Instability Characteristics Of The Last Interglacial Period Recorded By Loess In Linfen Basin

Global climate change is one of the hot topics in geosciences.Among them,the climate instability since the last interglacial is the focus of global change research.The last interglacial period is the closest interglacial period to the Holocene ice age we are now in.Because of the diversity of record carriers,such as deep-sea sediments,ice cores,loess paleosol,stalagmite records,and rich resolution environmental information,different carriers can also be compared with each other and achieve good results,so it is the best choice for us to understand how the Holocene glacial climate evolved.Loess deposits in China have shown their unique advantages in interpreting the Quaternary paleoclimate environment.However,there are great differences between different regions and different loess profiles in the same region in terms of climate instability and formation mechanism since the last interglacial.Are these differences caused by different climatic information recorded in the loess strata,or by the variation of acquired environment?In order to answer this question,it is necessary to find some new and reliable sections for comparative analysis and verification.Linfen basin is one of the areas with strong neotectonic movement in China.It is located in the south and east margin of Ordos platform,and is also located in the sensitive zone of transition from semi humid area to semi-arid area.The special geographical location determines that the loess paleosol sequence in the region can perceive paleoclimate change sensitively.The loess profile sequence of Dingcun in Linfen basin is complete,which keeps abundant paleoenvironment information,and thus becomes an ideal file for discussing the characteristics of climate instability.This is not only of great theoretical significance to reveal the law of climate change since the last interglacial period,but also lays a foundation for the objective and accurate prediction of future climate evolution in the future.In this paper,based on the Optically Stimulated Luminescence(OSL)dating,through the data processing and analysis of the grain size,magnetic susceptibility,soil chromaticity index and other climate alternative indicators of loess sediments in Linfen basin,we selected them,and finally determined that the magnetic susceptibility,grain size,totle Fe content,soil chromaticity index as the climate and environmental alternative indicators of Dingcun section.On the basis of determining the Environmental Indication Significance of climate proxy index,this paper analyzes and discusses the environmental evolution process and characteristics of Linfen basin since the last interglacial period,and finds that the climate fluctuation events of Linfen basin in the last interglacial period and the last glacial period are consistent with the global climate change,which provides strong evidence for discussing the climate instability characteristics of Linfen basin.The research shows:The last interglacial climate in Linfen basin could be divided into five sub-stages in total:three warm periods(MIS5a?MIS5c?MIS5e)and two cold periods(MIS5b?MIS5d),which had a good correspondence with 5 sub-segments of Marine Isotope stage 5(MIS5).At the same time,the sub-grade climate fluctuated a lot in each sub-segment.In the MIS5a sub-stage,the climate change characteristics indicated by the three climate substitution indexes are not consistent with the two warm and one cold events,which indicates that although the climate in Linfen basin is similar to the global climate change,it also reflects the regional characteristics of climate change;in the MIS5c sub-stage,the climate substitution indexes fluctuate,and the total Fe content(TFe)in the sub-stage of MIS5c shows a"high-low-high"trend which indicates that the climate is unstable at this stage.The median particle diameter in the MIS5b is significantly larger than that in the MIS5d,which means that the paleoclimate of 95-85ka B.P.was colder than 115-105ka B.P..The record is similar to many high-resolution climate records in the northern hemisphere,indicating that this might not only be a local feature,but also a common phenomenon in the northern hemisphere.and the climate of MIS5e in Linfen basin was warm and humid,the alternation of cold and warm was not obvious,and the state was stable.In the last glacial period,the frequency susceptibility and the total Fe content curve of climate substitution index in Dingcun section correspond well compared with the records of Greenland ice core?¹⁸O.Five Heinrich(H)cold events and 19Dansgaard-Oeschger(D-O)cycles are clearly recorded,indicating that the climate of Linfen basin is unstable in the last glacial stage.Compared with the records of Xifeng section,Yili section in Xinjiang and Greenland ice core?¹⁸O,the climate events recorded in this section have a smaller amplitude,which may be because the section is mainly controlled by the East Asian monsoon,and the west wind has less influence on it.It also indicates that the millennium-scale climate events in the last glacial period are consistent with global climate change.