Pollen 14C dating compared with established dating methods: Capabilities and limitations of sorting with flow cytometry

Radiocarbon (14C) dating is a powerful tool for establishing reliable chronologies for proxy records recovered from environmental archives, including lacustrine sediments. However, lacustrine sediments are often limited with respect to availability of material such as terrestrial macrofossils that are traditionally targeted for 14C dating. Flow cytometry, in combination with physicochemical preprocessing, is an emerging technique for the isolation of pollen from terrestrial sediments, holding the promise of pollen recovery of sufficient purity and efficiency for routine 14C analysis. Here, we examine the performance of this approach by undertaking a comprehensive blank assessment for a new pollen isolation protocol and comparing pollen-14C data against established chronologies for two lake records. Our procedure yields consistent values for constant contamination with extraneous carbon of 1.34±0.40 μg C and an F14C of 0.85±0.04, rendering our method suitable for microscale 14C analysis. The pollen-14C data are largely in agreement with age estimates for the same layers of the lake sediment cores based on macrofossil-14C analysis and tephrochronology. However, we also observe that our pollen samples appear to be, on average, slightly older than their macrofossil counterparts. We hypothesize this to be the result of sedimentary and translocation processes that retard pollen transport and lacustrine deposition.