Flow cytometric techniques in Quaternary research: Improving radiocarbon age determination and evaluating potentials of stable isotope and aDNA analyses based on high-purity fossil pollen samples

• Applicant: Dr. Christian Leipe
• Subject Area: Palaeontology ; Physical Geography
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 400195333

The analysis of fossil pollen assemblages (i.e. pollen analysis = PA) is one of the most frequently used methods in Quaternary research and has significantly contributed to our understanding of past environmental changes, human–environment interactions, land use history and the origin and spread of agriculture. The existing pollen-based reconstructions, including qualitative and quantitative approaches, take into account the absence/presence of indicator-taxa and/or the taxa percentages in the examined sediment samples. Recent studies have indicated potential of pollen-derived stable isotope and ancient DNA (aDNA) records for Quaternary research. Stable isotope signals of terrestrial pollen have been suggested as a new palaeoclimate proxy that would overcome the time lag between climate change and vegetation response. The latter is a serious constraint in PA, particularly in high-resolution studies. Pollen aDNA has shown to be capable for identifying source plants to species level, which is seldom possible by traditional PA and would allow precise identification of ecological/climatic indicator taxa, ancient domesticates, and spread of crops. The application of fossil pollen in radiocarbon dating helps to overcome errors in age determination due to reservoir effects, which most sedimentary archives suffer from. All mentioned research methods require effective extraction of pure pollen concentrates comprising entire spectra or selected taxa. My own preliminary investigations and the experiments of colleagues have shown that flow cytometry is a promising approach to accomplish this task. In this project, I will first focus on extracting clean, contamination-free pollen fractions from the well-dated and reservoir-free upper part (0–6000 years before present) of the Lake Kushu (northern Japan) RK12 sediment core based on flow cytometry using different technical approaches and devices. In a second step, I will measure stable isotope compositions (δ13C and δ18O) of selected pollen taxa (e.g. fir and oak) fractions extracted from the RK12 core. DNA analysis will be tested for detection of selected ecological indicator species and domesticated crops including barley and millets. I will also perform radiocarbon dating on pollen concentrates. The results will be compared with those obtained using conventional techniques on the RK12 core. If these tests are completed successfully, in a third step, the methods will be applied to different sediment sections from East and Southeast Asia comprising the lower, less well dated part of RK12 and one each from central Japan and northern Vietnam. These applications aim at optimizing workflows and gaining deeper insights into the evolution of the East Asian summer monsoon and short-term climate variations during the late-glacial–Holocene interval. Moreover, I intend to detect the cultivation/spread of different domesticated plants (barley, millets, rice).

• DFG Programme: Research Fellowships
• International Connection: Japan
• Host: Professor Dr. Hiroyuki Kitagawa