【作者】 徐建；

【导师】 汪品先；

【作者基本信息】 同济大学 ， 海洋地质， 2004， 博士

【摘要】 大洋钻探（ODP）1143站（9°21．72′N，113°17.11′E，水深2，772米）997个样品中浮游有孔虫群的研究，揭示了210万年来南海南部高分辨率（约2千年）的古海洋学变化历史，展示了碳酸盐溶解与保存、海水表层温度、温跃层深度、古生产力以及浮游有孔虫主要属种在冰期-间冰期和长时间尺度上的变化，以及对东亚季风和热带气候演化的响应。此外，本文还对比了第四纪ODP 1143和1146站浮游有孔虫主要属种、温跃层以及古生产力，据此讨论冰期／间冰期东亚冬、夏季风交替强化和海平面升降作用下的南海南北上部海水环境分异的情况。浮游有孔虫碎壳率、绝对丰度、抗溶种百分含量、碳酸盐含量以及粗组分（＞63μm）含量被用于指示碳酸盐的溶解和保存状况。结果显示碳酸盐溶解高峰出现在间冰期至冰期的过渡期；而在冰期至间冰期的过渡期碳酸盐的保存最好。因此推断ODP 1143站的碳酸盐旋回受深海溶解作用和陆源物质稀释作用的共同影响。交叉频谱和相位分析显示所有溶解和保存指标均与底栖有孔虫氧同位素在地球轨道偏心率和斜率周期上强烈相关，并且碳酸盐保存的最大值领先于全球冰量最小值(δ¹⁸O最轻值)，而溶解的最大值滞后于全球冰量最小值。运用FP-12E、SIMMAX-28（专适于南海的现代类比法）以及ANN（神经网络）等技术和方法估算了古温度，并对结果进行了评价。估算结果显示冰期时的海水表层温度总体比间冰期的高。经分析，这可能是由于优势种的变化而致，也说明基于浮游有孔虫统计数据的定量估算温度的方法至少在ODP 1143站不可用。在其他的独立于浮游有孔虫统计数据的定量估算方法建立之前，表层温水种Globigerinoides sacculifer和Globigerinoides ruber的比值被用来定性地指示温度的变化。G．sacculifer／G．ruber比值与底栖有孔虫δ¹⁸O的交叉频谱和相位分析显示，在偏心率、斜率以及23-千年和19-千年的岁差周期上，海水表层温度的最大值均超前于全球冰量最小值。此外，G．sacculifer／G．ruber比值的频谱还显示了很强（超过90％的可信度）的半岁差周期。因此，热带过程可能在南海南部海水表层温度变化中起到了重要的作用，而非全球冰量的控制。温跃层深浅和古生产力高低与东亚季风的强弱变化密切相关。温跃层深度用浮游有孔虫混合层属种组合、温跃层属种组合以及转换函数计算结果来指示。此次工作中对Timor海MD01-2378孔非共生种（asyrnbiotic species）和共生种（symbiotic spedes）的分析，证实其比值是一个很好的生产力指标。ODP1143站的结果显示，冰期时南海南部温跃层较深，生产力也相应较低，间冰期时则反之。指示冰期时冬季风加强而间冰期时夏季风强盛。长时间尺度上，温跃层深度和生产力变化在165万年和85万年时出现明显转折，很可能是对东亚季风阶段性演化的直接响应。周期性变化上，除了斜率（41千年）的主导地位外，温跃层和古生产力还显示了非常突出的半岁差周期，揭示热带气候因素和东亚季风对南海南部上部水体结构变化的共同作用。G．tuber、G．saccutifer、Neogloboquadrina dutertrei、Pulleniatina obliquiloculata和Globorotalia menardii等五个种为1143站的优势种，平均占据了浮游有孔虫群的75.3％。G．ruber、G．sacculifer和N．dutertrei的冰期旋回受碳酸盐溶解、温跃层深度、温度和生产力的共同影响。G．tuber在长时间尺度上与N．dutertrei呈镜像变化，分别在160万年和85万年时出现明显转折，可能反映了温跃层和生产力的重大改变。过去210万年来的G．sacculifer的丰度总体变化不大，主要是由于该种对温跃层变化的随机适应所致。G．menardii和P．obliquiloculata均为热带抗溶种，且都生活在温跃层中，但二者在南海南部记录中的表现却迥异。G．menardii呈现明显的冰期旋回，间冰期的含量比冰期的高。除了温度和溶解作用等影响因素外，南海南部温跃层的冰期-间冰期变化应当是主要的控制因素。P．obliquiloculata虽然也具明显的冰期-间冰期变化，但在中更新世革命以来，与氧同位素记录相反，即含量在冰期时比间冰期时高。对比了西太平洋边缘海地区P．obliquiloculata的柱状样资料，发现该种与氧同位素记录相反的变化只在南海南部出现。而中更新世革命之前，P．obliquiloculata的含量总体在间冰期时高．P．obliquiloculata在中更新世之后冰期时的高含量可能是由于区域性的海水盐度增加、南海南部与热带西太平洋表层海水交换切断所致，也不排除冰期时在南海南部存在着与现代热带西太平洋相似的表层海水环境的可能。另外，有趣的是，表层暖水种粉红色G．ruber在南海南部的冰期旋回也表现出了与其他海域截然相反的变化，其在冰期和间冰期较冷的阶段含量颇丰。如果南海南部的夏季海水表层在整个研究时间范围内能一直能提供适宜的温度条件的话，冰期时较深的温跃层以及1143站与陆地距离的缩短可能是粉红色G．ruber大量出现的主要原因。ODP 1143站和1146站的天文调谐氧同位素剖面为对比南海南、北之间古海洋环境的差异提供了精确的年代标尺．浮游有孔虫主要属种、温跃层和古生产力的对比结果显示，南海南、北的表层海水环境由210万年至120万年左右趋同，而在120万年之后分异逐渐增大。这个转折与气候变化由斜率周期转为偏心率周期的开始时间相吻合，因此可能反映东亚冬、夏季风长时间尺度上的相互作用对晚第四纪偏心率周期开始增强的响应。冰期-间冰期时间尺度上，南海的温跃层深度和古生产力在南、北形成了“跷跷板”式的变化，即冰期时南部的温跃层比北部深，生产力也相对较低，而间冰期时则反之。这可能是由于冰期和间冰期时东亚冬、夏季风对南海南、北影响的差异以及冰期时低的海平面导致南部水道变窄或关闭所造成的。更多还原

【Abstract】 Planktonic foraminifera （PF） in a total of 997 samples from ODP Site 1143 （9°21.72’N, 113°17.11’E, water depth 2,772 m） were studied to reveal the past -2,100 kyr paleoceanographical changes in the southern South China Sea （SCS）, with a resolution averaging -2 kyr. Glacial-interglacial fluctuations and long-term changes in carbonate dissolution and preservation, sea surface temperature （SST）, depth of thermocline （DOT）, paleoproductivity and predominant PF species as responding to the East Asian paleomonsoon and tropical climatic evolution were investigated. In addition, predominant PF species, DOT and paleoproductivity between Site 1143 and 1146 were compared to imply the differentiation of upper ocean water environments between the southern and northern SCS due to glacial-interglacial reversal of the East Asian winter and summer monsoons and sea level change.PF fragmentation and absolute abundance, percentage of resistant species （RSP%）, carbonate content and coarse fraction （＞63μm） were used to indicate carbonate dissolution and preservation. Peaks of carbonate dissolution occurred during interglacial to glacial transitions, while preservation spikes were mainly observed during glacial to interglacial transitions. Carbonate cycle at ODP Site 1143 was influenced by both dissolution and terrigenous dilution. All carbonate dissolution and preservation indices are strongly coherent with -δ¹⁸O over the eccentricity and obliquity bands. In general, maximal carbonate preservation leads and intensified dissolution lags minimal ice volume on these two orbital bands.FP-12E, SIMMAX-28 and ANN （Artificial Neural Network） techniques were employed to estimate paleo-SSTs based on PF assemblages and the results were evaluated. These estimates generally show higher SST values in glacials than interglacials, likely a bias by predominant species. Before other quantitative methods independent of faunal assemblages are developed for ODP Site 1143, the ratio of Globigerinoides sacculifer to Globigerinoides ruber was used in this study to provide the solution to qualitatively estimating SST variations. Cross-spectral and phase analyses of G. sacculifer/G, ruber and benthic foraminiferalδ¹⁸O indicated that maximal SSTs led ice volume minima (lowestδ¹⁸O) on the eccentricity, obliquity and 23-and 19-ka precession bands. Moreover, G. sacculifer/G. ruber ratio displayed significant half-precessional powers. This implies that tropical processes, rather than ice volume, have been playing an important role in temperature variations in the southern SCS.DOT and productivity were related to changes in the wind stress of the East Asian monsoon. DOT was indicated by mix-layer and thermocline dwelling species and calculated by transfer function based on faunal assemblages. The ratio of asyrnbiotic to symbiotic species was proved to be a good indicator of paleoproductivity. The southern SCS was characterized by deeper thermocline and lower productivity in glacials than interglacials. This indicates that intensified East Asian winter monsoon occurred during glacials and summer monsoon enhanced during interglacials. On a longer timescale, the thermocline depth and paleoproductivity underwent profound shifts at 1,650 ka and 850 ka, likely as a direct response to the stepwise evolution of the East Asian monsoon. Besides the dominance of the 41-ka obliquity cyclicity, half-precession periodicities were remarkably significant in variabilities of the thermodine depth and paleoproductivity, indicating that tropical climate factors including the East Asian monsoon played a key role in fluctuations of upper ocean structure in the southern SCS.G. ruber, G. sacculifer, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata and Globorotalia menardii dominated the faunal assemblage at ODP Site 1143. The relative abundance of G. ruber, G. sacculifer and N. dutertrei exhibited vague glacial-interglacial fluctuations, probably in response to a combination of carbonate dissolution, DOT, SST and productivity. On a long time scale, G. ruber mirrored N. dutertrei in displaying profound changes at 1,600 ka and 850 ka, but G. sacculifer changed little. The opposite change in G. ruber and N. dutertrei likely reflects a long-term change in thermocline and paleoproductivity. The long-term behavior of G. sacculifer may be due to its adapting flexibility to thermocline change.Two tropical carbonate-dissolution species, G. menardii and P. obliquiloculata, both favor shallow thermocline but displayed different responses to glacial-interglacial cycles in the southern SCS. More abundant G. menardii in interglacials than glacials was due to the shallow interglacial thermocline in the southern SCS. However, P. obliquilculata is reversely correlated withδ¹⁸O) profile with high abundance in glacials since the Mid-Pleistocene Revolution （MPR）. Investigation of its downcore variations at sites in western Pacific marginal seas indicated that the reverse correlation is unique to the southern SCS. Before the MPR, P. obliquiloculata was abundant in interglacials. High abundance of P. obliquiloculata during glacials after the MPR can be ascribed to increased regional seawater salinity, a connection of southern SCS waters to the western tropical Pacific or water conditions similar to the modern western tropical Pacific formed in the southern SCS.The pink morphotype of G. ruber has distinctive abundance in glacials and cool interglacial sub-stages, in contrast to records elsewhere. A deeper thermocline or the proximity of ODP Site 1143 to land during glacials is suggested to be responsible for the occurrence of large numbers of pink G. ruber, if the summer SST in the southern SCS provided an optimum temperature condition throughout the time interval.Orbitally tuned oxygen isotope strafigraphies from both Site 1143 and 1146 provided an accurate chronologic framework to compare paleoceanographic differences between the southern and northern SCS. The differences in dominant species, DOT and paleoproductivity indicated a profound differentiation of surface water environments between the two regions at～1,200 ka. This transition was considered to be a response in the long-term interaction between winter and summer monsoons to the progressive dominance of the eccentricity astronomical cycle in the late Quaternary. On the glacial-interglacial timescale, a see-saw like pattern was revealed in changes in DOT and associated paleoproductivity between the southern and northern SCS. During glacials, thermocline was deeper and productivity was lower in the south than in the north, and vice versa in interglacials. This is interpreted to be mainly due to differential glacial-interglacial impacts of winter and summer monsoons in the northern and southern SCS, as well as influence of glacial sea level lower-stands.更多还原