巢湖沉积记录的末次冰盛期-早全新世气候事件及响应机制研究

Understanding the rule or mechanisms of climatic events and environmental changes in the Late Quaternary, as well as the quantitative reconstruction of the climate in the past, are important factors to help us recognize changes in climatic patterns against the background of global warming. Based on the systematic analysis of sedimentology and stratigraphy, combined with a precise and reliable chronological framework using dating methods such as AMS14C, etc., this project intends to select the Chaohu long-borehole core as its main research material, which completely covers the Last Glacial Maximum to the early Holocene at the south-north transition belt in the eastern monsoon region of China, to establish a high-resolution sequence of climatic environmental changes by giving priority to pollen records and carbon-nitrogen geochemical analysis, taking XRF and grain size as supplementary information in analyzing the performance of climatic events and characteristic time periods in this region, especially the characteristics of dry-wet variability and water heat distribution. Moreover, based on the database of surface soil pollen in East Asia, this project will use the results of analysis of different sediments and surface soil pollen in the basin to compare and establish a pollen-vegetation-climatic relationship model and quantitatively reconstruct the past climate change. At last, this project will carry out comparative analysis on the high-resolution records and the simulated results from East Asian monsoon region, southwest monsoon region and other parts of the world, and discuss the regional differences of each characteristic period and main climatic events during the Last Glacial Maximum - the Early Holocene, and their mechanisms in response to the East Asian monsoon. This project will provide a new scientific basis for climate predictions, regional response to, and human coping with global changes.

理解晚第四纪气候事件与环境变化的规律和机制、实现过去气候定量化重建是认识未来全球变暖背景下气候格局变化和降低其预估不确定性的重要方面。本项目拟选择中国东部季风区南北过渡地带完整涵盖末次冰盛期-早全新世的巢湖长钻孔岩芯为主要研究材料，在系统的地层学、沉积学分析基础上，利用AMS14C等测年方法建立精确可靠的年代框架；以孢粉记录和碳氮地球化学分析为主，XRF、粒度等为辅建立高分辨率气候环境变化序列，重点分析气候事件和特征时段在本区的表现，特别是干湿变幅及水热配置特征；在东亚表土孢粉数据库基础上，利用流域内不同沉积物和表土孢粉分析结果，对比建立孢粉-植被-气候关系模型，定量重建古气候；与东亚、西南季风区和全球其它高分辨率记录及气候模拟资料对比分析，探讨末次冰盛期-早全新世各特征时段和主要气候事件的区域差异及其对东亚季风的响应机制。本项目将为全球变化区域响应及应对、气候趋势预测提供新的科学依据。

以多个巢湖长钻孔岩芯为研究对象，利用AMS14C和OSL构建年代序列，通过开展高分辨率沉积物粒度、磁组构、元素、孢粉和微炭屑等代用指标气候环境意义的综合研究，重建了巢湖末次冰盛期-早全新世气候事件序列及古环境演化史，并对比探讨了环境变化的响应机制。结果表明：1）巢湖末次冰盛期25.8-16.1 cal. ka BP为浅湖环境，气候极端干冷；16.1-14.8 cal. ka BP持续干冷，仍为浅湖环境，记录了H1事件；14.8-12.8 cal. ka BP为浅湖环境，气候环境响应博令/阿勒罗德暖期总体由干冷转向温凉；12.8-11.6 cal. ka BP，遭受西侧大别山掀斜运动，沉积环境由浅湖向滨湖、湖泊三角洲过渡，气候干冷，是对新仙女木事件的区域响应；早全新世初11.6-10.5 cal. ka BP气候干冷，为滨湖-湖泊三角洲环境，间歇性河流发育；10.5-7.5 cal. ka BP仍为滨湖-湖泊三角洲环境，气候由干冷向暖湿过渡，降水增多，湖泊水位开始回升、面积扩张。2）巢湖沉积完整记录了末次冰盛期-早全新世发生的H1、阿勒罗德内部冷期、新仙女木、11.1 ka BP、10.5 ka BP、9.3 ka BP、8.2 ka BP等气候干冷事件，以及末次冰盛期晚期降水增多、博令、阿勒罗德等气候暖湿事件。3）巢湖末次冰盛期-早全新世气候事件与古环境变化揭示出潜在的气候变化驱动机制，即北半球夏季太阳辐射增强（减弱）可能为触发机制，触发北半球高纬冰量消融（增加）变化；在万年尺度（轨道尺度）上，北半球高纬冰量消融（增加），导致赤道辐合带北进（南移），从而导致东亚夏季风增强（减弱），区域气候暖湿（冷干）；在千年尺度（亚轨道尺度）上，随着北半球高纬冰盖消融，大量以冷水和冰筏碎屑形式的淡水注入北大西洋，导致北大西洋温盐环流减弱、赤道辐合带南移，引起东亚夏季风减弱，区域气候变干冷。