Paleoclimate Study Of The Peat Profile Recorded By Phytolith In The Northern Dunhua Basin Over The Past 2000 Years

The past two thousand years included the climate change phases which was dominated by natural variability before ca.1800A.D.,and the the one with both human activities and the natural environment since the last 200 years.The climate change research covers a wide range of topics.The prediction of future climate and environmental changes has far-reaching significance.At this stage,based on the development of human historical civilization and the evolution of the environment,a large amount of historical documents and natural environment carriers have been preserved,which provides a sufficient source of data for paleoclimate reconstruction.Among them,the Medieval Warm Period and the Little Ice Age are the most recent and most significant global climate change stages.The research on their start and stop time,temperature and humidity pattern,and climate-driven mechanism have become important topics in the field of paleoclimatic paleoclimatic research.An irreplaceable position.Dunhua is sensitive to climate change with complex climate change.In this paper we choose the mountain peat in the north of Dunhua basin as research object,selects the appropriate sample for ¹⁴C dating,and establish the time-depth curve to to construct a complete chronological framework by Bacon model.Taking peat samples at every centimeter analysis phytolith for high-resolution,and choosing the appropriate phytolith index to reconstruct the climate environment in recent 2ka of studied area;discussing the formation of peat in studied area with the combination of magnetic susceptibility and particle size index;describing the characteristic climate period and exploring the climate formation mechanism in recent 2ka of the studied area basing on a comprehensive comparison of other research results.The specific results are as follows:1.According to the changes of phytolith combination and the results of cluster analysis,the climate process of the peat profile can be divided into four stages:?1?In ca.45⁶80A.D.the climate was warm and humid with obviously fluctuation;?2?ca.680¹340A.D.it was warm and dry,with a tendency of turning cold and dry;the Medieval Warm Period?MWP?appeared during ca.680¹225A.D.;?3?ca.1340¹870A.D.,showing the climatic characteristics of the small glacial period?LIA?,with the character that it was cold and dry in the early and late period and wet in the medium term;?4?ca.1870²017A.D.it was warming up,the environmental changes may be affected by human activities,and the degree of interference in which still needs further study.2.After analyzing various indicators,it was believed that the accumulation process of peat in the studied area was superimposed by wind and surface runoff,and the peat deposition was represented by lake phase.When it's wet,the carrying capacity of surface runoff increased and the wind transportation weakened,and peat deposition was mainly dominated by surface runoff.When it was dry,the effect of water weakened,at which point the coarse particles in peat may indicated dust events.The magnetic susceptibility of the profile consisted well with the phytolith temperature index,indicating that the source of magnetic material in peat was dominated by autogenous transformation,the magnetic susceptibility increased with a increase of temperature,on the contrary,the magnetic susceptibility decreases.3.Charcoal and burnt phytoliths had good indications for fire events.High temperature and drought environment and volcanic activity are the main causes of fire events.The occurrence of fire events in the past 200 years may be closely related to human activities.4.Comparing the phytolith indexes in the studied area with the solar activity cycle and the solar radiation flux curve,it was found that the temperature variation in the study area is affected by solar radiation.When the solar radiation flux is large,it corresponds to a warm period,and when the magnetic flux is small,it corresponds to a cold climate.Solar activity had a significant impact on the hydrological conditions in the studied area.It was dry during the great solar maximum,the climate is dry,and there was no obvious characteristic of dry and wet in the solar minimum.5.Comparing the phytolith index of the studied area with the stalagmite?¹⁸O curve and the Ni?o 3.4 index,it was found that the drought index and the?¹⁸O curve responded well,indicating that the precipitation change in the studied area was regulated by the East Asian summer monsoon.Compared with the Ni?o 3.4 index,it was found that it was in the La Nina-like condition during the Medieval Warm Period,with dry climatic conditions,and in the El Ni?o-like state corresponding to a long wet period during the Little Ice Age.The changes in the climatic environment of the studied area in the past 2ka responded well to past global changes and were of great significance in studying the regional differences in global change.