【作者】 胡建芳；

【导师】 彭平安；

【作者基本信息】 中国科学院广州地球化学研究所 ， 地球化学， 2001， 博士

【摘要】 在过去的十几年中，南海古海洋学研究取得了一系列的研究成果，研究工作主要集中在南海北部，南海南部则研究较少；研究内容中生物地球化学特别是分子有机地球化学比较欠缺，开展这方面的研究对了解热带海洋碳循环以及气候变化显得十分重要。 本论文选取位于南沙海区西太平洋“暖池”范围内的17962沉积物岩芯（7°11′N，112°5′E）为研究对象，进行了高分辨率采样。在多次试验的基础上，建立起了一套严格的适用于高分辨分子地层学研究的有机质分离与定量方法，并用以成功地分析了17962钻孔岩芯沉积物的有机质。 通过对314个沉积物样品的有机分析，检测出了正构烷烃、脂肪醇、脂肪酸、长链不饱和脂肪酮、C₃₀—C₃₂长链烷基二醇等有机化合物。在此基础上提取了相关的古海洋学指标如海洋表层古生产力等的变化。C₃₀长链烷基二醇的稳定碳同位素值在-30.17～—38.98‰之间，反映出其先质为水生生物——海洋黄绿藻Eustigmatophytes。计算C₃₀和C₃₂的相对比值获得二醇参数（diol indices），发现本柱状样二醇参数的变化指示了南海3万年来的古海洋及古气候变化：南海经历了从半封闭到开放的演变，Heinrich冷事件及在Heinrich事件之间出现了一系列的百年到千年尺度的气候事件，即D／O循环；全新世的Younger Dryas事件在二醇参数上都有明确的反映。由C₃₀烷基二醇和长链不饱和酮含量分别计算出的黄绿藻、颗石藻古生产力揭示出南沙海区末次冰期的古海洋环境及古气候是不稳定的，两类浮游藻类的生产力在冰期都出现了较大的波动：黄绿藻、颗石藻的生产力在末次冰期都比全新世高，特别是在H3时都出现了生产力增大的事件，这一方面是由于末次冰期东亚冬季风活动加强，本海区上升流增强；另一方面则是因此时陆源营养盐的输入增多，引起海洋生产力增高，而且对于本海区来说，后者可能是比较重要的。 对于陆源指标，如高碳数类脂物的古堆积速率，一方面反映了陆源物对南沙海区海洋沉积的贡献，另一方面揭示了造成末次冰期南沙海区陆源物质输入增高的古气候事件。高碳正烷烃、长链脂肪醇、长链脂肪酸的单体化合物稳定碳同位素δ¹³C值：-34.15～—28.61‰、-35.79～—26.56‰、-31.75～—27.12‰都显示了其陆源C3植物输入的特征。C3植物的发育表明末次冰期的普遍干旱化在这一地区并不存在。同时这些化合物的堆积速率在H3都出现了极大值，与水生生物来源的生物标志物的变化一致，反映出在南海海平面降低，粪它陆架出露背景下这一时期丰富的季风降雨导致河流洪水泛滥，从而引起南沙海区输入的陆源营养元素增多，黄绿藻、颗石藻海洋表层生产力的增高。 17962柱状样沉积物有机分于化合物记录的古气候事件同格陵兰 GRIP冰芯氧同位素记录的古气候事件具有良好的可对比性，反映了南海与高纬度地区的古气候变化存在遥相关，季风可能是它们相互联系的纽带。更多还原

【Abstract】 In the last two decades, remarkable success has been achieved in the researches of paleoceanography in the South China Sea. Most of the works are concentrated on northern South China Sea. Only a few studies have been done about southern South China Sea. The researches about bio-geochemistry, particularly molecular organic geochemistry are limited. However, the study of organic matter in sediments is important for researches of the carbon cycle and paleoclimate changes in the tropical ocean.314 Samples of core 17962(7 11 N, 11 5 ’ E), located in west Pacific "warm pool", Nansha area of the South China Sea. A precise quantitative method applicable to high-resolution molecular stratigraphy was established. The organic compounds in the sediments of core 17962 were analyzed qualitatively and quantitatively by this procedure.w-alkanes, n-alkanols, n-alkanoic acids, l,15-C3o-C32 diols and long chain alkenones have been identified in extracts of 314 samples. The 613C values (-38.98?0.17 %o) and carbon distribution show that the marine microalgae Eustigmatophyceae are potential source of the C^-Cn diols. The relative ratio of CM over Ca2 diols (C3o diols / [Cw diols + €32 diols]), defined as the diol index, serves as a good indicator for changes in paleoceanography and paleoclimate in southern South China during the last 30.0 ka. The diol index is high in the warm phase and low in the cold phase in southern South China Sea. It corresponds well with the cold events recorded in the sediments of the North Atlantic, such as YD, HI, H2 and H3. The centennial-to millennial-scale climate events such as D/O are also presented between Heinrichs. The productivity of Eustigmatophytes and coccolithophorid calculated by the concentrations of Cao diol and long-chain ketones, respectively, indicate that the paleoceanographic environment and paleoclimate were unstable in Nansha area during the last glacial. The productivity of the two algae fluctuated greatly and was higher during the glacial than that in Holocene. The productivity ofEustigmatophyceae and coccolithophorid maximized at H3, which one hand was caused by the strengthen of upwelling induced by winter monsoon. And the other hand was caused by an increased terrigenous nutrient supply from the Sunda Shelf. Possibly the later is the main reason.Terrigenous proxies, for example, the accumulation rates of higher molecular weight lipids showed that terrestrial input in Nansha area is higher in the last glacial than that in Holocene. The specific stable carbon isotope of terrigenous long-chain compounds, the w-alkanes ( 13C= -34.15- -28.61 %o), the ?alkanols ( 13C= -35.79--26.56 ), and the H-alkanol acids (613C= -31.75- -27.12) evidence that they are derived from higher plants of C3, which implies that the surrounding area of southern South China Sea was not drought during the last glacial. The accumulation rates of terrigenous long-chain compounds peaked at H3, paralleling those of the algae biomarkers, demonstrate that the enhancement of Eustigmatophceae and coccolithophorid productivity at H3 is caused by an increased terrigenous nutrient supply from the Sunda Shelf. This interpretation coincides with Sunda Shelf laid bare, the low sea level and river flood due to the abundant monsoon precipitation in southern South China Sea in the last glacial.The fluctuations of the organic molecular compound proxies in sediments of core 17962 were correlated well with that of the 818O in GRIP ice core during the glacial, indicating the paleoclimate and paleoenvironment of the South China Sea were teleconnected with those of high-latitude area possibly by the monsoon activities.更多还原