中文摘要：

　海南岛东岸和南岸两个礁区采集了3个活结滨珊瑚，沿珊瑚生长轴线切样进行月分辨率的氧碳同位素分析，目的是研究珊瑚碳同位素组成在季节、年际和年代际3个时间尺度上的变化与季风气候的联系。结果表明，珊瑚的δ^18O的值的季节性变化和年际变化在全年都基本上受表层海温的控制，基于这一相关变化可以建立同位素序列的时间标尺。在同位素的时间序列上，珊瑚δ^13C值季节性变化与日照基本同步。由于日照变化主要受大气顶部太阳理论日照和云量变化的控制，而理论日照在某一地点随时间的变化是规律的，所以，云量变化是珊瑚碳同位素组成季节变化的主要因素。过去30年珊瑚δ^13C值最明显的年代际变化特征是1986—1987年δ^13C值的突然减小事件，这一事件与日照的变化在时间和统计特征上都有一致性，但与云量变化关系不大，可能与其他因素引起的日照变化有关。现代滨珊瑚碳同位素组成普遍存在着变小的趋势，这种年代际变化与大气CO2同位素变化一致，两者在机理上成因关系也说明，近代珊瑚碳同位素组成变小的趋势与大气CO2的变化有关。不同海区的珊瑚同位素记录对比显示，海水及其中的有机物的碳同位素组成决定着珊瑚δ^13C值季节变化性在空间上的分异特征，它们在很大程度上受淡水注入量的影响；同时，日照起主要作用的光合作用也对珊瑚δ^13C值的变化在空间上的分异有一定的贡献。

英文摘要：

Coral colonies of Porites lutea and P. lobata were collected from the eastern and southern offshore areas of the Hainan Island in the South China Sea. Oxygen and carbon isotope ratios were analyzed along the main growth axis of the coral colonies at monthly resolution in order to investigate seasonal, annual, and decadal trend of coral δ^13C variations as well as their association with monsoonal climate. The results indicate that seasonal variation of coral δ^18O is mostly controlled by sea surface temperature. Based on a time scale constructed from the correlation of coral δ^18O and sea surface temperature, seasonal changes of coral δ^13C are found to be in phase with solar radiation. We therefore suggest that light induced photosynthesis may modulate most of seasonal features of coral δ^13C. Since solar radiation is mainly determined by cloud coverage, the association between coral δ^13C and solar radiation enables us to reconstruct seasonal and annual variation of solar radiation and cloudiness when astronomical effect is considered. A remarkable decadal trend of coral δ^13C record of the past 30 years is the abrupt decrease of annual minimum around 1987, resulting in a decreased amplitude of annual fluctuation. This coral δ^13C shift corresponds statistically with local solar radiation record. At the same time, there is a generally decreasing trend of coral δ^13C over the past 15 years. This trend is consistent with seawater composition indicated by salinity, and is best explained as the consequence of changes in atmospheric CO2 concentration. The spatial differentiation of seasonal fluctuations of three coral δ^13C records is characterized by a lower annual minimum, lower mean value, and larger annual amplitude at Qionghai to the offshore east of the Hainan Island; and by a higher annual minimum, higher mean value and smaller annual amplitude at Sanya to the offshore south of the Hainan Island. Comparison with marine environmental changes supports the suggestion that these spatial differences are m