Study On Climate Change Of High Resolutionrecords From The Stalagmite In Early Holocene

In the context of the rapid development of world economy,global warming has been an incontrovertible fact.The study on climate stability and prediction is particularly necessarywith respect to the intensification of greenhouse effect and frequent appearance of extreme weather events.Nowadays,human society is in the Holocene,a modern period with warm climate,and it has been for more than 10,000 years.The emergence of human civilization,social development and economic prosperity are all in this period,and the prosperityorrecession of human civilization seems to have a potentialrelation with climate change.As the present research shows,the Holocene climate change is not stable in Asian monsoon region,and there are several weak monsoon events in it.However,most of the previous studies have focused on the overall trend of monsoon and its forcing mechanism.And the discussion about weak monsoon events are mainly focused on 4.2kyr BP and 8.2kyr BP events,while,there are less researches on the shorter scale climate change mechanisms,especially in early Holocene.As an important geological carrier for paleoclimatic reconstruction,high-resolution stalagmite record has attracted more attention from academia.We establish an accurate age scale based on 11 age data of Yangkou cave stalagmite YK719,and we better understand the record of stalagmite to the outside climatic environment by the analysis of carbon and oxygen stable isotopes,trace elements and gray scale data.In order to study the climate change in early Holocene,we compare YK719 with other contemporary geological records.The correlation between YK719 and North Atlantic SST,Intertropical Convergence Zone(ITCZ)and sunspot number arecarried out,moreover,the power spectrum analysis is also implemented.All above make it possible to discuss the forcing mechanism of climate change inearly Holocene and the Asian monsoon fluctuation.Conclusion as follows:(1)The?18O record of stalagmite YK719 from Yangkou cave exhibits :·Thefluctuation range of oxygen isotope value:-7.1 ~-8.7‰,and average value is about-7.9‰.The ?18O records the11.1 and 10.3kyr BP event corresponding to the Bond8/7 event when the climate experienced a "cold-warm-cold" transition,which is also recorded in some other Asian monsoon caves.?During 10.3 ~ 9.7kyr BP,?18O suddenly drops from-8.7‰ to-9.5‰ with average value is about-8.7‰.Compared with previous stage,oxygen isotope is apparently more lighter and the time span is short in this stage,indicating that the climate in the region experienced fast enrichment of monsoon after a cold event,which resulting in rapid depletion in oxygen isotope,and also responds to the fast northward movement of ITCZ.? During 9.7 ~ 8.3kyr BP,?18O value fluctuated between-8.3‰ and-11.1‰,and the average is about-9.7‰.Stalagmite ?18O abruptly decreases from 9.7kyr BP,then it consistently drops.Compared with the first two stages,?18O in this period is the lightest in early Holocene and it has been found in stalagmites in other Asian monsoon caves.It proves that the Asian monsoon climate,as a whole,set in a warm and humid period due to the increase of solar radiation.(2)We compare the carbon isotope,grayscale of YK719 with SST in high latitude of North Atlantic and Ti concentration of Cariaco Basin records in low latitude,and find that ?13C and grayscale show a good correlation with the North Atlantic SST in the weak monsoon period,indicating that ?13C and grayscale are controlled by monsoon and the North Atlantic Ice Rafted Detritus(IRD)events.The response mode of ?13C and gray scale to temperature:Due to the increase of temperature,the surface vegetation biomass would soar up.The increase of microbial biomass in soil couldreinforce the humus decomposition ability,as a result,the yield of CO2 in soil would increase and the ?13C value of soil CO2 become light.Meanwhile,the calcite deposition is pure,transparent and dark,which affects the optical characteristics and results in the decrease of the grayscale value.Under the cold and dry condition,on the contrary,the surface biomass decrease and the ?13C is heavy.There are more impurities in the stalagmite,which makes it white and gray.Strong evaporation and less precipitation would promote more impurities into the stalagmite lattice and lead gray scale value increase.(3)The gray scale of YK719 grayscale records cold climatic events in early Holocene,and it is closely related to solar activity.The ?13C and the grayscale have a good correlation,indicating the grayscale might be related to the external vegetation and soil microbial activity,but there is a certain difference in the overall trend changes.The gray scale does not show a palpable change but the ?13C of YK719 becomes lighter consistently.It is possible that the sensitivities of the two recordsto forcing factors are different.The gray scale is particularly sensitive to changes in solar activity whilst responding to precipitation and temperature,resulting in suppression of other record signals.The change in gray scale value is closely related tosolar activity.When the solar activity is strong,the gray scale value is low,otherwise it is high,which might be related to solar radiation.(4)We found that there is solar activity cycle in the stable oxygen and carbon isotopes and gray scale value by using power spectral analysis,which denotes that the evolution of Asian monsoon is mainly affected by the solar activity on a short time scale and is force by the solar radiation energy.Meanwhile,when analyzing the grayscale with the same method,we found that not only the solar activity but also the Western Pacific subtropical high pressure may have impression on the Asian monsoon.