海洋生态与环境科学重点实验室知识库

深入研究过去近千年来气候变化特征对准确预测未来的气候变化意义重大，西太平洋边缘海尤其是黑潮源区的环境演变对东亚气候有重要影响，因此该区域也是全球气候变化和全球碳循环研究的重点区域。本文以台湾东黑潮主流径上的柱状沉积物为研究对象，基于AMS¹⁴C定年结果，通过解析沉积物粒度、粘土矿物组合及其晶体学特征，揭示了台湾以东黑潮主流区的沉积特征、控制因素和物质来源问题；通过对沉积物中稀土元素组成特征和形态的系统分析，明确了台湾以东黑潮主流区沉积物中稀土元素的地球化学特征及其受控因素；通过解析沉积物中生源要素及同位素获取了海源碳变化特征，首次报道了该海区近千年来海洋初级生产力的变化。同时，基于各项指标所揭示的环境信息与其他代用资料进行对比，探讨了近千年来台湾以东黑潮主流区沉积特征对气候变化的响应。获得的主要认识和结果如下：

1、台湾以东黑潮主流区近千年来的平均沉积速率为34.44 cm/ka，低于冲绳海槽南部（约60 cm/ka）而高于开阔大洋（0.6~0.9 cm/ka），具有从陆架向深海过渡的特征。沉积物组成中以粉砂为主（83.53%~88.12%），其次为粘土质成分（11.79%~16.47%），几乎不含砂质成分。对粘土矿物的定量物源分析结果表明，台湾以东黑潮主流区沉积物为多物源混合的结果，亚洲大陆风尘输送是研究区粘土矿物的最重要物源，提供了研究区26%~72%的粘土矿物，台湾东部河流的输入占据次要地位，向研究区提供了11%~55%的粘土矿物，而吕宋岛弧物质的贡献最少，仅11%~26%。

2、台湾以东黑潮主流区沉积物的稀土元素基本受陆源物质控制，在沉积物迁移、搬运过程中受化学和生物作用影响较小，继承了源区的陆源属性。近千年来本研究区沉积物稀土元素特征受粒度效应影响较小，而与沉积物物质来源和沉积作用密切相关。同时，稀土元素的轻重稀土分布特征为本研究区沉积物三端元混合的理论提供了地球化学依据。

对台湾东黑潮主流区沉积物中稀土元素赋存状态的研究揭示了稀土元素在地球化学循环中的反应过程，也有效揭示了影响稀土元素分布特征的重要因素。研究区沉积物中的稀土元素主要以残渣态形式（84.38%）存在，其次为可还原态（10.80%），在可氧化态（2.51%）和酸提取态（2.31%）中含量很少。另外，La、Ce、Pr、Nd四种轻稀土元素具有明显的陆源属性，而其它稀土元素更易受到氧化还原环境的影响。在研究区沉积物稀土元素的四种赋存状态中，酸提取态、可还原态和可氧化态对重稀土元素相对富集，且表现出一定的铈负异常，而残渣态则对轻稀土元素相对富集，具有明显的铈正异常。这可能是因为酸提取态、可还原态和可氧化态受深海碳酸盐饱和深度、氧化还原环境和生物生产力的影响对重稀土具有优先吸附和络合作用。另外，残渣态优先吸附轻稀土元素而表现出铈正异常的特征，决定了研究区沉积物中稀土元素总量呈现铈正异常的特点。

3、台湾以东黑潮主流区沉积物中的有机质主要为海源输入，陆源输入占据次要地位。通过解析生源要素及其同位素所获得的海源碳含量可以用于指示近千年来台湾东黑潮主流区的初级生产力变化。在1152 AD~1400 AD左右研究区的海洋初级生产力有稳定增加的变化趋势，在1600 AD~1750 AD期间有所降低，进入19世纪以后海洋初级生产力先减小后增大。海洋初级生产力的变化与表层海水温度、亚洲大陆风尘输送的营养物质多少有关。另外，成岩作用和台湾东海底沉积物的再悬浮对研究区沉积物中有机质含量有较大影响。

4、对台湾以东黑潮主流区沉积特征和古生产力的研究结果与台湾及周边地区已有的研究成果有较好的对应关系，基于这一点我们识别出了近千年来研究区较为明显的三个气候变化阶段，即中世纪暖期、小冰期和现代暖期。1152 AD~1400 AD左右可能对应中世纪暖期，较高的海洋初级生产力与暖水种/冷水种有孔虫比值对应了该时期较高的表层海水温度，较高的（伊利石+绿泥石）/蒙脱石比值也指示了该时期较强的东亚冬季风。1400 AD~1800 AD左右可能对应我国小冰期，逐渐降低的暖水种/冷水种有孔虫比值、1600 AD~1750 AD期间降低的海洋初级生产力水平以及减弱的东亚季风强度都反映了该时期寒冷湿润的气候特征。进入19世纪以来研究区沉积物总体表现出波动较大的气候变化特征，尽管现代暖期和中世纪暖期都有气温增暖现象，但在东亚季风强度和降水量上却存在差异，这可能与气候变化的强迫因子不同有关。同时，近千年来研究区的沉积特征除受到长时间尺度的气候变化影响外，还会受海底地震、台风和暴雨等突发事件的影响。

It is vital importance to research the characteristics of climate change during the last millennium for precisely forecasting the future climate change. The environmental change of marginal sea of West Pacific, especially the source area of the Kuroshio Current is vital important to the East Asian climate change, thus is the key area of global climate change researches and global carbon cycle researches. A core sediment in the main stream of Kuroshio, east of Taiwan were adopted in this thesis. Based on the AMS¹⁴C dates, by analyzing the grain size, combination of the clay minerals and their crystallography features, we revealed the sedimentary characteristics, controlling factors and the provenance of the sediments of Kuroshio mainstream, east of Taiwan. The biogeochemistry features of rare earth element (REE) and its controlling factors in the research area were clear by analyzing the combination and form of REE in the sediments. It made use of total organic carbon (TOC) and carbon stable isotope compositions in organic matter (δ¹³C) of sediments to estimate the sea-derived carbon contents. And the change of marine primary productivity in the research area for the past millennium were discussed based on the above study for the first time. Meanwhile, by correlation with environmental information revealed by indictors of this research, and other proxy data researches, we discussed the response of sedimentary characteristics in Kuroshio mainstream, east of Taiwan to the climate change during the past millennium. The major understandings and results have been obtained as follows:

1. The average sedimentary rate of the sediments in the Kuroshio mainstream during the past millennium was about 34.44 cm/ka, which was lower than the southern Okinawa Trough (about 60 cm/ka), and was more than the open ocean (0.6~0.9 cm/ka), showing the features of transition from the continental shelf to the deep seas. The main component in the sediments of the research area was silt (83.53%~88.12%), the minor component was clay (11.79%~16.74%), it contained little sand in the sediments. It showed that the sediments in the Kuroshio mainstream came from several provenances, about 26%~72% of the clay minerals of sediments on this study came from the Asian continental dust, about 11%~55% of clay minerals came from rivers of eastern Taiwan, and about 11%~26% of clay minerals came from the Luzon Arc.

2. The REEs in the sediments in Kuroshio mainstream, east of Taiwan, were mainly controlled by terrigenous materials, and was less influenced by the chemical and biological effect during the process of migration of sediment. Meanwhile, the distribution features of HREE and LREE provided geochemical basis for the theory of three end members mixing. Besides, the REE features of the sediments in the research area during the past millennium were slightly influenced by grain-size effect, and was closely related to the provenance and sedimentation.

The research of the combined forms of REE in the sediments of Kuroshio mainstream revealed the reaction procedure of REE geochemical cycle and reflected as well the influence factors of the distribution features of REE as well. The REE in the sediments of the research area existed mainly by residual fractions (84.38%) and reducible forms (10.80%). The contents in the oxidizable forms (2.51%) and acid-soluble forms (2.31%) were low. Besides, La Ce Pr and Nd had the features of terrigenous source, other REEs were more likely to be influenced by the oxidation-deoxidation status. Among the four combined forms, acid-soluble, reducible and oxidizable forms had the features of relative HREE enrichment and negative Ce anomalies, the residual fractions had the features of relative LREE enrichment and positive Ce anomalies. This probably because that acid-soluble, reducible and oxidizable forms were influenced by the calcite compensation depth, oxidation-deoxidation status and biological productivity, thus had the prior to absorb and complex HREE. Besides, residual fractions were prior to absorb LREE and thus had the feature of positive Ce anomaly, it determined the feature of positive Ce anomaly in the total REE in the sediments of the research area.

3. The organic matter in the sediments of the Kuroshio mainstream was mainly marine autogenic and was minor terrigenous input. It made use of biogenic elements and their isotope compositions of the sediments to estimate the sea-derived carbon contents, which was effective to indicate the marine primary productivity in the Kuroshio mainstream during the past millennium. The marine primary productivity was increased stably during 1152 AD~1400 AD, and was decreased during 1600 AD~1750 AD, and decreased first and then increased since 1800 AD. The marine primary productivity was mainly related to the sea surface temperature and the nutrients from Asian continental dust. Besides, the organic matter in the sediments of the research area was influenced mainly by the diagenesis and the resuspension of the sediments in submarine of east of Taiwan.

4. There were good correlations between our research on the sedimentary features and paleoproductivity in the Kuroshio mainstream, east of Taiwan and those reported records in Taiwan and its adjacent areas, based of which we recognized three climate change stages, which were the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the Current Warm Period (CWP). 1152 AD~1400 AD might correspond to the MWP, relative high marine primary productivity and the ratio of warm-water to cool-water foraminifera might reflect the high sea surface temperature, high ratio of the contents of illite and chlorite to the contents of smectite reflected relative strong East Asian Winter Monsoon (EAWM). 1400 AD~1800 AD might correspond to the LIA. The lower ratio of warm-water to cool-water foraminifera, the lower marine primary productivity and the weaker EAWM reflected consistently the climate features of cool and humid. The sedimentary features showed fluctuated rapidly climate change features. Although there was common point during the CWP and MWP, with relative high temperature, there was differentiation during two periods in the intension of EAM and the precipitation. The reason caused the difference might lie in the different external forcing factors of climate change. Meanwhile, the sedimentary features during the past millennium were not only influenced by long-time scale climate change, but also some sudden events, submarine earthquake, typhoon and rainstorm for example.

目 录

摘 要 I

ABSTRACT IV

第一章 绪论 1

1.1 近千年来气候变化与海洋学沉积记录 1

1.2 西太平洋黑潮源区沉积特征及黑潮输入对东海沉积物的影响 3

1.2.1 西太平洋黑潮源区地质及水文状况 3

1.2.2 西太平洋黑潮源区沉积物矿物组成特征及其影响因素 6

1.2.3 西太平洋黑潮源区沉积物元素地球化学特征及其影响因素 10

1.2.4 黑潮输入对东海陆架沉积物的影响 16

1.3 本论文的选题意义及主要研究内容 17

1.4 研究区域背景与样品采集 18

1.4.1 台湾以东黑潮主流区海洋地质与气候特征 18

1.4.2 样品采集与研究方法 23

第二章 近千年来台湾东黑潮主流区沉积物来源与稀土元素变化特征 27

2.1 近千年来台湾东部黑潮主流区沉积特征 27

2.1.1 定年结果及沉积速率 27

2.1.2 沉积物粒度特征 28

2.2 基于粘土矿物分析的近千年来台湾东黑潮沉积物来源分析 29

2.2.1 粘土矿物组成及垂直变化特征 30

2.2.2 粘土矿物物源分析 32

2.3 台湾东黑潮沉积物稀土元素分布特征及赋存状态 36

2.3.1 稀土元素地球化学特征 36

2.3.2 稀土元素来源分析 43

2.3.3 稀土元素赋存状态 47

第三章 基于沉积物反演的近千年来台湾东黑潮主流区古生产力及气候变化 53

3.1 沉积物海源碳的识别与古生产力的关系 53

3.1.1 碳、氮与同位素垂直分布特征 53

3.1.2 海源碳的识别及其与古生产力的关系 55

3.2 古生产力变化对气候变化的响应 57

3.2.1 近千年来研究区初级生产力变化特征 57

3.2.2 近千年来研究区气候变化对比分析 58

3.3 粘土矿物组成对气候变化的响应 61

3.3.1 代用指标的意义 61

3.3.2 粘土矿物组合对气候变化的响应 62

3.3.3 台湾以东海域沉积事件记录 64

第四章 结论 66

参考文献 68

致 谢 76

作者简历及攻读学位期间发表的学术论文与研究成果 78