近200a来珠穆朗玛峰北坡远东绒布冰芯气候记录

Recent 200 a Climatic Records in the Far East Rongbuk Ice Core, Mt. Qomolangma (Everest), Himalayas

１９９７年 ５月中美联合珠穆朗玛峰地区绒布冰川考察期间，在远东绒布冰川海拔 ６ ５００ ｍ的北 支冰流粒雪盆内钻取到一支４１ｍ长冰芯．通过数年层法并根据β活化度的参照年（１９５４年和 １９６３ 年），对远东绒布冰芯实施定年，冰芯底部为 １８１４年，冰芯年平均净积累量为 ２２４ ｍｍ（冰当 量）．根据远东绒布冰芯 （δ１８Ｏ的变化，重建了珠穆朗玛峰北坡地区近 ２００ ａ气候变化，发现有 ５次冷 期和５次暖期，且总趋势为变暖，这与本世纪北半球气候变暖的趋势相一致．远东绒布冰芯气候记 录同古里雅冰芯比较，两者的冷暖波动较为一致，说明青藏高原西北部和南部地区的气候变化具有 共性．但是，远东绒布冰芯中δ１８Ｏ的变化在短时间尺度上与降水量变化存在某些反相关性，这种关 系并未影响到δ１８Ｏ反映气温的长期变化趋势．

During the Sino-American Expedition to Mount Qomolangma in May 1997, an ice core, 41 m in length, was recovered at the elevation of 6 500 m from the northern firn basin of the Far East Rongbuk Glacier in the Mount Qomolangma. The ice core was dated down to 1814 by means of counting δ18O and major ion concentration peaks and referring β activity years (1954 and 1963). The average annual accumulation rate is calculated to be 224 mm/ a (ice equivalent). This paper focuses on the variation of δ18O in the ice core to understand the climate change in the area of Mount Qomolangma. There are five cold periods and five warm periods recognized by the ice core records. In the recent decades, the cold intensity in the cold periods was weaker and weaker, and the warm intensity in the warm periods was stronger and stronger. This general warming tendency of climate change is agree with the temperature change tendency in the Northern Hemisphere. Al- so the climatic records in the Far East Rongbuk ice core has good agreement with that in the Guliya ice core in West Kunlun Mountains. Especially in the 19th century, the fluctuation of δ18O recorded both in the Far East Rongbuk ice core and the Guliya ice core was identical, and a cold period in the 1930s was obvious in both records. This indicates that the climate change was consistent in the northwestern and southern Tibetan Plateau, though the local geophysical conditions of the two sites are difference. The seasonal δ18O variations reflects the amount effect' (e.g. lower δ18O occurs in summer monsoon season). The δ18O variations has a negative correlation with precipitation also can be extended to the scale from several years to decade, which is verified by a comparison between the monsoon precipitation in northwestern India and δ18O records in the Far East Rongbuk ice core. In recent 40 a, there are also some reverse tendencies between δ18O and annual precipitation from Xigaze Meteorological Station, as well as some similar trends between δ18O and annual temperature. These may indicate that δ18O records are influenced by both of precipitation and temperature on short time scale (several years). When the change of precipitation is larger,' amount effect' should be the dominant factor. But in a long time scale (e.g. several decades to hundreds), the dependence of δ18O on temperature does not change owing to the relation between δ18O and precipitation mentioned above. It should be also noted that, on the background of warming in the Plateau, the δ18O value from Far East Rongbuk ice core has been decreasing since late 1980s. In fact controls on the isotopic fractionation of moisture deposited on the southern margin of the Plateau have changed over the last few decades. The increases in temperature over the last few decades have led atmospheric circulation to change, resulting in a decrease in moisture flux to the Plateau. Thus, since the 1980s, influence factors of δ18O have been not simply attributed to precipitation and temperature but more complicated, and should be a combination of many factors and processes. This needs further study.