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Chapter 06
Climate and Study of Glaciers
Generally, the glaciers in the Gongga Shan during the Neoglacial period were 3-9 km longer than at present, whereas the LIA glaciers were between several hundreds of meters to 3 km longer than the present ones (Su et al., 2002). Thus, the glacier advances during the LIA did not exceed those of the Neoglacial period in the Gongga Shan. Evidence of glacier advances from the eastern Nyainqentanglha Range (Wang and Fan, 1987; Jiao et al., 2005) and from the eastern Himalayan Mountains (Zhang, 1988) repeats this general pattern.
The equilibrium line altitude (ELA) variation is a good indicator of climate change determining glacier fluctuations in the case of monsoonal temperate glaciers. According to ELA variations, one can estimate temperature variations during the different periods of glacier advance. Benn and Lehmkuhl (2000) reviewed several methods commonly used for ELA reconstruction of glaciers in high-mountain environments influenced by avalanches, debris cover and topographic effects. They suggested that the toe-to-summit method of Louis (1955) can yield good results where mass-balance data are unavailable. Taking the Zepu Glacier as an example, we estimate temperature fluctuations in different periods of glacier advance during the last 2000 years. The altitudes of the terminal moraines at about 200-600 AD, 800-1150 AD, the earlier stage 1400-1650 AD of the LIA, and the 19th century are 3100 m, 3200 m, 3300 m, and 3400 m, respectively. The present glacier terminus altitude is 3420 m. The calculated corresponding ELA depressions are 160 m, 110 m, 60 m, and 10 m, respectively.
Zhang (1988) obtained the ELA depressions of 120 m and 60 m for the Neoglacial and LIA periods for the Zelongnong Glacier in the eastern Himalayan Mountains when an accumulation area ratio (AAR) value of 0.6 was chosen. At the Yanzigou Glacier in the Gongga Shan, Smiraglia (1997) estimated that the ELA depression during the phase of maximum expansion during the last 4000 years was 180m. In this case, AAR value of 0.67 was applied. In addition, Li and Su (1996) reported that the ELA depressions in Hailuogou Glacier during the Neoglacial and LIA periods were 150 m and 50 m respectively. These results are in agreement with our estimates, showing that the rise and decrease of the Zepu Glacier ELAS can be regarded as being representative for the ELA fluctuations on the southeastern Tibetan Plateau.
According to Shi et al. (1992), Kadota and Ageta (1992). Ageta and Kadota (1992). ELA variations in monsoonal temperate glacier areas are much more sensitive to summer mean temperature than to total annual precipitation. A slight temperature rise can result in a largescale glacier retreat, and vise versa, especially for the glaciers with a summer mean temperature >2 °C at the ELA altitude (Shi, 2002). Li et al. (1986) reported that summer mean temperature at the ELA of Zepu Glacier is about 4 °C. If this decrease in altitude is attributed solely to a temperature reduction and if a thermal gradient of 0.65 °C/100 m is assumed, temperature on the southeastern Tibetan Plateau would have been lower than at present (1989 AD) by 1.0 °C, 0.7 °C, 0.4 °C and 0.1 °C during the periods of 200-600 AD, 800-1150 AD, 1400-1650 AD. and during the 19th century, respectively.
4. Discussion and conclusions
In this paper, we examine the relationship between glacier variations and climatic change in eastern High Asian mountain regions. Here we adopt the temperature reconstruction covering the last two millennia for the Tibetan Plateau, which was derived from multi-proxy data such
Late Holocene monsoonal temperate glacier Fluctuations...
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