Isotopic measurements of precipitation on central Asian glaciers (southeastern Tibet, northern Himalayas, central Tien Shan)

The glacial regions of central Asia considered in our study are influenced by tropical monsoons and western extratropical cyclones. Isotopic delta(18)O and delta D data were obtained over 3 years in three climatic regions: Gongga massif of southeastern Tibet (windward slope of summer monsoon), Xixibangma massif on the northern slope of the Himalayas (leeward of summer monsoon), and the massifs of Pobeda-Khan Tengry in the central Tien Shan (exposed to western airstreams). The survey reported here provides information from atmospheric precipitation, snow pits and a 23 m ice core. The significant differences of oxygen isotopic ratios (from -25.1 per mil to -9.5 per mil) indicate that the Indian and Pacific Oceans as well as the Atlantic Ocean ate sources of moisture on the northern slope of the Himalayas and southeastern Tibet. Sharply changing isotopic ratios in precipitation corresponded to changing wind direction and were associated with different sources of air masses on the northern slope of the Himalayas and southeastern Tibet. Steady isotopic ratios in atmospheric precipitation and the absence of changing delta(18)O composition in a 23 m ice core suggest only one source of moisture in central Tien Shan. The relatively heavier oxygen isotopic ratios in atmospheric precipitation and ice core indicate the moisture from which the precipitation was derived originated over the Caspian or Mediterranean seas. Within the Eurasian continent, air masses developed over the Atlantic Ocean advance farther than those from the Pacific and Indian Oceans.