AMS ¹⁴C Ages Of The Pollen Concentrates And The Holocene Climate Changes Documented By Barkol Lake

The record of lakes sediment is a good and effective carrier to study past climate changes, especially in arid and semi arid areas where there is lack of high-resolution records relatively. However, due to the impact of the "reservoir effect" of lakes, there are always some errors during the processes of establishing a chronological sequence, which makes it difficult to research the paleoclimate.14C dating is one of the primary methods in dating lake sediments. With the further study of the Holocene climate changes, the higher-resolution dating of lake samples plays a more and more important role in the lake studies, whereas different 14C dating methods make different errors.To explore more reasonable ways of 14C dating of the lakes in arid areas, based on some sample of Barkol Lake, this study compared the pollen concentrates for AMS 14C dating, with the whole sample analysis method for 14C dating and the terrestrial higher plant residues for 14C dating. Our dating results show that AMS 14C ages of the pollen concentrates are consistently 780 years younger than the whole samples in the same layer, which is similar to the "carbon pool" effect calculated through the 14C ages of whole samples subtract the 14C ages of terrestrial higher plant residues; the AMS 14C ages of the pollen concentrates is very close to the 14C ages of terrestrial higher plant residues, implying that the pollen concentrates can be expected as reliable dating material in the dating process of the lake sediments in arid areas.A high-resolution proxies record from the sedimentary cores of Balikun Lake, combined with reliable chronology, is used to reconstruct the history of Holocene vegetation and climatic change in the study area. The climate environment was ameliorative in 8.8～7.9 cal. kyr BP. The study area was desert steppe/steppe in middle Holocene (7.9～4.3 cal. kyr BP), and the effective humidity was improved dramatically, the climate environment was the optimum, while the adjacent upland of lake might grow Patch Birch Forest. The vegetation of study area changed form desert steppe/steppe to desert vegetations in the ephemeral period 4.3～3.8 cal. kyr BP. The effective humidity was decreased, and there might be a century arid climate event. There was a typical desert steppe/steppe scene in later Holocene (3.8～0.53 cal. kyr BP), and the effective humidity was improved dramatically. The desert vegetation appeared since 0.53cal.kyr BP. The comparison results of different areas appeared that the climate environment evolution in study area was different from the area controlled by the East Asian monsoon. The period of Last Glacial-Early Holocene was dry, while it was more humid in mid-later Holocene.