A Study Of Glacier Changes And Surface Dust On Legnlongling Glacier In The Qilian Mountains

Glacier is an important component of the climate system, and is considered indicator of climate changes. Glacier variation is well focused now in relation to global climate change and water cycle. Factors causing accumulation-ablation process are usually thought to be physical conditions around the glaciers, such as precipitation and air temperature. Melting usually occurred on the glacier surface, and is a main process during the glacier ablation period. Evaporation is not important, because ice vaporizing need much more energy than ice melting. According to the observations of glacier surface energy balance, the net solar radiation flux is the dominant energy source for the glacier ablation; followed by the sensible heat flux and the latent heat flux usually contribute negatively to the budget.Study of glacier changes usually focused on the surface energy balance and mass balance. However, recent studies showed that the surface dust of the glacier may play an important role in the glacier change. Surface dust cover can decrease effectively the surface albedo of the glacier, because of its darkly cooler. The reductions of surface albedo increase the solar radiation absorbed by the glacier surface and results more melting of the glacier. Therefore, studies of the composition, quantity, distribution and migration of the surface dust are important to research of glacier changes.In this paper, Lenglongling that located east part of the Qilian Mountains was selected as sample region to investigate glacier by using Landsat ETM+ during 1999-2002. The glacier changes have been investigated comparing digitized glacier outlines from the first Chinese Glacier Inventory (CGI) during 1960s-1970s. For study of the glacier surface dust, samples were collected from the ablation zone on the Gangshika Glacier. And then, particle size and amount of organic matter of the dust samples were analyzed in the Key Laboratory of Western China's Environmental Systems. The work is summarized as followings:1. Surface dust usually consists of mineral particles and organic matter. The surface dust had a characteristic granular form. Many micro-plants have glutinous materials around them, these micro-plants might get together with mineral particles and plant fragments etc. These mud-like granules were cohesive and not easy to break.2. The mineral particles in the dust usually originate from basal till and/or wind-blown sands. The particle size analysis of the dust samples showed that the main component of mineral particles is the slit, followed by the sand and then the clay.3. The amount of organic matter in the dust is different with the elevation of different sampling sites, because of the changes of living condition of the micro-organisms in the dust. This suggested that the amount of organic matter in the dust was closely related to biological productivity.4. The spectral albedo generally decreased as the wavelength increased (550nm～1000nm). The surface albedo ranged from 0.12 to 0.49 in the ice area. In the snow area, the albedo were generally higher than those in the ice area, and ranged from 0.67～0.72.5. The investigation of glacier area in the Lenglongling indicated that the glacier area was 73.17km², and decreased by 29.85km² from the first CGI to 2002, accounted for -28.97% of the glacier area and 0.77km²a^-1, accounted for 0.74%a^-1.6. According to the glacier surface energy balance equation during ablation period, the change of energy absorbed by glacier surface that causing by decreasing surface albedo by 0.1 equaled to the change causing by increasing air temperature by 2.7K. This suggested that the albedo of glacier surface played a more important role than air temperature to the glacier change. The dust covered on the glacier surface mainly decreased the surface albedo. So, the reduction of albedo by surface dust was the main factor accelerated glaciers retreating in the context of global warming.