古里雅冰芯氧同位素地层学

OXYGEN ISOTOPE STRATIGRAPHY OF THE GULIYA ICE CORE

在冰芯研究中，氧同位素比率不仅是气温的一种代用指标，而且其变化又是冰芯年层划分的依据之一。本文着重阐述了青藏高原古里雅３０９ｍ冰芯中δ^(１８)Ｏ记录研究的一些结果。对于该冰芯上部１２０ｍ，根据δ^(１８)Ｏ等的季节变化特征可划分出２０００多个年层，这是该冰芯高分辨率气候环境记录恢复的基础。借助于放射性物质（３６ＣＩ）测年等手段，建立了该冰芯下部的时间标尺。据此恢复了０．１２５Ｍａ以来古里雅冰芯中１８Ｏ记录，将其与深海沉积中的氧同位素变化相比较，可划分出阶段 １，２，３，４和５，其中阶段５又可划分出 ５个业阶段，即ａ，ｂ，ｃ，ｄ和ｅ亚阶段。古里雅冰芯１８Ｏ记录的一个突出特征就是其升高和降低的幅度都很大，这反映了青藏高原对于气候变化的响应是极为敏感的。５ｅ时古里雅冰芯中δ^(１８)Ｏ所记录的升温幅度达５℃，高于全球平均升温值２～３℃。

The Guliya 309m ice core is the only ice core with the longest length and time span from the middle and low latitudes. It was estimated that the bottom ice of the core formed about 0.76MaB.P. Many ways were used for the ice core dating. Based on the seasonal characteristics of snow and ice chemical compositions and physical features, especially 18O and visible dirty layer, more than 2000 annual snow / ice layers were counted for the upper 120m part of this core. This provided a basis for the reconstruction of the high resolution climatic and environmental records by the Guliya ice core. By means of measurements of radio isotope 36CI and other dating methods, the time scale of the lower part of this core was established. We have reconstructed the variations of 18O in the Guliya ice core since 0.125MaB. P. Comparison with the oxygen isotope records in the deep sea sediment the marine oxygen isotope stages l, 2, 3, 4 and 5 could be discerned in the recent 0.125Ma record of 18O in the Guliya ice core. Furthermore the stage 5 in the Guliya ice core record could be divided into five substages, i.e. 5a, 5b, 5c, 5d and 5e. A remarkable feature of 18O in the Guliya ice core is that the amplitude of its variations is very large, which reflects that the Tibetan Plateau is the most sensitive region to global climatic change. During the time period of 5e, 18O in the Guliya ice core revealed that the temperature was about 5℃ higher than now, which exceeded the global average temperature increase magnitude by 2--3℃. The coming of the last glacial stage is quite abrupt. During the 3000a from substage 5a to stage 4, 18O decreased 7.5‰, corresponding to a temperature decrease of 12℃. In contrast with 18O in Greenland ice core, the amplitude of 18O variations recorded in the Guliya ice core is larger. This may reflect a fact that the Tibetan Plateau where the Guliya ice core is extracted is more sensitive to climate change than that of Greenland. The mechanism is that the cold climate results in thicker, larger and longer--lasted snow cover on the Tibetan Plateau, which can intensify the cooling further. As a result, the cooling magnitude has been amplified. Whereas in Greenland, the surfaces is covered by snow and ice all the times, and therefore, the climate change is less likely being amplified.