Spatiotemporal Changes Of Holocene Moisture Across Northwestern China And Regional Prehistoric Human Activities

The Holocene is the modern interglacial period starting from 11,700 years ago.Holocene climate change is closely related to the development of human society and thus it is an significant geological period to study human-environment relationships.The arid and semi-arid area in northwestern China is an important area of the ancient Silk Road,where the ecosystem is fragile and sensitive to climate change.Its geological archives are less affected by human activities,which make it an ideal area to study the changes of paleoclimate,paleoenvironment and the interactions between human activities and environmental evolution in historical period.Climate?especially humidity?change in the region has profoundly affected the ecological environment,human activities and social economic development in northwest China.In recent years,the results of high-quality climate proxies and and radiocarbon dating data of archaeological sites have been continuously accumulated.Therefore,it provides a chance to carry out a comprehensive research in a larger space,together with the latest new records and previous results of climate change and archaeological investigations to explore relationships between regional climate-environmental changes and the intensity of human activities.Studying the spatiotemporal changes of humidity in inland arid and semi-arid regions will help us to cope with environmental changes and human survival challenges brought by climate change now and in the future,thus to achieve sustainable development.This can provide a scientific reference for the country's"the Belt and the Road"and the Western China Development Strategy.This study selected 56 records from loess,lake,peat,tree ring and stalagmites in arid and semi-arid areas of northwestern China?Xinjiang,western Inner Mongolia,midwestern Gansu and northern Qinghai provinces?,including paleoclimatic alternative proxies with clear indication of humidity such as spore pollen,tree rings,loess-paleosol magnetic susceptibility,carbon isotope,and stalagmite oxygen isotope,etc.Each reconstructed paleo-humidity sequence was linearly interpolated for the same time resolution,then we used the regional average method for integrated analysis of humidity series since Holocene,and regularization method for humidity series since one thousand years ago.In order to analyze the Spatiotemporal changes of humidity in the area,inverse distance weighted method is used to separately interpolate the humidity levels in two periods on the scale of millennium and centenary.In addition,this paper collected and explored 820 published ¹⁴C dating data from 235 archaeological sites in this region to reveal the characteristics of spatial distribution and quantity changes of the sites and to reveal the regional human activities by generating a cumulative probability density curve of ¹⁴C data of the dataset.The main conclusions are listed as follows:?1?The humidity in the arid northwestern region of China generally showed a rising trend with fluctuations since the Holocene,that is,the early-Middle Holocene was drought,then the Middle Holocene became wet,and the late Holocene was the wettest.Among them,the humidity in Xinjiang is similar to the change trend in the general study area,and its humidity level has changed significantly,while the humidity integration curve in eastern part of study area?Asian monsoon marginal area?has a small change range and no obvious change trend.There are obvious regional spatial differences in the Holocene humidity,especially in the marginal areas of the monsoon.This may be related to the extent of Asian monsoon penetrates inland,the influence range of the westerly circulation and topographical factors.?2?Over the last one millennium,the humidity in the study area was fluctuating with a declining trend.The humidity in Xinjiang was generally rising with fluctuations,whereas the eastern part of study area is declining with fluctuations.The humidity in the study area showed obvious regional characteristics.Among which the spatial differences in humidity of Xinjiang has been significant since the millennium,while the spatial difference in humidity levels in eastern part of the study area has been significant since the past 500 years.?3?The integrated humidity curve in Xinjiang is in good agreement with the accumulated probability distribution of ¹⁴C dates indicated human activities,and the humid climatic condition is one of the main factors that promotes the increasing of the intensity of human activities.However,the integration curve of humidity in eastern study area does not change significantly,and the spatial difference is complicated.The relationship between humidity and human activities is also more complicated.It is suggested that regional climate fluctuations promoted human migrations and technological exchanges and diffusion,which in turn increased human capacity to adapt to environmental changes.