The Reconstruction Of Climate Change And Soil Environment Since 86.5 Ka In The Gonghe Basin Based On The ML Profile

The Qinghai Tibet Plateau is a unique geographical unit in the world,it is also one of the regions sensitive to climate change.The study of paleoclimate changes will help to better understand the laws and evolution mechanism of climate change.The Gonghe Basin located in the northeastern part of the Tibetan Plateau is the East Asian monsoon marginal area,it is very sensitive to the evolution of the monsoon.Meanwhile,Gonghe Basin is also a region with obvious human activities on the Qinghai Tibet Plateau,the land desertification in the basin has seriously affected the production and life of local people under the combined action of natural and human factors.The study of environmental evolution will help people understand environmental changes better and formulate reasonable environmental response measures.This paper selected a profile of ML of the Gonghe Basin,this profile was composed of two aeolian sand layers,three loess layers and five loess layers.Combined with the 14 C dating results,and used the Kukla age model to calculate the chronological sequences formed at different depths.The calculated results are compared with OSL dating results.It is found that there is a hundred years' error between the estimated age of 14 C dating and the OSL dating result,the error is within the permitted range.Therefore,we obtained the sedimentary chronology of the ML profile since 86.5 ka.(1)Research results showed that the silt was the main grain size of sediment,followed by sand and clay.The grain size frequency curve of each profile was narrow and negative kurtosis.The main peak was prominent and there were multiple secondary peaks.The appearance of the main peak and the secondary peak was basically the same.It was indicated that the section was deposited under the common action of the strong dynamic proximal deposit and the weak power source sedimentation.The magnetic susceptibility of the sand layer was mainly affected by the cold period of wind transported into high susceptibility many xenobiotics influence,the magnetic susceptibility of loess layer was influenced by the number of high magnetic flux and the chemical weathering,the magnetic susceptibility of paleosol layer is obviously affected by chemical weathering(2)The variation coefficient of the oxide content of the constant elements in the ML profile was small,and the order was Ca O>Mg O>Si O2>Na2O,K2O>Al2O3>Fe2O3.Compared with Al element,Na,Mg and Ca showed obvious leaching,the leaching of Si,K and Fe was very weak.ML profile had completed the primary chemical stage of leaching Ca and Na.The profile showed the characteristics of rich Ca elements and poor Na and Mg elements compared with UCC.The content of the constant elements of the loess layer was similar to that of UCC,and the Ca O content in the wind sand layer and soil layer was significantly higher than that in UCC.In summary,the elemental characteristics reflected that the climate has been generally dry and cool since the profile was formed,and the weathering and soil formation has been weak.The climate was shifted to dry,alternating between cold and warm and wet during the period(3)The results of magnetic susceptibility reconstruction in profile sediments were more consistent with the actual situation.During the formation ML period,the annual temperature was-1.97~3.8 °C,the mean value was-0.84 °C,and the annual precipitation was 186.15~483.22 mm,with a mean value of 245.66 mm.The environment has been divided into three stages since the formation of the profile used the indicators of silt and clay content,magnetic susceptibility,content of Al2O3 and Ca O,and m of ML profile.The first stage,the climate changed cold and soil strength weaken in 86.5~78.9 ka BP.The second stage,the climate was relatively cold and dry,and the soil strength was weaker in 78.9~10.4 ka BP which belong to the last glacial period.This stage also was specifically divided into some secondary stages,including the period of cold-dry climate and weak soil strength in 78.9~60.0 ka BP and 22.3~15.0 ka BP,the period of cool-humid climate and stronger soil strength in 60.0~30.5 ka BP,the period of warm-humid climate and extremely strong soil strength in 30.5~22.3 ka BP,and the period of warm-dry climate and weak soil strength.The third stage,the climate was warm and dry,and the soil strength was achy since the 10.4 ka BP.This stage can be divided into three secondary stages,included the rapid warmer period of climate in 10.4~8.0 ka BP,and warm-dry climate period in 8.0~4.78 ka BP,and lesser warm-dry climate period since 4.78 ka BP.The soil strength experienced weaker-weakest-weak changes.(4)Compared with the environmental information revealed by the ML profile and the existing other profiles since the Holocene,we got the follow result.On the one hand,ML profile revealed that the environmental evolution of the Holocene has been divided into three distinct stages.That was consistent with the other research results,and it showed that the environmental changes in the region had global characteristics.On the other hand,the drought degree of the Gonghe basin revealed by this section was higher than that of other profiles.And the time span of three environmental evolution stages revealed by each profile was not the same,it showed that the environmental information reflected in this section had regional characteristics.