Dating recent peat deposits

Dating recent peat deposits (i.e., past } 300 yrs of peat accumulation) has emerged as an important yet challenging task for estimating rates of organic matter accumulation and atmospheric pollutant deposition in peatlands. Due to their ombrotrophic nature and the tendency for Sphagnum-derived peat to have high cation exchange capacity, peatlands are ideal archives of atmospheric pollution. However, efforts to establish depth-age relationships in peats are complicated by the difficulty of dating deposits reliably. Assumptions underlying the techniques available for dating peat deposits often are poorly understood and generally untested. We outline the approaches used to establish depth-age relationships in peat chronologies, including brief descriptions of the theory, assumptions, methodology, and logistics of each technique. We include both continuous dating methods (i.e., methods based on 14C, 210Pb, constant bulk density, acidinsoluble ash, moss increment, pollen density) and chrono-stratigraphic markers (i.e., fallout isotopes from the Chernobyl accident and nuclear weapons testing, pollen stratigraphies, isothermal remanence magnetism, charcoal particles, spherical carbonaceous particles, PAHs, PCBs, DDT, toxaphene) that can be measured in peat and correlated temporally with known historical events. We also describe the relatively new radiocarbon application of wiggle matching and use hypothetical data to highlight the potential of this developing technique for dating recent peat. Until the uncertainty associated with each of these dating approaches is clarified, we recommend employing multiple techniques to allow for corroboration between different methods.