Late Quaternary Glacial Advances And Related Climate Conditions In The Siguniang Shan,Eastern Margin Of The Tibetan Plateau

Many mountains in the Tibetan Plateau have established chronological sequences of Quaternary glacier evolution,but most of them are dominated by the glacial-interglacial cycles?orbital scale?.Recently,the response of glaciers to sub-orbital scale climate change has also been found in some mountain ranges,but these research is not thorough enough.Therefore,there is a lack of systematic understanding of the pattern of glaciers evolution on sub-orbital scale and its climate driving mechanism.In this work,we selected the Siguniang Shan,an extremely high mountain with oceanic glaciers on the eastern edge of the Tibetan Plateau,as the research area,because monsoon warm glaciers?marine glaciers?are more sensitive to climate change and have stronger erosion capabilities,these shorter time scale glacial fluctuations are most likely to be recorded.Therefore,we conduct research work on the evolution of late Quaternary glaciers in the Siguniang Shan with a view to improving the understanding of the above issues.In addition,the Gongga Shan range,which is also the highest mountain in the eastern margin,has established a relatively complete chronological sequence of paleo-glacier evolution.Since the last glacial period,the glaciers in this range have also responded many times to sub-orbital climatic events.Our research focuses on the evolution of paleo-glacier of the Siguniang Shan in the last glacial,to conduct the chronology and the simulation study of paleo-glacier.Therefore,combined with previous studies on the Gongga Shan,this work not only helps to establish a more complete scale of the age and scope of paleo-glaciation in the extremely high mountains of the eastern margin of the Tibetan Plateau,but also may reveal the response patterns of glaciers to sub-orbital scale climate change events and its climate driving mechanism.Based on the above goals and ideas,this work first carried out ¹⁰Be exposure dating?32 samples?for glacier deposits in Changpinggou and its downstream valleys which is the most complete glacier deposition sequence in Siguniangshan.Then combined the chronological sequences of previous studies in the Gongga Shan,we established the age scale of the paleo-glacier evolution in the highest mountains of the eastern margin of the Tibetan Plateau;Secondly,to analyze the similarities and differences of various regions and their possible influencing factors through the comparison of glacial evolution patterns on a large regional scale;Finally,Finally,this work reconstructed the ice volume of each stage for ice inflow,ELA and corresponding temperature and precipitation combination through the 2-D glacier flow model,and then discussed the climate driving mechanism of the evolution of paleo-glaciers in the eastern margin of the Tibetan Plateau.We initially obtained the following main conclusions:1.The exposure ages of ¹⁰Be for Zhongliangzi stage,Dayingpan stage and Rilongguan stage in Siguniang Shan are 28.69±2.73³0.65±6.89 ka?n=12?,20.17±1.91²2.78±2.15?n=8?and 15.81±1.51¹7.88±1.68 ka?n=11?,roughly corresponding to the three sub-orbital scale cooling events?H3,H2 and H1 events?of the last glacial period;combining with the Quaternary glacial age sequences of the Gongga Shan,the highest mountains on the eastern margin of the Tibetan Plateau have experienced at least 8 large-scale ice advances including MIS6,mid-MIS3,H3,H2,H1,Early Holocene,Neo-glacial,and Little-glacial.The paleo-glaciers in this range can not only record information of climate change on the orbital scale,but also respond sensitively to climate fluctuations on the sub-orbital scale.2.Based on the existing precipitation data,it is respectively assumed that the precipitation of H3,H2 and H1 in the last glacial period is 40%⁸0%,40%⁸0%and 50%⁸0%of that in modern times.The corresponding areas of the reconstructed glaciers in each period were 310.4³10.9 km²,299.2³00.4 km² and 153.4¹55.4km² respectively.The ice volume was 36.3⁴3.9 km³,33.2⁴0.2 km³ and 20.6²3.8km³ respectively.The ELA is reduced by 1322¹172?1247?m,1256¹121?1189?m and 1201¹107?1154?m compared to modern?5105 m?.The temperature should be lower than modern by 10.0⁸.5°C,9.5⁸.1°C and 9.0⁸.0°C respectively.3.In the highest mountains on the eastern margin of the Tibetan Plateau,the second-level glacial advance during the glacial period may be driven by sub-orbital-scale cooling events,reflecting the temperature signals of high latitudes in the northern hemisphere;In the inter-glacial or inter-glacial stage,the second-level large-scale glacial advances require the coordination of sub-orbital-scale cold events and increased precipitation,which may reflect the combined effects of high latitude temperatures and low-latitude summer monsoons in the northern hemisphere.