Climate And Environment Changes In The Late Holocene In Northeast China And Their Possible Effects On Paleoanthropological Society

Northeast China is one of the cradles of ancient Chinese civilization.During the Holocene,it has experienced multiple cultural types,and has abundant cultural sites and archaeological materials.It is an ideal area to study the influence of climate change on the rise and fall of paleoanthropological society.It is also a sensitive area for global change.However,due to the poor continuity and low resolution of the existing palaeoclimate data,the study on the relationship between climate change and evolution of paleoanthropological society is still in the qualitative description stage,and the evidence of high-resolution quantitative palaeoclimate records is lacking.In this background,this paper took Jinchuan peatland of Huinan county in Northeast China as the research object,and used gas chromatography-mass spectrometry?GC-MS?and high performance liquid chromatography-mass spectrometry?HPLC-MS?to analyze and test the biomarkers.On the basis of reliable AMS¹⁴C dating,the distribution and combination characteristics of n-Alkanes and GDGTs were analyzed systematically to analyze the climatic and environmental information of Jinchuan peat in the late Holocene and reconstruct high resolution temperature changes in the late Holocene quantificationally.At the same time,climate and environmental changes and their possible impacts on paleoanthropological society are analyzed by combining historical records and archaeological data.The main results of this paper are as follows:?1?The distribution range of n-Alkane in Jinchuan peat is nC₁₅?nC₃₃,most of which take nC₂₇ as the main peak.Medium and long chains have obvious odd over even predominance.CPI values ranged from 2.79 to 16.03,with an average value of about 5,indicating that the main input sources of higher plants are significant.?2?n-Alkane P_aq can generally respond to the change of humidity in the late holocene,but the P_aq value in the profile is relatively high in the whole Jinchuan peat.The P_aq value fluctuates about 0.5 or more,which may mainly indicate that the peat bog is dominated by the input of submerged and floating plants,and the water level is relatively high.Moreover,the peatland are developed in a stagnant environment,so the P_aq index may not be able to respond sensitively to regional or local climate and environmental changes.When the value of ACL is low,the corresponding annual average temperature is low.It is preliminarily speculated that ACL in Jinchuan peat may be significantly affected by temperature.The higher CPI value in the whole sequence indicates that the higher plant input may not be significantly modified by microorganisms during the development of Jinchuan wetland,which also indicates that the modification of organic matter in peat deposition is weak.?3?Variation trend of ratio of n-alkane C₂₇/C₃₁ and C₂₇/C₂₉ are completely different from P_aq and other index,which indicates that the n-Alkanes have different responses to climate,environment and even biological changes in Jinchuan peat.Pollen records indicate that the input of regional vegetation may cause a large change in the ratio of C₂₇/C₃₁ and C₂₇/C₂₉.However,we also found that the high values of C₂₇/C₃₁ and C₂₇/C₂₉ mostly correspond to the low average annual temperature reconstructed from the distribution characteristics of b GDGTs on the branch chain of soil bacteria.Thus,these n-Alkane ratios may reflect large vegetation?herbaceous or woody inputs?or/and climate change.?4?GDGTs compound is widely distributed in Jinchuan peat,and the content of bacterial b GDGTs is much higher than that of archaea i GDGTs.The main i GDGTs compounds is GDGT-0,and the contents of Cren and Cren'are the lowest.The content of Ia,IIa,IIa'and IIIa in b GDGTs compounds is the highest,followed by the content of IIIa',IIb and IIb',and the content of other compounds is very low.?5?The global peat CBT-MBT temperature correction formula was used to quantitatively reconstruct the annual average temperature change of Jinchuan peat in the past 3600 years,with a range of about 11?.Three cooling events were found,1720 BC?910 BC,870 AD?1080AD and 1580 AD?1680 AD.Volcanic eruptions have been recorded in two periods.Volcanic eruptions may cause short-term cooling and change of sedimentary environment at the same time,which may lead to changes in the living environment of bacteria and thus affect the change of MAAT_peat value.The fluctuation of about 7-8?in the upper part of Jinchuan peat may be influenced by seasonal factors,which makes the average annual temperature slightly higher.?6?The pH and IR_6me sequences reconstructed by b GDGTs have good consistency with the relative humidity sequences:the decrease of relative humidity between 1550 BC and 1000BC and between 860 AD and 1060 AD can better explain the formation of the dry environment,and these decreases of humidity just correspond to the low value of MAAT_peat.?7?The low temperature,decreased rainfall and drought in the late Holocene period from1550 BC to 1000 BC,from 860 AD to 1060 AD and from 1580 AD to 1680 AD may have led to the disappearance of the Lower Xia Jiadian culture,the collapse of the Tang dynasty,the chaos of the Five Dynasties and Ten Kingdoms,and the collapse of the Ming dynasty.