关键词: 螺髻山, 物质平衡线高度, 冰川体积, 冰川纵剖面模型, 古气候

Abstract:

Luoji Mountain is located in the eastern margin of the Qinghai-Tibet Plateau and the central part of the Hengduan Mountains. The well-preserved Quaternary moraines in the Qingshui Valley exhibit great potential for reconstructing paleo-glacier extents and examining climate changes in the region. Three sets of moraines were successively preserved， from the cirques to the mouth of Qingshui Valley. These glacial moraines can be assigned to Penultimate Glaciation （MIS 6）， early stage of Last Glaciation （MIS 4）， and late stage of Last Glaciation （MIS 2）. Guided by the Quaternary moraine features， this study used glacier reconstruction tools to reconstruct paleo-glacier surfaces and glacier equilibrium-line altitude （ELA） for three Quaternary glacial stages in the Qingshui Valley. Researchers previously considered modern terrain instead of ancient ice height when employing the accumulation area ratio （AAR） and area altitude balance ratio （AARB） methods to calculate the ELA， which resulted in an underestimation of the ELAs of ancient glaciers. In this study， the AAR and AARB methods were used to calculate the material balance line height during various periods after ancient glacier restoration to increase the ELA calculation accuracy. For 30 years， from 1990 to 2019， temperature and precipitation data from six weather stations of the National Meteorological Data Center demonstrated that the air temperature decline rate was 0.54 ℃·（100m）^-1. By combining this data with the precipitation-temperature and temperature lapse-rate models， we obtained the climate conditions of different ice ages. The primary findings are as follows： The surface heights of the glaciers were 2 125~3 826 m， 3 380~4 055 m， and 3 765~4 043 m， the glacier areas were 3.44 km²， 2.22 km²， and 1.20 km²， and the glacier volumes were 0.19 km³， 0.12 km³， and 0.07 km³ during Penultimate Glaciation， early stage of Last Glaciation， and late stage of Last Glaciation， respectively. The ELAs of Penultimate Glaciation， early stage of Last Glaciation， and late stage of Last Glaciation were 3 132 m， 3 776 m， and 3 927 m， which were reduced by 1 716 m， 1 071 m， and 920 m， respectively， compared with the modern ELAs. Scale of the glacier was affected by both temperature and precipitation. The large drop （8~12 ℃） in temperature in MIS 6 was the cause of the largest glacier. The precipitation in MIS 4 was about 80% of the current value， but the temperature drop （6~7 ℃） was smaller than Penultimate Glacial Period， so the glacier scale was smaller than that of Penultimate Glacial Period. The precipitation in MIS 2 was only 60%~80% of the present， and the temperature drop （4~8 ℃） was not large， so the glacier scale was the smallest.

Key words: Luoji Mountain, equilibrium-line altitude （ELA）, glacier volume, longitudinal profile model of glacier, paleoclimate