Environmental Changes And Human Activities During The Early MIS-2 Period In The Northeast Part Of North China Plain

Marine isotope stage 2?MIS-2??29-14 cal.kyr BP?represents the period of coldest temperature and maximum glacial extent within the last glacial period.During MIS-2,the Earth had experienced a dramatic drop in worldwide sea level,significant reductions in sea surface temperature and solar radiation,and sustained expansion of ice sheets until the last glacial maximum?LGM?began.In this period,several abrupt climate changes similar to Heinrich events occurred and deeply influenced human evolution.The Zhaocun Ruins in eastern Hebei province is not only the first Upper Paleolithic site found in the southern foothills of Yan Mountains,but also a type locality of Upper Pleistocene strata and fossil fauna.However,relevant environmental studies at relatively low resolution and lack of an absolute chronology.The present study reveals the characteristics of environmental changes and the background of human activities in eastern Hebei province during early MIS-2,which dating the profile fron 27.8-24.3 cal.kyr BP,through AMS¹⁴C dating of seven samples,a high-resolution pollen analysis,Carbon concentration analysis and a particle size analysis.The background of human activities and the characteristics of environmental changes in the early stage of MIS-2 in this region are revealed.The results showed that:The results shows that the pollen assemblages characteristics indicate that the region's vegetation was meadow steppe dominated by Artemisia and Asteraceae during the duration of microlithic culture?27.8-26.6 cal.kyr BP?,the relatively high mountains nearby were covered with Picea forests.Carbon dust the dust density is low,the entire profile to local fire,total concentration in?2211-8039?fluctuations between grain/g^-1,coarse grain charcoal dust concentration appears two small peak,coarse coal dust concentration showed that carbon dust handling the closer distance,the greater the local local fire appeared twiceThe deposit in this period is comprised mainly of silt,dark in color,which imply a quasi-hydrostatic boggy sedimentary environment.These exhibit the highest biodiversity and warmest climate in this profile,but the overall climate was colder and drier than it is today.In order to adapt to increasingly deteriorate and unstable environmental changes,humans of this period made alterations to the means whereby they lived,such as changing the types of stone tools and broadening their food choices.The upper cultural deposits?26.6cal.kyr BP?signify that the whole Earth entered the early LGM,the percentage of Picea pollen and fern spores and the content of fine particles increases rapidly,especially peaking in profile from 26.2-25.5 cal.kyr BP,which suggesting a much colder and wetter climate than before and the presence of a Picea forest nearby,indicating that the deposit formed in a lacustrine environment.The density of carbon chips was significantly increased,and the fluctuation was more significant.Regional fires started to increase,and the total concentration fluctuated between?1153-26953?grains/g^-1,reaching the maximum of the entire section.It follows that the study area underwent a cold-wet event during 26.2-25.5 cal.kyr BP,which may corresponds to the third glacial stage in the D/O cycles.The cold and moist climate led to a drastic decline in local biodiversity,thereby intensifying the food shortage.Moreover,the spaces where human activities took place were gradually flooded due to the rising river level,forcing them to relocate.Therefore,there is a break in the cultural deposits.The percentages of Chenopodiaceae,Poaceae and Cyperaceae pollen from 25.5-24.3 cal.kyr BP substantially increase,while the Picea pollen and fern spores significantly decrease.The corresponding concentration of carbon chips decreased in the previous area,and the total concentration fluctuated between?1174-11445?grain/g^-1,and the regional fire increased.This indicates a vegetation pattern characterized by meadow or meadow steppe.The corresponding deposit,with coarser particle size,comprises interbedded clay and fine sand,which indicate that the study area became drier and a typical floodplain deposit.The pollen assemblages from 24.3-23.6 cal.kyr BP is dominated by Artemisia,Asteraceae,Chenopodiaceae and Poaceae and the deposit shows the coarsest particle sizes and highly variable composition.The total concentration of carbon aggregates fluctuated between?730-2936?grain/g^-1,the lowest in the whole section,and the most regional fires.This period represents the coldest and driest period recorded in this profile,which possible corresponds to event H2.