Relationship Between Climate Change And Cultural Evolution In The Loess Plateau Since Mid-late Holocene

Since the middle Holocene,the human culture has entered a period of prosperity with the development of Neolithic agriculture.The boundary conditions of the mid-late Holocene climate system didn't change significantly compared with the glacial-interglacial period,and the regional paleoclimate records are rich.The mid-late Holocene climate change is one of the research hotspots in the international community,so it's highly valued by scientists.Different scholars have different understandings on the climate change of the mid-late Holocene in arid and semi-arid regions of China.Therefore,more reliable climate records are needed to further understand the climate change.The Loess Plateau,located in the semi-arid region,is a monsoon edge region,which can respond to climate change quickly.Moreover,the Loess Plateau is one of the Neolithic culture core areas in China,which has a continuous Neolithic cultural sequence.Understanding the climate history in this area is helpful to understand the relationship between climate change and cultural evolution.In this paper,two lakes in the Loess Plateau are selected as the research objects.They are Tianchi Lake of Liupan Mountains which is not easily affected by human activities and Gouchi Lake which is easily affected by human activities.Based on the analysis of?D(?D_l,?D of leaf)from GSA07 of Tianchi and TOC,TN,?¹³C_org,?¹⁵N_orgfrom GC15B of Gouchi,combined with the reliable AMS¹⁴C chronological sequence,we reconstruct the climate change of the Loess Plateau since the mid-late Holocene.In addition,this paper discusses the relationship between climate change and cultural evolution and dynasty replacement,and preliminarily analyzes the driving forces of climate change.The main conclusions are as follows:(1)Based on the analysis of?D and?¹⁸O in leaf of Abies from GSA07 in Tianchi,it is found that the?D_l reflects the change of Indian summer monsoon intensity.The negative?D_l indicates an increase in the monsoon and the positive?D_l indicates a decrease in the monsoon.The result shows that the monsoon intensity decreases gradually.The monsoon intensity is stronger during 6200?4000 cal BP,and the weakening trend is not obvious.After 4000 cal BP,the monsoon intensity is weaker than the previous stage,and shows a gradually weakening trend.(2)Based on the study of TOC,TN,?¹³C_org and?¹⁵N_org,C/N of GC15B in Gouchi,we found that the input of terrestrial plants is the main source for Gouchi.When the climate is wet,the regional biomass is large and the nutrient level is high,TOC,TN and?¹³C_org increased,lake productivity increased,¹⁴NO₃^-was largely consumed,?¹⁵N_orgincreased;conversely,TOC,TN,?¹³C_org and?¹⁵N_org decreased when the climate is dry.Combined with the core chronology,the results show that the regional climate is becoming dry gradually during the period of 8130?2400 cal BP;after 2400 cal BP,human activities significantly affect the hydrological conditions of the lake with the increase of regional population.(3)Taking Tianchi and Gouchi as examples,this paper discusses the relationship between climate change and cultural evolution.The results show that the period of cultural transformation often corresponds to the period of monsoon weakening/dry climate,the mid-term period of culture and dynasty prosperity roughly corresponds to the monsoon strength/wet climate.In general,climate change may plays an important role in cultural development and dynasty replacement.(4)Based on the India summer monsoon history in the past 6200 years,we discussed the driving mechanism of climate change.On the orbital scale,the Northern Hemisphere Solar Insolation(NHSI)is the main factor affecting the intensity of Indian summer monsoon.The increase of NHSI makes the monsoon stronger,while the decrease of NHSI makes the monsoon weaker.On the sub-orbital and centennial scale,solar activity may affect the monsoon.Solar activity increase,the monsoon strengthens,and solar activity weakens,the monsoon weakens.