Modern stalagmite oxygen isotopic composition and its implications of climatic change from a high-elevation cave in the eastern Qinghai-Tibet Plateau over the past 50 years

摘要

An oxygen isotope record of a stalagmite from Huanglong Cave in the eastern Qinghai-Tibet Plateau dated with ~(230)Th and ~(210)Pb methods provides variations of the Asian monsoon with an average resolution of 1 year over the past 50 years. This studyshows that the delta~(18)O of dripwater in the cave represents the annual mean delta~(18)O of local meteoric precipitation and the stalagmites were deposited in isotopic equilibrium. A comparison of the stalagmite delta~(18)O record with instrumentallymeteorological data indicates that shifts of the delta~(18)O are largely controlled by the amount effect of meteoric precipitation conveyed through the southwest monsoon (the Indian monsoon) and less affected by temperature. Therefore, the variations ofdelta~(18)O record reflect the changes in monsoon precipitation on inter-annual time scales under the influence of the southwest monsoon. Like many other stalagmite delta~(18)O records in the Asian monsoon regions, the delta~(18)O record of the stalagmite from Huanglong Cave also reveals a gradually enriched trend during the past 50 years, i.e. relatively enriched in ~(18)O. This trend may indicate the decline of the Asian monsoon intensity which is consistent with the decrease of monsoon indices. The weakening of the modern Asian monsoon well matched with the temperature changes in stratosphere, which may illustrate that the weakening of the monsoon mainly results from the lowering of solar radiation.