中国黄土高分辨率多代用指标研究与季风快速变化

East Asian monsoon, as a key interactive transmitter of high- and low-latitude climate, has played key roles in transporting dust, heat and moisture over the northern hemisphere. Chinese loess is considered as a unique continental archive of past climate change and has been studied intensively to infer the evolution of the East Asian monsoon and its links to regional tectonic and global climatic factors. Numerous studies on Chinese loess and red-clay sequences have focused on the monsoon variability at tectonic-to-orbital timescales and achieved great progresses regarding the tempo-spatial features of monsoon variability and multi-scale monsoon dynamics. However, the magnitude and frequencies of rapid monsoon changes at millennial timescales remain poorly constrained. This proposal will conduct a high-resolution and multi-proxy investigation of Chinese loess to evaluate the features and mechanisms of rapid monsoon changes. By integrated comparison of high-resolution loess-based monsoonal proxies (e.g., scanning XRF-derived elemental geochemistry) with other paleoclimate records from speleothem, ice-core, and marine sediments, our objectives are to provide more reliable proxy records for further modeling test, new conceptual understanding of the natural monsoon variability and dynamics. Our study will permit robust evaluation of the regional response to global climate change and shed new insights into future projection of East Asian monsoon variability.

东亚季风作为高、低纬气候相互作用的关键纽带，在北半球的粉尘和水热传输中扮演着重要角色。中国黄土被视为过去气候变化的典型陆相沉积记录，广泛用于揭示东亚季风的演化历史及其与全球气候和区域构造因素的动力关联。大量的黄土-红粘土沉积序列的研究，提取了构造-轨道时间尺度东亚季风的变率特征，对东亚季风演化的规律和机制有了深刻理解，但针对短尺度季风快速变化的研究仍显薄弱。本项目将以"季风快速变化的特征和机理"为切入点，围绕着中国黄土开展高分辨率多代用指标的研究，包括扫描XRF、粒度、色度和同位素，旨在查明东亚冬、夏季风突变事件的变化特征。通过开展区域季风与全球气候变化相结合的集成研究，为数值模拟提供可信的地质记录检验，提出对东亚季风的自然变率和机理的新理解，进而为科学评估全球环境变化的区域影响和准确预测未来季风变率提供科学依据。

黄土高原西北部高分辨率黄土沉积研究揭示出东亚季风气候存有明显亚轨道尺度的快速波动，与北半球高纬气候和大西洋经向环流变化关系密切。本课题选择黄土高原三个典型剖面（古浪、临夏及邙山）展开研究，利用高分辨率元素比值结合粒度和同位素等代用指标，揭示出最后两个冰期旋回的冬、夏季风快速变化特征，与冰心、石笋和深海记录进行对比，探讨了季风突变事件的区域一致性和遥相关动力过程。结果表明，千年尺度气候事件的变化幅度在不同指标间有明显差异，比如碳同位素变化幅度最大，其次分别为Ca/K、Fe/K、粒度和Si/K等，其归因于这些指标对不同气候要素响应的差异。通过与格陵兰冰心及北大西洋的冰漂碎屑记录(IRD)和中国石笋对比，发现最后两个冰期中黄土多个代用指标揭示的季风快速变化，同冰心与石笋记录中冷暖和干湿波动高度相似，但明显高于北大西洋浮冰碎屑事件的发生频率。粒度变化记录的千年尺度冬季风显著增强与石笋记录的弱夏季风事件有良好对应关系，大幅度的快速变化在最后两个冰期旋回多出现偏冷干的冰期。频谱分析结果表明，东亚季风存在显著8-4kyr和3-1kyr两个周期组分，分别对应于∼6 kyr周期的H事件和以∼1.5 kyr周期的D-O旋回。本研究表明，尽管突变事件是普遍存在于黄土、石笋、冰芯和海洋记录等记录中，但在不同载体和不同指标中的印记是有明显差异的，提高地质记录的测年精度是理解气候突变事件的特征和规律的关键。