| Studying the law and mechanism of climate change in inland arid areas of Xinjiang and the impact of regional climate change on the evolution of human society can improve our understanding of climate system dynamics and provide insights for predicting future climate change and accessing the relationship between climate change and civilization evolution.In this paper,the peat profile of Taheman(THM)wetland in Tajik Autonomous County of Xinjiang was recovered.Under the support of reliable AMS14 C dates,vegetation and climate change in Taheman area were reconstructed by high-resolution pollen records since 4900 cal.yr BP(BP = before present,where present is AD 1950).Furthermore,we discussed the climate pattern and possible dynamics of climate change,and explored the periodicity of climate change in THM region using Redfit spectral analysis and Morlet wavelet analysis.In addition,we discussed the impact of climate change on the evolution of human social civilization in Xinjiang through the comparison of our THM climate sequences with the radiocarbon dates-recovered human activities history.The main results of this study are as follows:(1)The pollen reconstructed vegetation changes in THM area since the 4900 cal.yr BP includes 5 stages.During 4900 - 3540 cal.yr BP,Carex meadow developed in the THM river valley and mountain desert dominated by Chenopodiaceae and Ephedra,which might correspond to the current Sympegma regelii desert and Ephedra przewalskii desert prevailed in the nearby mountain.Between 3540 cal.yr BP and 1950 cal.yr BP,the desert dominated by Artemisia,probably similar to nowadays Artemisia rhodantha desert,expanded at the cost of the desert dominated by Chenopodiaceae and Ephedra in the regional mountainous area,the later was similar to the present Sympegma regelii desert and Ephedra przewalskii desert.At the meantime,the Carex wetland retreated,and the Salix shrub might have developed locally around the retreated wetland.During 1950 - 490 cal.yr BP,Artemisia rhodantha desert might extremely expand,and the distribution areas of Sympegma regelii desert and Ephedra przewalskii desert shrank,the Carex wetland retreated further,and the Salix shrubs almost disappeared in the valley wetland.During 490 - 190 cal.yr BP,the Carex meadow extremely expanded in the valley,the Kobresia-dominated mountain meadow might have developed in subalpine mountains of the watershed,and the desert of Artemisia,Chenopodiaceae,and Ephedra retreated in regional mountain areas.From190 cal.yr BP to now,the valley Carex wetland might shrink sharply,the Kobresia Meadow in the regional mountains might shrink sharply,the desert dominated by Artemisia in the regional mountains expanded extremely,and the mountain Chenopodiaceae desert might have also expanded.(2)The consistency among the THM pollen assemblages,the pollen-based principal component analysis(PCA),the Artemisia/Chenopodiaceae(A/C),and the Artemisia/Cyperaceae(A/Cy)suggest a reliable climate reconstruction.The PCA analysis results showed that PC1 might indicate the regional temperature and PC2 might indicate the regional moisture,which was consistent with the changes in temperature and moisture reflected by pollen assemblage,and the trend of pollen temperature proxy(A/Cy)and moisture proxy(A/C).As results,the THM area experienced a generally dry and cold climate during 4900 - 3540 cal.yr BP,a warming and wetting climate between 3540 and 1950 cal.yr BP,a generally warm and wet climate during 1950 - 490 cal.yr BP,a cold and wet climate during 490 - 190 cal.yr BP,and a warm and dry climate during past 190 cal.yr BP.(3)The pollen-based THM temperature sequence was comparable with the regional temperature sequence,indicating a generally increasing temporal pattern in arid Central Asia since the middle Holocene.The increasing might be forced by the positive feedback effect induced by the enhancement of GHG radiation forcing and human activities.At the same time,it was also driven by solar insolation(TSI).The results of Redfit spectral analysis,the Wavelet analysis,and the bandpass filter all displayed a remarkable periodicity of ?500 years,being consistent with The GHG ?500yr oscillation in the early stage,and the TSI ?500 yr oscillation in the later stage.The pollen-based THM moisture sequence was consistent with the regional moisture sequence,being supportive to the overall wetting trend in Arid Central Asia since the middle Holocene.The wetting climate might be caused by the increasing vapor transported by the westerlies under more negative phased NAO since the middle Holocene.Moreover,the rise in temperature caused the melting of glaciers in highaltitude mountains and thus increased the river runoff.At the same time,the warming led to the increase of evapotranspiration,which promoted the water vapor cycle and gradually increased the regional moisture.The results of Redfit spectral analysis and Wavelet analysis showed that the regional moisture fluctuation had a period of ?200-350 yr Since 4900 cal.yr BP.Bandpass filter results showed that the period of PC2 components imf2-imf3 ?200-350 yr was almost synchronous with that of NAO ?200-350 yr or lagging for decades.(4)The Pearson correlation analysis of the human activities proxy of SPD of Xinjiang with the temperature and moisture indices suggests that the SPD was significantly correlated with temperature and moisture at the level of p<0.01.The correlation between the SPD and the moisture index was better than that of the temperature index,indicating that moisture was a more important factor affecting regional human activities in the past 5000 cal.yr BP.The results of Redfit spectral analysis and Wavelet analysis showed that there were ?400 yr and ?200 yr cycles of human activities since 5000 cal.yr BP.Bandpass filter results showed that regional climate fluctuation was almost synchronous with human activity fluctuation during4000 - 1000 cal.yr BP.The cultural prosperity stages were consistent with the wet stages,suggesting regional human activities mainly responded to moisture change. |
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