Recent 200 a Climatic Records in the Far East Rongbuk Ice Core, Mt. Qomolangma (Everest), Himalayas
KANG Shi-chang, QIN Da-he, Paul A Mayewski, Cameron P Wake, REN Jia-wen (Laboratory of Ice Core and Cold Regions Environment, CAREERI CAS, Lanzhou Gansu 730000) (Climate Change Research Center.Institute for the Study of Earth. Ocean and Space, University
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.