Peat-based Late Holocene Climatic Reconstruction In Pamir Plateau,Centralasia

Extreme climatic events have been more frequent and violent in recent years,which has had a negative impact on our society’s development.Climatic change is now one of the top environmental concerns that is receiving increasing attention.Future development will greatly benefit from identifying the factors influencing climatic change and formulating effective strategies.“Understanding the past is essential for predicting the future”,a sufficient understanding of past climatic change is a prerequisite for making reasonable predictions and developing responsive strategies for future climatic change.Paleoclimate research records a long-term and continuous history of climatic change,considerably extending the instrumental records of the present climate,and provides information on regional and seasonal climatic change.Due to its delicate natural habitat,the Pamir Plateau,which sits in the core area of the Arid Central Asia,is especially vulnerable to climatic change.Compared to the surrounding areas,there are relatively few studies on the climatic change of the Pamir Plateau during the Holocene,and previous research mainly focus on humidity variation（or precipitation）.In this study,we focus on a peat sequence in the Tagharma Plateau Wetland and used 7 AMS ¹⁴C dating to establish the chronological framework.Multiple proxy(LOI,grain size,humification,δ¹³C_α-cellulose,and n-Alkanes)are used to reconstruct the climatic change during the Late Holocene.The main conclusions are as follows:（1）The organic carbon isotope(δ¹³C_org)of topsoil in the Pamir region exhibits a positive correlation with temperature(i.e.,a higherδ¹³C_orgindicating a warmer climate).In Taherman Wetland,δ13C_α-cellulossand ACL of the peat core are positively correlated with temperature,P_aqdenotes a shift in humidity.But the amount of precipitation in the area is lower,P_aqprimarily denotes the dry and wet changes of the internal microenvironment of the wetland.The humid environment may indicate the increase of ice and snowmelt water caused by high temperatures,and the arid environment may also indicate that the evaporation caused by temperature rise is greater than the water vapor supply.A wetland with favorable hydrothermal conditions has lower CPI and LOI values,higher levels of humification,stronger microbial activity,and more organic matter that decomposes but accumulates less.（2）Multiple paleoclimatic data sets from the region suggest a warming and drying late Holocene which can be further divided into three phases:Stage I（approximately 5000～3600 cal.a BP）.Microorganism activity steadily increases in a cold and dry environment,peat breakdown is vigorous and the amount stored is small,sediment grain size is relatively fine,and the deposition rate is relativety low.The lowest temperature in the Late Holocene occurred at 3600 cal.a BP,and the"4200 year cold event"may be related to the significant low values of LOI and CPI at around 4200 cal.a BP.StageⅡ（approximately 3600～550 cal.a BP）.The climate changed from a cool and dry to a warm and dry.The amount of glacial melt water has increased as a result of climatic change,and humidity levels briefly increased（approximately 3600～3300 cal.a BP）.As a result,as the range of glaciers shrinks and evaporation rises,the temperature continues to climb.Wetlands’relative humidity drops,microorganism activity changes drastically,the amount of humification reduces,organic matter decomposes less and accumulates more,the particle size of the sediments grows,and the rate of deposition quickens.StageⅢ（approximately 550 cal.a BP to the present）.The Little Ice Age（approximately 550 to 200 cal.a BP）was evident from multiple proxy data sets(such as LOI,δ¹³C_α-cellulose,and n-Alkanes).After the Little Ice Age,temperatures rose and humidity increased,causing peat to have coarser grains and deposit more quickly.（3）Preliminary driving mechanism analysis shows thatthe decrease of summer solar between approximately 5000～3600 cal.a BP immediately causes a decline in temperature.The decline in temperature in the early Late Holocene may possibly have been brought on by the westerly jet’s southern shift,which was brought on by a reduction in summer solar radiation in the Northern Hemisphere.With the advancement of agriculture and animal husbandry,as well as the expansion of human activities,the globe’s population has expanded since the late Holocene,or the middle of the Bronze Age（approximately 3600 cal.a BP）.The temperature drop brought on by a decrease in summer solar radiation has been outweighed by the global warming brought on by an increase in anthropogenic greenhouse gases.Additionally,it’s possible that the general trend of the Tahman Wetland drying in the late Holocene was brought on by the fact that the temperature shift overpowered the local humidity change,which led to an increase in evaporation that dried out the wetland.