Prospect of direct AMS radiocarbon dating of pollen concentrates in ice wedges

Different approaches and techniques for the extraction of pollen and spores in the studies of palynologists who dated pollen concentrate from sediments of various origins are considered. The results of dating of spore-pollen concentrate in lake sediments of Lake Baikal, New Zealand, in sediments of the lakes Yellowstone, Mondsee, Van, Suigetsu, in loess deposits of China, in tropical peatland on Kalimantan Island, and in the peatland in the vicinity of the prehistoric settlement of Nunallek are reviewed in southwest Alaska. The results of the dating of pollen concentrate and spores in the ice wedges in the north of Western Siberia and the lower reaches of the Kolyma River are presented. It has been shown that although pollen and spores are contained in all permafrost objects without exception, their concentration is often very low in both ground ice and host sediments, especially in the ice. A technique for separating pollen and spores from ice for AMS radiocarbon dating has been developed. A specially developed sample preparation procedure for extracting pollen from ice veins makes it possible to extract sufficient amounts of pollen and spores for AMS dating from samples ranging in volume from 30 to 1 liter. The application of the cytometry method based on the use of the fluorescence characteristics of pollen and spores to obtain a pollen dating concentrate is considered. This modern method makes it possible to obtain an exceptionally pure concentrate containing pollen and spores without organic impurities. The results of radiocarbon AMS dating of pollen concentrate extracted from syngenetic Late Pleistocene ice wedges of the Seyakha and Bison yedoma deposits, together with the pollen spectra and the results of radiocarbon AMS dating of other organic fractions from the same samples, showed that microorganic fractions of more than 200-400 microns are often the most reliable. However, if the pollen concentrate contains pollen and spores deposited exclusively in situ, then radiocarbon dating of the pollen concentrate is the most accurate date. The dates of the pollen concentrate are in good correlation with the ratio of allochthonous and autochthonous pollen in the ice samples. However, the thresholds affecting the assessment of the reliability of the dating of pollen concentrate vary by region.