近千年来中国海岸沙丘演化的时空分异特征

It is of important theoretical and practical significance to advance our understandings for the responses of regional characteristics to global change, which can shed lights on their responses to different scenarios of global warming and sea level rise. Over the past millennium, there are characteristic periods, such as the medieval warm period (MWP) and little ice age (LIA). Jointly influenced by East Asian Monsoon and sea level changes, multi-stages coastal dunes occurred in sandy coastal zones in the coast of China due to suitable wind, wave, sand source and landform conditions. Therefore coastal sand deposition is considered important proxy to record environmental information of China's coast in response to global change for the past millennium. Due to the lack of accurate calibration of absolute age of the coastal sand sedimentary sequence, it is still difficult to evaluate the two characteristic climate period of spatiotemporal diversity and the responses of China’s sandy coastal zones in response to global change on centennial scale. This project plans to study the coast of Changli in Hebei province, the southeastern coast of Fujian province and the northeast coast of Hainan Island, which are three typical coastal sand dunes for our research aims. We will use aeolian geomorphology, coastal sedimentology and quaternary chronology methods to comprehensively investigate the source of the sand for modern coastal dunes, spatial variation and seasonal variation characteristic of sand granularity on the surface of coastal dunes characteristics. We will identify the spatiotemporal characteristic of modern coastal dynamic process via the sedimentary structure observation and sensitive granularity parameters analysis of typical coastal dune profiles. Variations of environmental changes over the past millennium will be extracted from measuring the proxies from the inter-dunes pit profile and coastal wetland shallow sedimentary core. The sea level changes will be inferred from staggered distribution signal of coastal zone buried dune sedimentary on typical sections, which will be obtained from interpretation of the image obtained from the high resolution ground penetrating radar (GPR). The chronologies of the sedimentary cores over the past millennium will be established based on the cross-checking the OSL dating with sands of typical coastal dunes, pits and shallow hole section, as well as AMS14C dating and in environmental archaeological sites. Via division and comparisons among sand deposition sequence of three typical regions, we will establish the time series and the chronology framework of sandy coast sedimentary environment in China. We will explore the factors on the formations of the sand dunes in relation to the evolution of the eastern Asian monsoon, sea-level change and human activities with special attention being paid on the MWP and LIA priods. We will figure out spatiotemporal evolution of the coastal dunes in East Asian Monsoon region on centennial scale.

近千年来的中世纪暖期（MWP）和小冰期（LIA），东亚季风和海平面发生明显变化，我国砂质海岸带发育了多期海岸沙丘，但因缺乏精细年代的海岸风沙沉积序列，目前尚难在百年际尺度上解析两个特征期海岸沙丘演化的时空分异规律。本项目选择河北东部海岸、福建东南海岸和海南岛东北海岸三个典型的海岸沙丘分布区，在综合考察现代海岸沙丘地貌过程的基础上，依据丘间地剖面环境代用指标采样测试及探地雷达（GPR）探测解译沉积构造分析，获取特征期海岸气候环境和海平面变化信息；以石英砂OSL测年为主结合有机碳AMS14C测年校验建立年代标尺，以海岸风沙粒度参数为代用指标，重建高分辨率的区域海岸风沙沉积序列。通过三个区域海岸风沙沉积序列的划分与对比，在百年际尺度上重建近千年来海岸沙丘演化的时空序列。从陆海气相互作用维度，探讨东亚季风演变、海平面变化和人类活动对我国海岸沙丘演化的驱动机制，为海岸带可持续发展与管理提供理论支撑。

近千年来东亚季风和海平面发生明显变化，我国东部砂质海岸带发育多期海岸沙丘，但因缺乏精细年代控制，尚难在百年尺度上解析海岸沙丘演化的时空分异规律。本项目选择河北东部、福建东南部和海南岛东北部砂质海岸带，选取典型海岸风沙沉积剖面、人类文化遗址剖面等，以石英砂OSL测年为主结合AMS14C测年校验建立年代标尺，以风沙粒度参数、考古文化发展期为主要代用指标，在百年际尺度上重建高分辨率的区域海岸风沙沉积序列，重建近千年来中国东部海岸沙丘演化的时空序列。项目实施以来有以下新发现：.（1）河北昌黎海岸高大海岸沙丘是近300a的小冰期后期以来发育的。近60年来，海岸沙丘分布规模和沙丘大小呈现风蚀消减特征，由于同期区域风力和干湿变化的气候效应大体相抵，而海岸带固沙造林、人工植被覆盖面积持续扩大，因此植树造林、防风固沙等人类活动是导致区域沙丘规模缩减的主要原因。.（2）近2000年以来，福建东南沿海的风沙活动周期与东北亚及西北欧海岸具有总体上一致的特点，反映了彼时北半球范围的气候变化具有大体一致的阶段性特征。而各个区域风沙活动周期起止时间的不同，反映了各地所处大气环流系统位置或是地方性因素的差异。.（3）中国东部海岸环境变化对砂质海岸带史前人类活动有重要影响。福建沿海遗址文化层记录的古人类活动期与华南沿海其他文化期的发展变化基本上是同步的。总的来看，海平面升降变化直接影响了海岸带人类活动空间和栖息地选址，而近千年来不断增强的冬季风，可能是造成福建海岸带文化遗址衰落的重要原因之一。.（4）海南岛东北部海岸与其他纬度带风沙活动的变化趋势是一致的，但风沙活动强度峰谷值变化呈现一定的相位差，反映了中国东部海岸风沙活动既受到北半球太阳辐射能量变化的共同驱动，同时各地受冬季风波及范围、海平面升降差异、沙源供给条件等不同尺度因素的耦合作用，这是各地海岸沙丘发育呈现时空差异性的主要驱动因素。