Glacial And Climatic Changes In Boduizangbu Valley In Baiyu Ice Stage

The last glacial maximum presents the dramatically drop in temperature throughout the world, which enlarges the areas of the ice sheets in two poles, extends the alpine glaciers and reduces the equilibrium line altitude of glaciers. But the dropping of the equilibrium line altitude in different areas is not consistent, and there are two reasons for it. On the one hand, the dropping extents in temperature are different;on the other, the equilibrium line altitude is the result of temperature and precipitation, and the influence of topography in the glacial developing area. After the last glacial maximum, the global temperature increases, resulting in the retreats of alpine glaciers, which shaped inimitable glacial landscapes. These various and majestic landforms are of natural landscape, and in different areas and positions, the glacial landforms are different. The study on the style, scale and area of moraines, which are formed by glacial erosion and accumulation in the last glacial maximum, is important for studying the quality, process and erosive accumulation of glaciers in the last glacial maximum. According to the relationship between variations of modern glaciers and climatic conditions, the climatic conditions in the last glacial maximum were reconstructed, in order to understand the effect of temperature, precipitation and topography on glaciers, and the influence of the south Asia monsoon on glaciers, especially on variations of the equilibrium line altitude, to infer the regional climatic change in the future, its contributions to the global climatic change, and the effect of global climatic change on regional climatic change.The southeast Nyanqingtanggula Mountains in the Tibetan plateau develop modern glaciers in large scale, and the last glacial maximum remains large-scale moraines, typically that in the valley of Boduizangbo in Bomi, and that in modern glaciers in the drainage area. Lateral and terminal moraines are very prominent sediments, and they can be used to completely reconstruct the scale, size, length and thickness of the typical glaciers in the valley during the last glacial maximum.The 11 samples of ESR were collected in the Baiyugou valley and in theneighboring fluvioglacial terrace, the age of the sample BYG -1(ESR) at the first moraine is ll.l±1.6ka BP;the age of sample XM -1 at the hummocky moraine is 12.3±1.8ka BP. So the hummocky moraine represented by the sample suggested it may be formed in Boiling event or Allerod warming period in the lateglacial.The 614Csamples were collected in the 2-layer palaeo-soils in the fluvioglacial sediment of Baiyugou valley and neighboring Buduizangbu valley. The two sample ages in the lower layer were 7190±120a BP and 5230±120a BP;the 4 sample ages in the upper layer were 3755±125aBP, 2670±130aBP, 3450±70 a BPand 3335±85 a BP. The sample ages suggest southeast Tibetan Plateau had developed palaeo-soil during the early mid-Holocene(7.2 - 5.5ka) and during the late mid-Holocene, representing warm and moist climate, which is mutually consistent with the climate of the Hebei plain.Late Quaternary glacier fluctuations in the Boduizangbu valley were reconstructed using relative and absolute dating techniques. Our results indicate that younger moraine complexes were left by YD event (cal 11 ka BP) and Lateglacial (ca 13 cal. ka BP) ice advances. Older Late Quaternary glacier advances occurred during Marine Oxygen Isotope Stages (MIS) 6. No relics of Middle or Early Pleistocene glaciations could be found. During MIS6, glaciers advanced down to an altitude of at least 2600m a.s.l., corresponding to an ELA depression of approximately 1300 m. At about 2700m a.s.l., the YD glacier reached almost the thickness of the former MIS2 glacier and retreated some time before 16 cal. ka BP. The Lateglacial glacier advanced again several times to altitudes between 2700 and 2800m a.s.l.Based on the map of 1:100,000, the satellite images in 1987 and 1999, and the meteorologic data gathered from 34 weather stations in research areas, a detailed topography analysis and comparison was made to explore the data's spatial feature. According to the spatial analysis of GIS and the quantitative analysis of the remote sensing, three typical glaciers were chosen, in order to respectively calculate the terrain parameters, including length, area, height and gradient and so on. The characteristics of the vertical sections and cross-sections of Zhuxigou and Baiyugou were discussed in detail, and the feature was analyzed. At the end, the effect of thebedrock and its topography on the glaciers was discussed.ELA was calculated through the weighted average and three different methods. The height of ELA of Baiyu ice age can be got, respectively 4004m asl, 3827m asl and 3882m asl, and each of them descend down 602 m, 380m and 372m, compared with that of modern times. By analyzing the statistics of temperature and precipitation in the nine weather stations around the research area, a distributed model of temperature and precipitation based on DEM was established, and the results show the gradient of summer average temperature in the southeast Tibet is lower than the vertical gradient of annual average temperature. According to the relationship between ELA and temperature (summer temperature) & precipitation (solid precipitation), the variation of climatic factors (temperature and precipitation) in the research area in the last glacial maximum were discussed.