EVALUATION OF PB-210 DATING IN LAKE-SEDIMENTS USING STABLE PB, AMBROSIA POLLEN, AND CS-137

We used sediment chronology data from fourteen published studies of la ke cores across much of North America and Scandinavia in order to make a large scale comparison of the different dating techniques. The unce rtainty of Pb-210 derived dates was determined using common sediment e vent markers: the stable Pb rise, the Cs-137 rise, and the Ambrosia po llen rise. For all data combined, the 95% confidence intervals for the stable Pb rise and the Ambrosia rise, were approximately 30 years. Th ese 95% confidence intervals are slightly higher than those derived by First-Order Error analysis performed by others on Pb-210 derived date s. When comparing the concordance of two Pb-210 models (CRS and CIC) a gainst markers of known history, we found that the CRS model dates (co nstant rate of supply) had consistently better agreement than the CIC model dates (constant initial concentration). Major discrepancies betw een Cs-137 and Pb-210 were common, but were consistently more severe i n sediments of soft water lakes pointing to an inability of sediments with low mineral content to 'immobilize' Cs.