水汽来源和输送过程对我国典型东亚季风区大气水汽和降水稳定同位素的影响研究

It has been a long time that local “Amount effect” of stable isotopes in precipitation is the theoretical basis for reconstructing paleoclimate by stable isotopic records in stalagmites and other media from monsoon regions of low-mid latitudes, however, which has been questioned in recent years. More and more observations and simulations of water stable isotopes show that non-local factors of moisture sources and water vapor transport can influence isotopic compositions of atmospheric vapor and precipitation in monsoon regions significantly. It is known that isotopic composition of atmospheric vapor is a good indicator for moisture sources and water vapor transport. With the recent advent of laser spectroscopy technology for stable isotopes measurements, the in-situ and high temporal resolution measurements of stable isotopes in atmospheric vapor have become possible. Based on the in-situ and high temporal resolution observations of stable isotopes in vapor and precipitation at the Station for Observing Regional Processes of the Earth System (SORPES) at Nanjing University as well as three stations located in air mass trajectories of the East Asian summer monsoon, combing with the simulations of water stable isotopes from the LMDZ general circulation model (LMDZiso), we plan to investigate the effect of different moisture sources in different seasons and the summer upstream convection processes along the air mass trajectories on isotopic composition of atmospheric vapor and precipitation over the typical East Asian monsoonal region of China. The results of our study could provide the rationale for quantitative interpretations of stable isotopic proxies of paleoclimate in the monsoon region.

长期以来局地“降水量效应”是中低纬度季风区石笋等稳定同位素记录古气候重建的理论基础，但是近年来“降水量效应”受到了较大的质疑。近期越来越多的水稳定同位素观测及模拟结果表明，非局地因素水汽来源及其输送过程对季风区大气水汽及降水稳定同位素影响显著。大气水汽稳定同位素可以较好地指示水汽来源及其输送过程，近期随着激光光谱稳定同位素分析技术的出现，使原位高分辨率大气水汽稳定同位素观测工作成为了可能。本项目基于南京大学地球系统区域过程综合观测试验基地（SORPES）以及东亚夏季风期间水汽输送通道上三个站位原位高分辨率大气水汽及降水稳定同位素观测数据，结合大气环流稳定同位素模型（LMDZiso）模拟结果，重点研究不同季节水汽来源以及夏季上游水汽输送通道上对流过程对典型东亚季风区大气水汽及降水稳定同位素的影响，研究结果可为本区石笋等稳定同位素记录古气候定量重建研究提供理论依据。

本项目主要基于南京大学地球系统区域过程综合观测试验基地（SORPES）大气水汽及降水稳定同位素长期高分辨率观测数据，重点研究不同季节水汽来源以及夏季上游水汽输送通道上对流过程对典型东亚季风区大气水汽及降水稳定同位素的影响，得到如下几点重要研究结果：1）根据水稳定同位素示踪原理，结合大气水汽输送模型，发现典型东亚季风区夏季（6-9月）水汽主要来自热带海洋大陆-南海-中国东南部水汽通道的水汽输送，春季水汽主要来自局地及中国近海，而秋冬季节水汽主要来自北方内陆再循环的水汽。2）考虑不同水汽源区水汽输送至降水站点时间的差异以及具体的水汽输送通道，发展了一种准确确定上游对流淋洗关键区的新方法（简称UKRRI）。3）利用UKRRI方法，发现热带海洋大陆-南海-中国东南部水汽输送通道上的对流淋洗过程是影响东亚季风区夏季大气水汽及降水同位素变化的主要因素，这显著不同于过去多数研究认为上游印度洋地区对流过程是影响东亚季风区降水稳定同位素变化的观点。本项目研究结果对于东亚季风区石笋、树轮等稳定同位素记录的解释及气候重建具有重要意义。