通过降水和冰芯稳定同位素揭示ENSO对“第三极”南北部水汽来源的影响

The Third Pole is the largest ice store region on earth outside the Arctic and Antarctica. In the milieu of global warming, changes occur to the unique geography and geomorphology on the Third Pole, which not only influence human livelihood and social sustainability in the region, but also bear a far-reaching effect on weather and climate in China, Asia, or even the entire northern hemisphere. On the other hand, El Nino-Southern Oscillation (ENSO), as the major driver behind inter-annual climate variability throughout the globe, is interacting closely with large-scale atmospheric circulations such as the Asian Monsoon and North Atlantic Oscillation, and bearing significant impact on East Asian Climate. Yet few efforts have been devoted so far to studying the influences of ENSO on Third Pole environment and climate. We therefore see a need to find in the Third Pole environment an efficient climate proxy to comprehend the issue from both a short- and long-term perspective. Widely considered as an effective moisture tracer, stable water isotopes can be used to reveal land-air-sea interactions and related atmospheric circulation patterns. Given the spatial heterogeneity of precipitation stable isotopic variation in the Third Pole, we plan to add in the current program 4 more precipitation monitoring stations for event precipitation sampling and simultaneous meteorological record taking. Together with the existent 5 stations in the northern and southern Third Pole, this program intends to focus on different isotopic signatures of ENSO in event precipitation and ice core record in, respectively, the northern and southern parts, thus revealing the heterogeneous influences of ENSO on the Third Pole. It will explore possible mechanisms related to the heterogeneous ENSO influences, through correlating precipitation and ice core stable isotopes with major meteorological factors and sea surface temperature, and comparing field observations with synoptic-scale atmospheric models and moisture back-trajectories integrated with reanalysis data. We will re-visit, from the perspective of long-term stable water isotopic responses to ENSO, the past 100-yr ice core stable isotope record of, respectively, the Kuokuosele (38°11.572'N, 75°10.965'E, 5700 m a.s.l.) in the northwest and Zuoqiupu (29°7'N, 96°32'E, 5650 m a.s.l) in the southeast. The purpose is to verify regionally unique ENSO influences on precipitation stable isotope variation features and study the ENSO influences on the Third Pole on a long-term, thus laying a solid scientific foundation for a comprehensive understanding of teleconnections between the ENSO and Third Pole climate.

随着全球变暖，以青藏高原为核心的地球“第三极”作为两极以外冰储量最大的地区，深刻影响中国、亚洲，乃至北半球的气候；而常跟极端天气现象关联的ENSO能影响印度洋和大西洋的海温和温盐环流格局，进而影响“第三极”。但目前关于ENSO对“第三极”不同区域影响的特征与机制尚不清晰。本项目拟通过“第三极”9个站点现代降水稳定同位素的监测，研究ENSO的稳定同位素信号特征，开展南、北部的对比研究，揭示ENSO对不同地区稳定同位素影响的差异与机制；基于代表性冰芯稳定同位素记录，从更长时间尺度上验证稳定同位素对ENSO事件的响应机制，揭示过去100年内ENSO对南、北部降水的影响，为ENSO影响“第三极”气候的研究奠定基础；并结合水汽追踪模型、天气诊断模型和其他环流指标，探索降水和冰芯稳定同位素与水汽来源的关系，尝试探讨ENSO影响“第三极”大气环流的机理，为全面理解ENSO-“第三极”遥相关提供科学依据。

随着全球变暖，以青藏高原为核心的地球“第三极”作为两极以外冰储量最大的地区，深刻影响中国、亚洲，乃至北半球的气候；而常跟极端天气现象关联的ENSO能影响印度洋和大西洋的海温和温盐环流格局，进而影响“第三极”。但目前关于ENSO对“第三极”不同区域影响的特征与机制尚不清晰。本项目围绕ENSO对“第三极”不同区域影响的特征与机制，利用多个站点的实测数据和冰芯记录，结合气象资料、再分析数据和典型事件的历史序列，研究了“第三极”典型站点现代降水稳定同位素的变化特征，以及冰芯稳定同位素与ENSO变化历史的对应关系，并从大气环流和全球海温变化的角度对青藏高原降水和冰芯稳定同位素的响应特征进行了机制的探讨。取得如下重要结果：（1）利用8年日降水实测资料，并应用稳定同位素标准持续研究孟加拉湾季风和南中国海季风的爆发时间，揭示了孟加拉湾（南中国海）季风逐渐减弱（增强）的趋势，并揭示了热带风暴、高原地形和西风带的共同作用对可能导致稳定同位素出现极端低值的特征；（2）发现高原东北部的内陆地区降水稳定同位素反映了不同季风环流系统的影响，高原东北内陆的玉树地区受孟加拉湾季风的影响，而偏东地区的西安则受到东亚季风的影响，并发现孟加拉湾季风从登陆高原到抵达其东北部约需7-10天，而西安降水稳定同位素可以反映出梅雨的影响，当地晚秋降水可能是东部海洋性暖湿气流和蒙古高压相互作用的结果；（3）利用青藏高原西北部冰芯过去100年的稳定同位素记录，揭示了其变化与厄尔尼诺事件的发生存在滞后一年的正相关关系，并发现大尺度环流过程、特别是厄尔尼诺与西风急流的相互作用可能导致该区降水稳定同位素的温度效应增强，表现出高于其他时期的O18–温度的变化梯度。上述认识为理解青藏高原古气候指标的稳定同位素记录提供了新的思路。项目发表3篇SCI论文，其中2篇为第一标注，1篇为第三标注；并发表一套日降水稳定同位素数据资料。