bomb C-14 into the vertical soil profile with the distribution of Cs-137, gives clues as to the mechanism (most probably dissolved transport) for importing carbon into deeper soil layers