西沙群岛东岛湖泊沉积记录的近1 000年来热带降雨与人类活动历史

Tropical rainfall variations and human activities of last 1 000 years recorded by lake deposits on the Dongdao Island, Xisha Islands

  • 摘要: 近1000年来区域气候变化模式的研究,是在人类活动与自然变率双重影响因素之下,正确预测和评估未来气候变化趋势的基石。众多的气候载体和代用指标, 揭示了热带海洋和季风变化等对中国不同地区气候的影响,但是关于热带区域的降雨特征与季风活动的关系仍然未有清晰的答案。本文选择西沙群岛东岛的牛塘湖泊,以湖泊沉积物的粒度组分含量和环境磁学参数为替代指标,探讨公元1000—1700年热带区域降雨变化规律及岛礁上记载的人类活动历史。结果表明,东岛的降雨受ENSO活动和热带辐合带移动的双重影响,ENSO的频繁活动和热带辐合带向南回撤均会促使热带区域降雨的增多,这一变化与季风气候呈现反向模式。岛上人类活动强盛时期发生在南宋和明代晚期,该时期区域降雨较多,气候湿润。同时,公元1000—1200年和1450—1600年在中国北方发生的两次强沙尘暴事件,在西沙群岛也有相应的记录,反映了北方粉尘物质在空气中长距离运移和沉降的模式。

     

    Abstract: A series of paleoclimate researches have been made in the South China Sea for the past 1000 years, that provided the insights to the understanding of regional climate change pattern and served as the basis to predict and evaluate the future trends of climate change under the joint actions of the human and the nature. Numerous natural archives and proxies are adopted to reveal the climate changes in different regions of China influenced by monsoon and tropical ocean processes. However, due to the lack of high-resolution climate records, our knowledge about the link between precipitation patterns and monsoon variability remains incomplete, particularly in the tropical region. In order to study the rainfall patterns and the history of anthropogenic activities in tropical zones during the time of AD 1000—1700, we studied such proxies as grain-size distribution and magnetic parameters collected from the sediments of the Cattle Pond on the Dongdao Island of the Xisha Islands. The results show that the precipitation on the Dongdao Island is mainly influenced by ENSO activities and the movements of the Intertropical Convergence Zone. Both of the factors will increase rainfall in the study area, which is opposed to the pattern of the Monsoon system. Human activities on the island were vigorous during the Southern Song Dynasty and the Late Ming Dynasty when the climate is humid and rich in rainfall. There are two periods characterized by sandstorms occurred in northern China during the time of AD 1000—1200 and AD 1450—1600 respectively in the Xisha Islands, reflecting the long-distance migration and precipitation of dust by air.

     

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