Going with the flow: rapid pollen sorting for radiocarbon analysis
Nakajima K1,2, Heusser C1,2, Welte C1,2, Wacker L2, Eglinton T1
1Geological Institute, ETH Zürich, Zürich, Switzerland, 2Laboratory of Ion Beam Physics, ETH Zürich, Zürich, Switzerland
Pollen grains have long been suggested ideal targets for radiocarbon (14C) dating of terrestrial sediment records. They are ubiquitously abundant in lacustrine sediments and represent atmospheric 14C concentrations as they form each year. Because pollen are established markers for terrestrial ecosystem variability, pollen-based 14C data provide the ideal, proxy-specific chronology for palynological research. Traditional approaches for pollen separation from sedimentary matrices have proven difficult due to a trade-off between purity, processing time, and yield. In recent years, a growing number of studies have demonstrated the suitability of flow cytometry cell sorters, in combination with physical and chemical processing, for the rapid separation of pollen grains from terrestrial sediments at high purity, e.g., [1]. With a dedicated flow cytometer (BD Influx Cell Sorter, BD Biosciences, US), we examine the robustness of this novel approach to isolate pollen grains for 14C analysis. We will provide the relevant parameters for reliable sorting and a detailed assessment of sorting efficiencies. First 14C results with elemental-analyzer-accelerator-mass-spectrometry of blank assessments at different preparation stages of the pollen separation and finally of natural sediment samples show that our protocol is suitable for microscale (< 20 µg C) pollen-14C dating. This will enable the dating of sediments previously limited by the lack of suitable material. With an established protocol and a dedicated instrument paving the way for routine application, pollen-14C dating will provide a versatile alternative to traditional dating approaches for terrestrial records.
[1] R. K. Tennant et al. (2013), JQS 28(3), 229-236.