青藏高原水汽输送与冰芯中稳定同位素记录*

降水中稳定同位素作为水中的组成成分,与水汽来源的变化存在直接的关系。根据在青藏高原降水中稳定同位素的研究,青藏高原南北降水中δ¹⁸ O和过量氘(d)都存在着显著的空间变化,这种空间变化与西南季风夏季向北推进的位置有关。在时间变化上,青藏高原不同地区降水中δ¹⁸ O和d的季节变化特征也与水汽来源的季节变化有关,而且这种季节变化主要受控于西南季风水汽与西风带输送水汽之间的相互作用,在中国最北端的阿尔泰山区还受到极地气团的影响。由于不同的大气环流造成的水汽来源的差异,青藏高原冰芯中稳定同位素变化也存在空间差异。北部地区冰芯中稳定同位素的年际变化与当地气象站记录显示良好的对应关系,而南部冰芯中稳定同位素的变化与当地气象站降水量在年际变化上显示反相关关系。

STABLE ISOTOPES OF PRECIPITATION AND ICE CORE ON THE TIBETAN PLATEAU AND MOISTURE TRANSPORTS

Stable isotopes of precipitation are directly related to the moisture sources. This effect has potential impact on the stable isotopic record from ice cores on the Tibetan Plateau. A net work of stable isotopes of precipitation has been set up in West China in recent years. The spatial and seasonal variations of both δ¹⁸ O and d-excess of precipitation in different parts of West China are monitored to calcify the impact of moisture sources related to the atmospheric circulation.The result shows that there is a large spatial difference on δ¹⁸ O and d-excess of precipitation, which is largely caused by the northward intrusion of southeast monsoon in summer to the Tanggula Mts. For the seasonal variations, the summer lower δ¹⁸ O and d-excess and winter high δ¹⁸ O and d-excess of precipitation in the southern Tibetan Plateau reflect the alternation of summer southwest monsoon moisture transport and winter westerly moisture transport. In the northern plateau, the higher δ¹⁸ O in summer and the lower δ¹⁸ O in winter are due to the fairly monotone moisture sources from the West; while the seasonal variations of d-excess in this region are resulted from the large contract of humidity conditions over the Atlantic Ocean in summer and in winter. In Altay, the north most of West China, polar air mass also affects the regional precipitation, which can also be found from the seasonal isotopic variations. The difference of moisture transports, driven by different atmospheric circulations, also affects the ice core isotopic record on the Tibetan Plateau. In the northern Tibetan Plateau, there is a consistent variation between ice core δ¹⁸ O record and local meteorological air temperature record; while in the southern Tibetan Plateau, δ¹⁸ O in ice core shows an apparent negative relation with precipitation amount in both seasonal and annual time scale.