南海西沙永乐群岛海鸟古生态变化过程的稳定同位素研究

我们前期工作已恢复出西沙东岛和甘泉岛过去2000年海鸟数量变化记录，但对海鸟数量变化的原因和机制尚不清楚。利用不同生物组织的同位素组成来解读这种机制是本研究的核心内容，国内目前这方面的研究比较薄弱。本项目将在已有的工作基础上，重点对西沙永乐群岛典型岛屿海鸟粪土沉积层中保存完好的生物遗迹（如鸟粪、鸟骨、鱼骨、蛋壳等）进行稳定同位素分析，根据同位素生态学理论恢复海鸟食谱和取食行为等宏观的生态环境变化的历史记录，在与海鸟数量波动和气候变化记录的对比基础上，阐明永乐群岛海鸟古生态对气候变化的响应机制，并从历史角度区分不同时期气候变化和人类活动对海鸟生态变化过程的影响，最终回答永乐群岛历史时期海鸟数量变化甚至近现代几乎灭绝的真正原因。研究结果将有助于深入认识"气候-海洋-海鸟-海岛"之间的生物地球化学循环过程，并为评估全球变暖背景下珊瑚岛生态系统的脆弱性及预测未来可能的生态环境变化提供科学资料。

The historical records of seabird population on the Dongdao Island and Ganquan Island of Xisha Archipelago,South China Sea over the past two millennia have been reconstructed in our previous studies. The complex processes that alter or maintain seabird population, however, still remain unclear. To understand these processes, we must examine the possible mechanisms that cause changes in seabird population, by characterizing stable isotopic signatures recored in the ancient bird tissues. A large number of fossil bird remains (e.g.guano particle, fish/bird bone, eggshell etc.) were found to be well preserved in the ornithogenic sediment sequences on the Yongle Islands of Xisha archipelago. In the proposed project, we will focus on the analysis of stable isotopic compositions in these well-preserved bird remains, and consequently reconstruct the records of historical seabird population, seabirds'palaeo-diet and foraging strategy. By compare and contrast between seabird population and local/global climate records, we will be able to decode how climate changes impacted seabird population, and evaluate how the eco-environment of seabird-inhabited coral islands were modified in response to these changes. Identifying the different roles of climate and anthropogenic activities in influencing ecological processes of seabirds will help us clarify the ultimate reasons for the past seabird population changes, as well as for its recent rapid recession even to almost extinction on the Yongle Islands. This project will provide much needed information about how best to interpret the biogeochemical interplay between the ocean, the oceanic islands, the biosphere, and climate. Also, the results of the proposed project will be helpful for assessing risks of global warming on fragile coral island ecosystems and for predicting future eco-environmental changes.