西沙群岛珊瑚环礁潟湖沉积和大型滨珊瑚块记录的晚全新世风暴活动频率

The damage of strong storm to costal human life and property is gradually serious in the northwest Pacific Ocean. However, human have limited knowledge about their activity rule. Hence, the study of the occur process and rule of strong storm, as well as the relationship with the typical climatic change during the late Holocene has important scientific value to understand and simulate the changing trends of strong storm in the future. Due to the difficulty in preserving the storm signals in costal sedimentary record and dating problem, the records with high resolution are still scarce in this region. The lacustrine sediment of Atoll lagoon, with a high sedimentation rate and precise dating, is the ideal material to reconstruct the paleotempest. In this proposal, we plan to choose Atoll lagoon, Xisha Island of South China Sea (SCS), as the study site. According to the collected surface sample of large Porites coral blocks (were major moved by strong storm, the surface age major indicate the time of death) around reef flat and reef slope, the surface sediment mud and drilling boreholes of this Atoll lagoon, we can get the age framework of borehole and age of large Porites coral block by the U-Th dating and AMS 14C dating methods. Based on the results of the coarse grains size and LOI data of the lagoon boreholes, and combine the ages of a large number of large Porites coral blocks, to reconstruct the high resolution of frequency of paleotempest in the Xisha region, SCS, during the Late Holocene. We hope to reveal the relationship between frequency of paleotempest and the typical climatic change (e.g., Medieval Warm Period, Little Ice Age, and 20th century Warm Period) in this region, and also to reveal the similarities and the differences of different regions of the Northwest Pacific during the late Holocene by comparing with the records of the paleotempest and paleoclimate.

西北太平洋热带海洋的强风暴对沿岸人类生命财产的危害日趋严重，人类对其活动规律认识有限。研究地质、历史时期强风暴的发生过程、规律及其与典型时段气候的关系，对预测气候持续变暖背景下未来强风暴活动的变化趋势等关键科学问题具有重要意义。因受风暴记录在海岸沉积中难以保存和测年等因素制约，该地区的高分辨率地层记录较少，具有高沉积率且能精确定年的环礁潟湖沉积是重建古风暴的理想载体之一。本申请项目拟选取受风暴强烈影响的西沙群岛环礁潟湖为研究载体，以获取潟湖柱状沉积芯和风暴搬运堆积于珊瑚礁上的大型滨珊瑚块样为基础，开展U-Th和AMS 14C定年进而建立精确可靠的年代框架。通过分析潟湖芯的粒度、LOI等关键数据，结合死亡滨珊瑚块表层年龄，高分辨率地重建晚全新世风暴活动频率。对比分析古气候古风暴记录，揭示该海域晚全新世（强）风暴活动的频率特征及其与典型时段气候的关系以及西北太平洋各区域间风暴频率分布的时空异同。

本项目分别于2013年和2015年搭乘学科组西沙综合考察航次，对西沙开展为期2个月的考察采样。采集了大量的西沙群岛潟湖芯、表层砂以及风暴石样品。在实验室对这些样品开展测年、实验以及数据分析等工作。羚羊礁5.6 m潟湖芯沉积记录了4.2 ka以来的风暴活动。4.2-3.4 ka时段较弱的水动力强度对应于4.2 ka冷事件，风暴活动整体较弱，但波动较大；3.4-0.45 ka时段风暴活动逐渐增强；小冰期以来，西沙海域的风暴活动快速减弱。而在过去的几十年，西沙海域的风暴活动有快速增强趋势，这可能对应于工业革命以来大气CO2浓度快速增加、全球温度上升。采集于西沙海域的29个表层保存完好的风暴石样品记录了过去540年的强风暴活动，其中4个大约形成于1961-1965AD的风暴石可能与1960-1965AD时段影响西北太平洋风暴活动显著增多有明显的对应关系。本项目获得的晚全新世风暴活动以及过去540年的强风暴活动记录，能够为目前国家正在进行的南海大规模工程建设的选址、设计等提供重要的参考。