青藏高原冰芯稳定氧同位素记录的温度代用性研究

以青藏高原为主体的第三极地区是中、低纬度最大的冰川作用区。冰芯记录可为该地区过去气候环境变化研究提供重要的信息。但在青藏高原地区尤其是高原南部印度季风影响区, 其冰芯稳定同位素记录的解释还存在着不确定性。本文整合青藏高原不同空间位置上的10支冰芯 δ18O记录, 以研究其空间集成的序列与区域温度的关系, 来论证青藏高原冰芯稳定同位素指标的温度代用性。将青藏高原北部和南部各5支冰芯及整个青藏高原面上的这10支冰芯 δ18O记录经Z-score标准化处理后, 与相应区域的器测气温标准化序列进行统计分析。结果发现, 无论是高原北部、高原南部还是整个高原面上, 冰芯 δ18O与气温的标准化序列均存在显著的相关关系。在此统计分析基础上, 将冰芯 δ18O标准化序列延伸至1900年, 从而重建了20世纪青藏高原地区气温变化, 该气温序列与北半球气温变化具有较好的相似性。如上分析表明, 青藏高原冰芯 δ18O记录是区域气温变化的良好代用指标, 多支冰芯 δ18O记录的综合集成能更好地揭示过去气候变化特征。

STUDY ON THE WATER STABLE ISOTOPES IN TIBETAN PLATEAU ICE CORES AS A PROXY OF TEMPERATURE

Centered on the Tibetan Plateau (TP), the Third Pole region contains the highest concentration of glaciers outside of Polar Regions. Ice cores in the TP can provide important information for the paleoclimate and paleoenvironmental research. However, interpretations on the water stable isotope records in Tibetan ice cores, especially in the southern TP where is seasonally influenced by the Indian monsoon, are still somewhat controversial. In this research, therefore, δ18O records of 10 ice cores (Muztagata, Dunde, Malan, Puruogangri, Geladandong, Longxiazailongba, Noijin Kangsang, East Rongbuk-1998, East Rongbuk-2002, and Dasuopu) equally distributed over the northern TP and the southern TP are integrated, respectively, and the relationship between the two composite δ18O records with the respective regional air temperature are discussed. The composite δ18O record of the 10 ice cores is also compared with the instrumental air temperature on the whole TP. The individual Tibetan ice core δ18O records and meteorological station air temperature records are first normalized by Z-score transformation and averaged on the respective geographic regions, and the correlations between the composite ice core δ18O and air temperature are then analyzed during the period 1955~2004 A.D. The results show that the composite δ18O time series over the northern, the southern and the whole TP are all significantly correlated with the respective regional air temperature records at the 99% confident level, with the correlation coefficients of 0.53, 0.44 and 0.57. The correlations are improved when the 5-year running means are used. In addition, the correlations between the composite δ18O record over southern TP and the su mmer monsoon rainfall series over North India, Northeast India and North Central India, and South Asian su mmer monsoon index are also analyzed. The weak and non-significant correlation coefficients of-0.15,-0.05,-0.18 and-0.08 suggest that the annual δ18O record over southern TP is not directly controlled by the Indian monsoon related precipitation amount. The composite ice core δ18O record over the TP is extended to 1900 A.D., and the annual variation of air temperature during the twentieth century is thus constructed based on above statistical relationship. A good correlation (r=0.59, p<0.0001) is observed between the constructed TP temperature and the northern hemisphere temperature. These analyses demonstrate that the water stable isotope records in the TP ice cores are definitely the proxy of air temperature, and that the spatially integrated stable isotope records are much better than the individual in exploring the past regional climate change.