Research On Millennium-scale Climate Events Of The Last Glacial Age Recorded By Loess Sedimentary Records In The Linfen Basin

Global change has long been a hot topic of attention and research in the field of geography.Millennium-scale climate abrupt events,as the most prominent feature of the last glacial climate,are also the focus of Quaternary paleoclimate research.Ice cores,deep-sea sediments and loess,as the three pillars reflecting global climate change,all reveal the unstable characteristics of the rapid climate change during the last glacial period.Although such climate events have been recorded on a global scale,different regions and different profiles in the same region show differences in the reflection of the events,so that there is no accurate conclusion on the causes of climate abrupt events,so it is very important to find a large number of high-precision geological records in more areas for research.Loess is a good information carrier for paleoclimate research,and records rich climate information.Since the last glacial period,the loess on the Loess Plateau has the following advantages:fast deposition rate,complete and continuous soil preservation,and high soil resolution.It is suitable for high-precision dating to obtain more accurate paleoclimate information.The Linfen Basin is located in the transition zone between semi-humid and semi-arid regions,and its location is sensitive and its response to climate change is relatively sensitive,which enables the loess-paleosol sequence in this region to accurately reflect the changing characteristics of paleoclimate.The soil sedimentary sequence of the Dingcun section is relatively complete,recording rich paleoclimate and paleoenvironmental information,so it is very beneficial to the study of climate instability.In this paper,on the basis of optical luminescence dating,the chronological sequence of the region is reconstructed by using the grain-size age model,and the climatic alternative indicators of the loess sediments in the Linfen Basin are tested to determine the climate evolution characteristics of the last glacial stage,revealing the millennium of the last glacial period.The performance and regional characteristics of the scale climate abrupt events in the Linfen Basin,the formation and driving mechanism of the millennium-scale climate abrupt events were preliminarily discussed,and the Greenland ice core,the western Loess Plateau and the typical profiles under the control of the westerly wind were compared and analyzed,and the mid-latitude region of East Asia was found.The relationship between the climate fluctuations since the last glacial period and the North Atlantic region is of great significance for understanding the climate change of the entire Loess Plateau.The main conclusions are as follows:The paleoclimate evolution stages since the last glacial period in the Linfen Basin can be divided into: the depth of 420-190 cm is the early glacial stage of the last glacial period(about73.79-58.41 ka BP,MIS4 stage);the depth of 190-60 cm is the last glacial period Ice stage(about58.41-28 ka BP,MIS3 stage);the depth between 60 and 0 cm is the last glacial stage or the last glacial maximum period(about 28-20 ka BP,MIS2 stage).The high-resolution loess records in the Linfen Basin showed low-amplitude and high-frequency changes throughout the last glacial period.The results of evolution spectrum analysis show that the median particle size shows main periods of 1400 a,1100 a and 690 a,and the frequency magnetic susceptibility shows main periods of 1490 a and 630 a;the evolution of winter and summer monsoons is complex and changeable.The wavelet analysis results show that although the quasi-periods of 1470 a and 1490 a exist,there are obvious differences in the signal strength in different time periods.Therefore,the cause of the millennium-scale climate change during the last glacial period in the Linfen Basin may be more influenced by solar radiation.The Linfen Basin climate proxy indicators recorded 5 Heinrich beats and 19 D-O cycles,and the occurrence times of the 5 H events were 23.9 ka B.P.,31.3 ka B.P.,37.5 ka B.P.,47.6 ka B.P.,and 61.4 ka B.P.,respectively.Among them,H2 and H6 events have the largest changes in amplitude and the most obvious signal changes,followed by H5,and H3 and H4 are the smallest.The increase in temperature during MIS3 and the uniqueness of the regional climate may have weakened the records of these two cold events.In addition,there are slight differences in the appearance time of the same climate event on different indicator curves,indicating that the reflection of climate events by alternative climate indicators is asynchronous in time.The millennium-scale climate events recorded from the Dingcun profile in the Linfen Basin are in good agreement with the corresponding records from the Greenland ice core,indicating that there are climate event signals in the high-latitude polar regions in the loess in the mid-latitude regions of the northern hemisphere.And compared with the records of the Lijiayuan section of the Loess Plateau,the Zeketai section of Xinjiang and the Tajikistan section,there is a good correspondence.From west to east,the closer to the active summer monsoon region,the smaller the signal intensity and the weaker the performance,indicating that the millennial-scale climate fluctuations of the last glacial period in the East Asian monsoon region are affected by the combined action of the westerly wind and the East Asian summer monsoon.