全新世亚洲中部降水氧同位素与气候变化的模拟研究

Stable isotopes of oxygen are components of the water molecule, which are ideal natural tracers for describing the phenomena of water cycle and therefore are widely used to reconstruct the paleoclimate. However, the climatic interpretation of oxygen isotopic composition (δ18O) in precipitation remains controversy, resulting in large uncertainties in proxy record implications. This project plans to simulate the oxygen isotopes in precipitation and climate change during the Holocene using the NASA-GISS ModelE isotope-enabled general circulation model forced by Earth's orbital parameters, greenhouse gas concentrations, continental ice sheets and meltwater fluxes, and their integrations during the Holocene (three time slices: 0 ka, 6 ka and 11 ka). We aim to investigate the key impact factors affecting precipitation δ18O in Central Asia during the Holocene by comparing precipitation δ18O with the precipitation, temperature, evaporation, vapor source, transport route, and other factors. Meanwhile, we will investigate the response of precipitation δ18O during the Holocene to external forcing factors (Earth's orbital parameters, greenhouse gas concentrations, continental ice sheets and meltwater fluxes). In addition, possible physical mechanisms are also to be explored to understand how these external forcing factors influence the precipitation δ18O. This project will provide insights into the climatic significance of precipitation δ18O in Central Asia during the Holocene, and therefore provide reference for paleoclimate reconstruction in Central Asia. Ultimately, this project will provide further insights into climate changes in Central Asia during the Holocene and associating physical mechanisms.

氧同位素是被广泛应用的揭示水循环过程的天然示踪剂，是古气候重建的重要替代指标。然而，目前对降水中稳定氧同位素比率(δ18O)气候意义及其古气候重建结果还存在分歧。本项目拟利用引入稳定同位素循环的GISS ModelE模式，对全新世进行包括轨道参数、温室气体、大陆冰盖和北大西洋淡水注入强迫下的数值模拟试验，分析亚洲中部降水δ18O与降水量、温度、蒸发量、水汽来源和水汽路径等气候因子的关系，探讨该区域降水δ18O的主要影响因子。同时，分析亚洲中部降水δ18O对不同强迫因子的响应特征，以及这些强迫因子是通过哪些机制影响降水δ18O，从而理解全新世亚洲中部降水δ18O的变化原因。以上工作的开展，有助于从气候动力学角度理解全新世亚洲中部降水δ18O的指示意义，为古气候重建提供参考，加深对亚洲中部全新世气候变化及物理机制的理解。

氧同位素（δ18O）是研究过去水循环过程和重建古气候变化的重要替代指标。然而，目前对全新世以来亚洲中部地区降水（石笋）δ18O气候指示意义及其古气候重建结果还存在很大争议，使得我们对亚洲中部地区全新世气候变化过程及其物理机制还缺乏深入理解。本项目利用引入稳定同位素循环的iCESM和GISS-ModelE模式，对全新世开展包括轨道参数、温室气体浓度、陆地冰盖和北大西洋淡水注入强迫下的气候数值模拟试验，结合现代气候观测/再分析、全球大气降水同位素观测网降水δ18O观测和石笋δ18O重建等资料，分析发现全新世亚洲中部降水（石笋）δ18O的变化主要受控于水汽输送过程。在早—中全新世，亚洲中部降水水汽主要来自于远距离的西风输送，降水（石笋）δ18O偏轻，降水较弱；在晚全新世，除西风水汽外，由于东亚夏季风的减弱，有较多来自于近距离亚洲夏季风的水汽沿着青藏高原东缘和北缘输送到亚洲内陆区，降水（石笋）δ18O偏重，降水较强。因此，全新世以来偏重的石笋δ18O揭示了亚洲内陆区逐渐变湿的过程，主要受控于西风与东亚夏季风的相互作用过程。此外，过去几十年我国西北地区的暖湿化也受控于西风与东亚夏季风相互作用过程。本项目的研究成果为全新世亚洲中部干湿变化提供重要的机制解释，也为当前我国西北暖湿化现象做出了科学的解释。