Quantitative Reconstruction Of Paleoclimate In The Middle Section Of The Taniantaweng Mountains

Since the Quaternary,glaciers have expanded and retreated due to the alternation of warm and cold climates,leaving abundant glacial remains in glacial areas.These remains are important evidence for understanding the environmental evolution of Quaternary glaciers.The equilibriun-line altitude?ELA?is the zero balance of glacier accumulation and ablation.Since the fluctuations in ELA are mainly driven by climate,the hight difference between past and present ELA is considered as a reliable indicator of climate change.The middle section of the Taniantaweng Mountains is located between the Nujiang River and Lantsang River in the western region of the Hengduan Mountains,which is the transition zone from Yunnan-Guizhou Plateau to southeastern Tibet.The study area belongs to the maritime glaciation area,which mainly develops hanging glacier and cirque glacier.Field investigations were carried out on the glacial relics of Qinggulong,Juequ and Ruqu in the middle section of the Taniantaweng Mountains,focusing on the morphological features and characteristics of the Quaternary glaciers.Using the profile,the macroscopic and microscopic sedimentary features of the hail are studied.By examining the combination and distribution of glacial erosion and accumulation geomorphology,the scope of action of each stage of glaciers is determined.By using Cosmogenic ¹⁰Be and ESR dating methods,the moraines in Qinggulong and Juequ were chronologized and the glacial sequence in the middle section of the Taniantaweng Mountains was established.Based on the changes in ELA,the model was used to reconstruct the paleoclimate during different glacial periods.The main conclusions are as follows:?1?The analysis of glacial geomorphological characteristics in the middle section of the Taniantaweng Mountains shows that there have been four glacial advance since the late Quaternary.In combination with ¹⁰Be exposure age and ESR results,we can find that the middle section of Taniantaweng Mountains has preserved four stages of glaciations:MIS 690.73±8.71ka),MIS3?30.99±2.97ka?,LGM?15.43±1.46ka²1.26±2.04 ka?and eH?8.18±0.78ka⁸.54±0.82ka?.?2?The height of present ELA in the middle section of the Taniantaweng Mountains is5385m.According to the geomorphological characteristics of Qinggulong and Juequ valley,the CF,THAR,AAR and AABR method were used to reconstruct the ELA of MIS 6,MIS3,LGM and eH stages.The results were:4750m,4867m,5183m,5309m.The paleoclimate of MIS 6,MIS 3,LGM and eH in the study area was restored by using P-T model and LR model combined with existing climate records such as sporopollen,ice core and stalagmite.Considering the annual precipitation ratio of the middle section of the Taniantaweng Mountains during MIS 6,MIS 3,LGM and eH were 60⁸0%,50⁸0%,10⁵0%and 60¹00%,the drop of temperature were:9.72¹1.34°C,9.16¹0.61°C,7.68¹0.56°C and 5.62.⁷.71°C.?3?The large-scale glacial advance in MIS 6 is the result of the precipitation increase caused by the enhancement of monsoon action and combined with the lower temperature.The glacial advance event in MIS 3 of the last glacial period corresponds to the global millennium scale cold event H3.This glacial advance is mainly driven by the combination of lower temperature and more precipitation.The glacial advance in the LGM period corresponds to the Heinrich 2 event.During this period,the climate was cold and dry,and precipitation was scarce.The main factor affecting iceglacial advance during the LGM period is the temperature drop.The glacial advance event during the eH period was affected by the 8.2 ka cooling event in the early Holocene North Atlantic region.Low temperatures and abundant precipitation are the main drivers of this glacial advance.