5:15 PM - 6:30 PM
[HQR04-P09] Radiocarbon dating using pollen fossils and its potential in Quaternary studies
Keywords:radiocarbon, pollen
Radiocarbon dating is one of the most widely used dating methods in Quaternary science, including paleoclimatology, archaeology, and hazard protection. Macrofossils (e.g., leaves, wood fragments, and shells) and bulk sediment samples have been used for dating in terrestrial studies. However, macrofossils are not always included in sediments. Moreover, depending on the sedimentary and post-depositional processes, these materials are often not suitable for dating. Therefore, the possibility of radiocarbon dating using small plant fragments and microfossils, which are generally expected to have better radiocarbon integrity, has been explored.
Fossil pollen grains are often found in terrestrial sediments and are one of such materials that have potential to yield more robust radiocarbon ages. Pollen membranes consists of sporopollenin, a physicochemically stable organic polymer. Sporopollenin contains ca. 60% of carbon and has been studied since the 1990s as a potential material for radiocarbon dating. While these studies have successfully shown that fossil pollen grains are potentially suitable for 14C dating, their applications in actual researches have been very limited.
One of the limiting factors is the difficulty of extracting fossil pollen grains from sediment matrixes in high purity. We need to concentrate fossil pollen grains because they comprise very small part of the sediments. However, the characteristics of pollen fossils, such as size, specific gravity, and chemical tolerance do not differ significantly from those of other organic materials in sediments. Therefore, it is difficult to isolate pollen grains using only conventional physicochemical treatments. In this study, we established a novel method to extract fossil pollen grains using “cell sorter” in combination with new physicochemical treatments. Cell sorters can separate individual particles based on scattered light and fluorescence.
In this study, we used SG06 core obtained from Lake Suigetsu, Fukui prefecture, Japan, Radiocarbon ages of >800 terrestrial leaf fossils have been measured, making the core almost ideal target for comparison to assess robustness of the radiocarbon dates obtained on fossil pollen pellets.
The extracted pellets are composed almost exclusively of pollen grains, with almost no solid impurities. The size of the extracted pollen grains depends on the specs of the cell sorter. Therefore, the extracted pollen fossils consist of grains with diameters of 10-50 μm, such as Cryptomeria and Alnus, and do not retain the original percentage composition of fossil pollen assemblage.
The radiocarbon ages obtained on fossil pollen pellets prepared by cell-sorter precisely reproduced those from leaf macro fossils, regardless of the taxa percentage composition. These agreements were maintained even near the radiocarbon limit (ca.50 ka). The fossil pollen grains extracted by our method were useful as materials for radiocarbon dating, as is also the case with the terrestrial leaf fossils. Our method enables robust radiocarbon dating of the sediments that do not contain macro remains suitable for radiocarbon dating.
We also confirmed that fossil pollen grains could be extracted from not only lacustrine deposits, but also peat and volcanic soils. The extraction method can be applied to a range of terrestrial sediments deposited in various environments. Combined with Bayesian modeling, radiocarbon dating of strategically chosen horizons can provide much stronger age constraints to event deposits such as volcanic ash and tsunami deposits.
Fossil pollen grains are often found in terrestrial sediments and are one of such materials that have potential to yield more robust radiocarbon ages. Pollen membranes consists of sporopollenin, a physicochemically stable organic polymer. Sporopollenin contains ca. 60% of carbon and has been studied since the 1990s as a potential material for radiocarbon dating. While these studies have successfully shown that fossil pollen grains are potentially suitable for 14C dating, their applications in actual researches have been very limited.
One of the limiting factors is the difficulty of extracting fossil pollen grains from sediment matrixes in high purity. We need to concentrate fossil pollen grains because they comprise very small part of the sediments. However, the characteristics of pollen fossils, such as size, specific gravity, and chemical tolerance do not differ significantly from those of other organic materials in sediments. Therefore, it is difficult to isolate pollen grains using only conventional physicochemical treatments. In this study, we established a novel method to extract fossil pollen grains using “cell sorter” in combination with new physicochemical treatments. Cell sorters can separate individual particles based on scattered light and fluorescence.
In this study, we used SG06 core obtained from Lake Suigetsu, Fukui prefecture, Japan, Radiocarbon ages of >800 terrestrial leaf fossils have been measured, making the core almost ideal target for comparison to assess robustness of the radiocarbon dates obtained on fossil pollen pellets.
The extracted pellets are composed almost exclusively of pollen grains, with almost no solid impurities. The size of the extracted pollen grains depends on the specs of the cell sorter. Therefore, the extracted pollen fossils consist of grains with diameters of 10-50 μm, such as Cryptomeria and Alnus, and do not retain the original percentage composition of fossil pollen assemblage.
The radiocarbon ages obtained on fossil pollen pellets prepared by cell-sorter precisely reproduced those from leaf macro fossils, regardless of the taxa percentage composition. These agreements were maintained even near the radiocarbon limit (ca.50 ka). The fossil pollen grains extracted by our method were useful as materials for radiocarbon dating, as is also the case with the terrestrial leaf fossils. Our method enables robust radiocarbon dating of the sediments that do not contain macro remains suitable for radiocarbon dating.
We also confirmed that fossil pollen grains could be extracted from not only lacustrine deposits, but also peat and volcanic soils. The extraction method can be applied to a range of terrestrial sediments deposited in various environments. Combined with Bayesian modeling, radiocarbon dating of strategically chosen horizons can provide much stronger age constraints to event deposits such as volcanic ash and tsunami deposits.