Analytical and sampling constraints of 210pb dating
The bias in calculated ages increases with poorer limit of detection and the magnitude of the disparity increases with age. is an environmental laboratory and consulting firm in Winnipeg, Manitoba, Canada. Robert Flett (Ph D), the company specializes in the analysis of mercury and environmental radioisotopes.The dating of sediment cores by the Pb-210 method can be used to determine the sediment accumulation rate for a body of water and the age of the sediments at a particular depth can be inferred.The age of sediments at different depths can be used to document historical contamination.The Constant Rate of Supply (CRS) model is the most versatile and widely used method for establishing Pb chronologies but, when using this model, care must be taken to account for limitations imposed by sampling and analytical factors.In particular, incompatibility of finite values for empirical data, which are constrained by detection limit and core length, with terms in the age calculation, which represent integrations to infinity, can generate erroneously old ages for deeper sections of cores.The study indicated that neither 137Cs nor 32Si could be used to derive reliable chronologies for peat.Implied temporal variations in deposition of anthropogenic species (ash, Pb and Pb isotopes) were consistent with known historical variations and other studies of archived materials, lake sediments and peat deposits.
The discussion is illustrated with examples from tidal flat, salt marsh and fjord sediments from temperate settings but the problems are universal and should be equally relevant for estuarine settings in other climatic zones.The study demonstrated that with a limit of detection of 5 Bq kg-1 or better, rigorous sampling technique and high resolution (2 cm) sampling increments, 210Pb dating using either the CIC method or the CRS method and 241Am dating method all gave consistent chronologies.