亚洲降水中δ18O沿不同水汽输送路径的变化

利用IAEA/WMO全球监测网和青藏高原的监测站,建立了由赤道地区经我国西南水汽通道至长江中下游的南方水汽输送路径、沿西风带自我国西部经华北至日本的北方水汽输送路径以及自南亚穿喜马拉雅山到我国青藏高原的水汽输送路径的取样剖面,比较了三条水汽路径在不同季节降水中啄18O的变化及其与温度、降水量的关系。沿南方水汽路径,低纬度地区取样站降水中平均啄18O的季节差异较小。沿北方水汽路径,郑州以西取样站平均啄18O的季节差均大于郑州以东的取样站。随着经度的增加,降水中平均啄18O的季节差减小。沿高原水汽路径,印度次大陆南部降水中的啄18O相对较高,随着纬度的增加,降水中啄18O逐渐减小。在翻越喜马拉雅山后,由于强烈的洗涤作用,降水中啄18O急剧下降。

Variations of δ18O in Precipitation along Vapor Transport Paths over Asia

Three sampling cross-sections along the south path starting from the tropics through the vapor passage in the Yunnan-Guizhou Plateau to the middle and lower reaches of the Yangtze River, the north path from west China, via north China, to Japan under the westerlies and the plateau path from South Asia over the Himalayas to the northern Tibetan Plateau, are set up, based on the IAEA/WMO global survey network and sampling sites on the Tibetan Plateau. The variations, and the relationship with precipitation and temperature, of the δ¹⁸O in precipitation along the three cross-sections are analyzed and compared. Along the south path, the seasonal differences of mean δ¹⁸O in precipitation are small at the stations located in tropics, but increase markedly from Bangkok towards the north, with the δ¹⁸O in the rainy season smaller than that in the dry season. Along the north path, the seasonal differences of the mean δ¹⁸O in precipitation for the stations in the west of Zhengzhou are all greater than that in the east of Zhengzhou. Along the plateau path, the mean δ¹⁸O values in precipitation in the rainy season are correspondingly high in the southern parts of the India Subcontinent, and then decrease gradually with latitude. A sharp depletion of the stable isotopic compositions in precipitation takes place due to the very strong rainout of the stable isotopic compositions in vapor in the process of the lifting on the southern slope of the Himalayas.