【摘要】 分析了从南亚经青藏高原到毗邻的我国西北地区一个经向剖面上降水中稳定同位素成分的时空分布以及与温度、降水量、水汽来源的关系 .在青藏高原南部和南亚 ,温度效应均不存在 .在所统计的站点中 ,大约一半的取样站具有降水量效应 ,但降水中稳定同位素比率的季节变化并不与降水量强度的变化相一致 .在季节变化中 ,δ18O的最大值往往出现在雨季到来之前的春季 ,最小值则出现在雨季后期或雨季结束的秋季 .在青藏高原中、北部和毗邻的我国西北地区 ,各取样站均具有显著的温度效应 ,且降水中δ18O的季节变化与温度的季节变化几乎一致 .说明在这些地区 ,温度是制约降水中稳定同位素变化的主要影响因子 .由于来自源区水汽的直接凝结 ,南亚地区降水中平均稳定同位素成分相对较重 .稳定同位素比率的季节差异较小 ;从青藏高原南坡的坚景到唐古拉山 ,由于翻越喜马拉雅山时水汽受强烈的洗涤作用 ,降水中稳定同位素比率急剧减小 ,达经向分布中δ18O的最低值段 ;从 31°N到青藏高原北部 ,降水中稳定同位素比率随纬度而增大 ,并最终过渡到与我国西北地区降水中稳定同位素比率的变化型相类似 .更多还原

【Abstract】 The temporal and spatial variations of stable isotopic compositions in precipitation and their relationship with temperature, precipitation and vapor sources are analyzed in a meridianal section of the Tibetan Plateau and its adjacent regions. There is no temperature effect in the southern Tibetan Plateau and South Asia. Amount effect has been observed at New Delhi, Katmandu, Kyangjin and Lhasa that account for about a half of the statistical stations. However, the seasonal variations of stable isotopic compositions in precipitation at those stations are inconsistent with that of precipitation intensity: the maximum δ 18 O in precipitation usually appears in spring before the rainy season, and the minimum δ 18 O in precipitation is in fall during the late rainy season or after the rainy season. This distribution shows that the variations of stable isotopic compositions in precipitation are not mainly controlled by precipitation intensity in the southern Tibetan Plateau and South Asia. There is notable temperature effect in the middle northern Tibetan Plateau and its adjacent Northwest China. It has been observed that the seasonal variations of δ 18 O in precipitation are almost consistent with those of air temperature in these regions, which shows that temperature is a main factor controlling the stable isotopic variations in precipitation. The relationship between the weighted mean δ 18 O and the mean temperature on the Tibetan Plateau and its adjacent regions is not distinctly different from the global scale pattern. Comparatively speaking, during the cold season, there is a closer correlation between the weighted mean δ 18 O and the mean temperature on the Tibetan Plateau and its adjacent regions, with a nonlinear correlation coefficient reaching 0.9414. This probably arises because all of Asia is under the control of the strong cold high pressure over Mongolia during the winter season. The situation during the warm season is different. Although the general trend of the weighted mean δ 18 O with the mean temperature has not been changed, the spatial variation clearly displays that the weighted mean δ 18 O for the stations from Kyangjin on the southern slope of the Himalayas to the Tanggula Mountains in the middle Tibetan Plateau are all lower than the typical ones of the globe for the same temperature. As for the other stations on the middle and northern Tibetan Plateau in the north of the Tanggula Mountains and Northwest China, their weighted mean δ 18 O , all greater than -10.0‰ , are distributed around the global regression line. Because vapor is directly originated from low latitude oceans, the relative heavy δ 18 O with small variation characterizes the rainfall in South Asia. A sharp depletion of stable isotopic compositions in precipitation takes place from Kyangjin on the southern slop of the Himalayas to the Tanggula Mountains in the middle Plateau. δ 18 O reaches its minimum due to very strong rainout of the vapor from oceans as the vapor rises over the Himalayas. From the Tanggula Mountains to the northern Tibetan Plateau, δ 18 O in precipitation increases with increasing latitude. Isotopes in the northern Plateau transfer into the Northwest China with little disruption.更多还原