Phytolith Paleovegetation And Paleoclimate Process Since Mid-Holocene In The Middle And Lower Reaches Of East Liaohe River

Global change is one of the main challenges facing mankind at present.Exploring past climate changes can predict future climate change patterns and provide scientific guidance for the sustainable development of human society.Northeast China is an ideal area for paleoenvironment restoration and global change research.However,little attention has been paid to this area in the early research,and the indexes used by scholars are limited,and regional high-resolution climate data are relatively scarce.In this paper,we take the soil profiles of Wukecun and Dafuling in the middle and lower reaches of the East liaohe River Basin as the research objects,use AMS¹⁴C and OSL dating methods to establish the profile age frame,and conduct the extraction and identification of phytoliths of soil samples and analysis of combination characteristics.Combining magnetic susceptibility,loss on ignition,chromaticity,and particle size methods to assist in verifying the paleo-vegetation paleo-climate results retrieved by phytoliths,reconstruct the paleo-vegetation process since the Holocene in the region,and then reverse the paleo-climate process.The main results of this article are as follows:1.According to the analysis of phytolith assemblage characteristics and paleo-vegetation index,the study area has been a grassland community since the Mid-Holocene,(1)About 7300-6600 a B.P.,the coverage of woody plants increased,and the number of Eragrosinae and C3 plants was medium;(2)About 6600-5600 a B.P.,the fluctuation of woody plant coverage increased,and the number of Eragrosinae plants increased,and there were fewer C3 plants in general;about 5600-4100 a B.P.,the woody plant coverage of Wukecun section fluctuated more,and there were more ragrosinae and C3 plants in Dafuling section;about 4100-3100 a B.P.,The coverage of woody plants has increased overall,and the number of Eragrosinae and C3 plants in Dafuling section was higher than that of Wukecun section;(3)About 3100-1100 a B.P.,the coverage of woody plants has decreased,Eragrosinae and C3 plants increased;about1100-300 a B.P.,woody plants had no obvious change trend,Eragrosinae and C3 plants decreased.2.Combining the indicators of magnetic susceptibility,loss on ignition,chromaticity,and grain size on the magnetic material,organic matter content,formation conditions,and sedimentary environment of the sediment,the climatic process inverted by the phytolith paleoclimate index is verified,and the two sections are compared and analyzed.(1)About 7300-6600 a B.P.,the climate was cool and the humidity was moderate;(2)About 6600-5600 a B.P.,the climate was mild,and the overall climate was slightly humid;about 5600-4100 a B.P.,the climate was cool and the humidity was slightly lower,and the climate in Wukecun section was cooler;about 4100-3100 a B.P.,the climate was mild and slightly wet;(3)about 3100-1100 a B.P.,the climate was mild and slightly dry;about 1100-300 a B.P.,the climate was warm,with increased humidity and slightly humid.3.Comparing the obtained paleoclimatic process of the study area with solar activity index,Liaoning Nuanhuodong stalagmite?¹⁸O,and major volcanic events in Northeast China,it is found that the degree of regional dryness and wetness responds well to monsoon activities.It is speculated that the paleo-vegetation and paleo-climatic process of the study area is mainly affected by the strength of the East Asian summer monsoon.It is found that the overall temperature rise in the region corresponds to the increase in solar radiation.Based on this,it is speculated that solar activity also has a certain impact on regional temperature changes.The above results use the phytolith index to initially explore the paleo-vegetation paleo-climatic process at the junction of the Songnen Plain and the Liaohe Plain since the Mid-Holocene,and obtain good regional response,which has certain significance for improving the research data of the paleoclimatic process in the region.