【作者】 苏瑞侠；

【导师】 朱照宇；

【作者基本信息】 中国科学院研究生院（广州地球化学研究所） ， 地球化学， 2006， 博士

【摘要】 本论文在海南岛东岸和南岸采集了滨珊瑚进行生长参数和氧碳同位素组成研究。用实测和数字图像分析方法对珊瑚生长层和生长参数的测量结果表明,南海北部的滨珊瑚存在年、半年、季和月四种级别的生长层,它们大多与光照的相应的变化周期有关;在大多数情况下;以3月下旬至4月中旬或6月下旬至9月中旬的季层高密度带为年最高密度带,最低密度带形成于4月下旬至6月中旬;珊瑚生长参数变化趋势是近几十年来密度减小、生长率增大,这一特征最明显地发生于最近20年,其中突然的变化是1986-1987年,这一趋势与近年来全球升温和大气CO₂增加趋势是一致的;多数珊瑚钙化率近几十年有减小的趋势,这可能与CO₂增加有关。综合分析认为,光照、温度、大气CO₂和水深等因素在南海北部珊瑚生长中起着重要作用。 氧同位素分析结果表明,滨珊瑚的δ¹⁸O值季节和年际变化在冬季风盛行的季节里主要受表层海温控制,而在夏季δ¹⁸O值与表层海水盐度显示较好的相关性。海水的盐度和同位素分析结果显示,它们都与夏季风降水量相关,指示着夏季风降水对海水和珊瑚氧同位素组成季节与年际变化的决定性作用。在年代际趋势变化上,珊瑚δ¹⁸O值与大区域的盐度变化相一致,并且与当地降水关系不大,可能说明了珊瑚δ¹⁸O值年代际变化受大区域海洋环流和水文气候影响。珊瑚δ¹⁸O值空间变化与海水盐度和降雨量的变化一致,可能说明了主要受大区域降雨和淡水注入控制的海水成分对南海北部珊瑚δ¹⁸O值空间变化的主导作用。 珊瑚δ¹⁸O和δ¹³C值季节性变化明显失调,而珊瑚δ¹⁸C值与日照的季节性变化基本上同步并存在明显的相关性,这些特征说明了日照通过影响光合作用在很大程度上决定着珊瑚碳同位素组成的季节变化;过去30年珊瑚δ¹⁸C值最明显的年代际变化特征是1986-1987年间突然减小,这与光照的变化在时间和统计特征上都有一致性,但这一突变与云量变化关系不大,可能与光照变化有关。近几十年珊瑚δ¹⁸C值存在着明显变小的趋势,这与大气CO₂碳同位素变化趋势一致,指示了大气CO₂变化对珊瑚碳同位素组成变化趋势的作用。更多还原

【Abstract】 Coral colonies of Porites lutea and P. lobata were collected from areas to the east and south offshore of Hainan Island, South China Sea （SCS） to investigate the influence of monsoonal climate on coral growth and isotopic compositions.Annual, semiannual, seasonal and monthly growth bands were found in the massive corals of Northern SCS. The highest density bands within an annual band were developed from the last ten days of March to the middle ten days of April or from the last ten days of June to the middle ten days of Septemp, while the lowest density bands are formed from the last ten days of April to the middle ten days of June in an annual band. Coral skeleton density has decreased and the linear extension has increased during the past decades. Statistic indicate that calcification of most coral has decreased in the past decade due to arising of atmospheric CO₂ concentration. It’s demostrated that the available light for photosythesis of zooxanthellate within scleractinian coral is most important variable to influence coral linear extension and the skeleton density. Meanwhile, the temperature and atmospheric CO₂ have the significant effects on the trends of coral density, linear extension and calcification.Oxygen isotope ratios, ¹⁸O/¹⁶O, were analyzed along the major axis of growth at a resolution of 25-28 samples within an annual band from three colonies. Coral δ¹⁸O value correlates well with sea surface temperature （SST） throughout most years, particularly when the Asian winter monsoon prevails over the region. It is estimatedthat most of the seasonal features of coral 518O values are controlled by changes in SST with a significant contribution of SSS. This indicates the importance of temperature, as determined by the Asian winter monsoon, as a control on seasonal coral 518O value variations in the South China Sea. Given the fact that annual SSS maxima show minor inter-annual changes, the inter-annual change of annual coral 518O maximum mainly reflects the SST induced by the winter monsoon. While the coral 818O values is mainly controlled by SST, deviations of the 8I8O values from SST correlate statistically with sea surface salinity, particularly for summer extreme events when SST reaches its annual maximum with minor inter-annual change. Therefore, we suggest that the inter-annual variation of the annual coral 8I8O minima is mainly controlled by seawater composition. Seawater composition analysis indicates that its 818O values and salinity are simultaneously affected by freshwater inputs primarily from precipitation, which is mainly supplied by the Asian summer monsoon. The three coral records consistently reveal clear inter-decadal trends in 818O values - a gradual increase from 1968 to 1987, and a subsequent decrease from 1987 to 2003. These inter-decadal trends are roughly consistent with salinity changes - but not with temperature and precipitation, suggesting that seawater composition controlled by freshwater inputs from distant source areas, rather than from local precipitation, is responsible for the trends in seawater composition and coral 518O values over the last 30 years. Comparison of the three coral records indicates that spatial variations in coral 518O values coincide with variations in seawater salinity and local precipitation, but not with temperature. This confirms the dominant role of seawater composition, mainly controlled by monsoonal precipitation, on the spatial variability of coral 818O values in the South China Sea.Based on a time scale constructed from the correlation of 818O values and sea surface temperature, seasonal changes of the coral 8I3C values are in phase with solar radiation, and regression analysis demonstrates their close correlation. Therefore, it’s suggest that light-induced photosynthesis modulates most of the seasonal features of the coral S13C values. A remarkable inter-decadal trend of the coral 8I3C values record of the last 30 years is the abrupt decrease of the annual minimum of around 1987,resulting in a decreased amplitude of annual fluctuation. This coral 613C values change shift corresponds statistically with the local radiation record, suggesting a causal effect. At the same time, there is a generally decreasing trend of coral 513C values over the last 15 years. This trend is consistent with seawater composition as indicated by salinity, and is best explained as the consequence of changes in atmospheric CO2 content. The spatial differentiation of the seasonal fluctuations of the three coral 8I3C values records is characterized by a lower annual minimum, lower mean value, and larger annual amplitude at Qionghai to the east offshore of Hainan Isalnd;and by a higher annual minimum, higher mean value and smaller annual amplitude at Sanya to the south offshore of Hainan Island. Comparison with marine environmental variables supports the suggestion that these spatial differences are mainly the result of differences in seawater composition in the two regions.更多还原