海洋生态与环境科学重点实验室知识库

西太平洋边缘海既有受人为活动影响强烈的近岸-近海海域，也有受人类活动影响相对较小、生态环境对气候变化响应灵敏的深海区域，作为地球海-陆-气圈相互作用最强烈的区域之一，其有机质沉降、埋藏和转化记录了过去生态环境演变的大量讯息，是有机质沉降、埋藏和转化的重要场所。研究从近岸到深海典型区域海洋生态环境演变特征对系统认识人类活动和气候变化与西太平洋边缘海生态环境演变的关系有重要意义。生物标志物具有可追溯的化学稳定性和特异性指示作用，能够有效示踪海洋沉积物中有机质来源、指示浮游植物生产力与群落结构演变等重要过程。本研究通过对西太平洋边缘海三个典型区域（胶州湾、长江口邻近海域和台湾东部黑潮主流径）表层和柱状沉积物中甾醇、正构烷烃和色素等生物标志物含量与组成进行研究，结合沉积物总有机碳（TOC）、总氮（TN）和稳定碳同位素（δ¹³C）等地球化学参数的变化分析，系统探讨从近岸到深海典型区域的生态环境演变过程及其影响因素，获得了如下主要结果和新的认识：

1. 基于沉积物特征甾醇分析和δ¹³C端元模型获取了胶州湾、长江口邻近海域和台湾东部黑潮主流径沉积物中有机质来源的海陆源比例。西太平洋边缘海三个典型海域沉积物中海源输入有机质（MOM）是主要来源，平均占比55~73%。近岸的胶州湾和长江口邻近海域沉积物中MOM的贡献量高于深海区的台湾东部黑潮主流径，可能与人类活动影响下近岸海域陆源输入巨量营养盐大幅增加对浮游植物生产力的促进作用有关。

对于受人类活动影响较大的近岸海域，基于特征甾醇分析和δ¹³C端元模型计算胶州湾中部柱状沉积物中MOM占比平均分别为70%和68%；长江口及其邻近海域表层沉积物中MOM占比平均分别为63%和73%；长江口邻近海域柱状沉积物中MOM占比平均分别61%和70%。对于受人类活动影响相对较小的台湾东部黑潮主流径海域，通过特征甾醇计算的MOM平均占沉积物中总有机质的55%，与此前通过δ¹³C模型计算的MOM平均占比55%的结果一致。基于甾醇和δ¹³C计算沉积物中MOM占比存在一定差异，可能与端元的选择及其来源的干扰因素有关，因此综合利用多参数方法更有利于准确判定沉积物中有机质来源。

西太平洋边缘海三个典型海域沉积物中正构烷烃总量（C₁₃~C₃₆）无明显差异，其分布模式均以双峰模式为主，表明沉积物中正构烷烃主要为海陆源混合，但在利用陆源与海源正构烷烃含量之比（ΣTALK/ΣMALK）和陆源与海源优势正构烷烃含量之比（TAR）指示陆源相对海源输入有机质变化时得出的结果与特征甾醇分析的结果存在差异，这可能与低碳数正构烷烃所受影响因素较多有关。低碳数正构烷烃优势指数（CPI_L）指示短链正构烷烃不具备明显的奇碳优势，因此可能受到微生物作用或石油烃污染。

2. 基于沉积物生物标志物甾醇和色素反演百年尺度胶州湾和长江口生态环境的动态演变过程可知，近百年来胶州湾和长江口邻近海域浮游植物生产力整体上随年代均呈增加趋势，且硅藻和甲藻类群对浮游植物生产力的贡献率逐渐增加。胶州湾生态环境演变受控于人类活动影响下周边农业化肥施用和污水排放造成的营养盐及其结构的变化；长江口邻近海域浮游植物演变除受控于人为活动输入的陆源营养盐，还与沿岸上升流营养盐的补充有关。

胶州湾C3站位柱状沉积物中浮游植物甾醇和色素含量的变化均表明近80年来胶州湾中部浮游植物生产力逐渐增加。诊断色素分析结果表明硅藻是胶州湾中部最主要的浮游植物类群（占比19~67%），其次为微型鞭毛藻（4~48%），甲藻和蓝藻对浮游植物生产力的贡献相对较低，分别为2~32%和0~39%。作为常暴发赤潮的浮游植物类群，硅藻和甲藻的相对贡献率随时间变化呈现升高的趋势，这一演变过程主要受控于人类活动的影响。

长江口及其邻近海域表层沉积物中浮游植物甾醇和色素的平面分布表明浮游植物生产力高值区主要位于长江口和浙江近岸海域，诊断色素分析的结果表明硅藻在研究区浮游植物类群中占据主导地位（平均占比66%），其次为微型鞭毛藻（平均占比22%），硅藻和蓝藻的贡献率较低，平均分别为7%和5%。硅藻在长江口和浙江近岸海域相对丰度较高，微型鞭毛藻的分布状况与硅藻相反，甲藻在上升流区相对丰度较高，蓝藻在江苏近岸相对较多，这一分布规律主要受长江冲淡水和沿岸上升流输入营养盐的综合作用影响。近30年来浙江近岸海域za1站位浮游植物生产力逐渐升高，硅藻和甲藻类群对浮游植物生产力的贡献率均呈现升高趋势，这与人为活动影响下陆源输入营养盐增多有关，同时气候变化可能引发沿岸上升流的增强，有助于底层富含硅酸盐水体的涌升，从而促进浮游植物尤其是硅藻的生长。

3. 基于沉积柱生物标志物甾醇重建了千年尺度西太平洋边缘海典型深海区-台湾东部黑潮主流区的生态环境演变规律。同近岸海湾和河口系统相似，台湾东部黑潮主流区的浮游植物生产力整体上随年代变化有所增加，但从近岸到深海海域人为活动对浮游植物演变的影响逐渐减弱而气候变化的影响逐渐突显。基于沉积柱中陆源与海源甾醇含量之比（Ter/Mar）、浮游植物甾醇含量和菜籽甾醇与甲藻甾醇含量比值（B/D）的变化明确识别出近千年来研究区的三个气候变化阶段，包括中世纪暖期（1150~1500年）、小冰期（1500~1800年）和现代暖期（1800年至今），整体随年代变化呈现陆源输入有机质增多、浮游植物生产力水平有所提升和硅藻竞争优势逐渐增强的趋势。

台湾东部深海区KET-1柱状沉积物中浮游植物甾醇含量呈现波动式升高，B/D比值自1500年以来明显升高，表明近千年来台湾东部黑潮主流径浮游植物生产力有所提升，同时硅藻相对甲藻的生长逐渐增加。台湾东部河流在向研究区输送陆源有机质的同时也会补充一定的营养盐，因此台湾东部地区降水量是影响浮游植物演变的重要因素，台湾地区的台风降水和季风降水主要受控于气候变化。在中世纪暖期（1150~1500年）台湾东部气候温暖干旱，陆源输入有机质和营养物质较少，因此该时期浮游植物生产力水平较低。小冰期（1500~1800年）台湾地区气候逐渐转向寒冷湿润的特征，季风降水和台风降水增多，有助于陆源营养物质的输送，因此在小冰期台湾东部黑潮主流径海域硅藻的竞争优势逐渐增强。现代暖期（1800年至今）以来台湾地区气候较为温暖湿润，同时西太平洋海平面升高增强了黑潮水动力，因而有助于台湾东部河流的输入，因此现代暖期以来浮游植物生产力水平有所提升。由于现代黑潮表层水体营养盐浓度较低，并且存在氮限制，该营养盐结构更有利于硅藻的生长，因此现代暖期以来台湾东部黑潮主流径海域硅藻的生长仍然占据主导地位。

Marginal seas of the western Pacific (MSWP) not only contain coastal zone greatly influenced by human activity, but also contain deep sea areas, where the ecological environments are less affected by human activity but sensitively responded to the climate change. As one of the strongest sea areas with air-sea-land interactions, MSWP also are the important space of organic matter (OM) settling, burying and transferring. Study on the evolution of typical sea areas from the coastal zone to ocean in MSWP is helpful for understanding the relationship of human activity, climate change and the evolution of marine ecological environment. Biomarkers have been effectively used to trace the sedimentary OM sources and to indicate the marine phytoplankton evolution owing to their chemical stability and specific sources. Based on the surface and core sediments of three typical sea areas in MSWP, including Jiaozhou Bay (JZB), Changjiang Estuary (CJE) and its coastal areas and the Kuroshio mainstream of east Taiwan (KM-ET), this study detected and analyzed the contents and compositions of sterols, n-alkanes and pigments combined with other geochemical parameters, such as the total organic matter (TOC), the total nitrogen (TN) and the stable carbon isotope (δ¹³C), for the purpose of systematic exploring the evolution of marine ecological environment from the coastal zone to ocean and discussing the main influence factors, with series of results and understandings as followed:

1. Based on the end-member models of sterols and δ¹³C, the relative proportions of marine organic matter (MOM) and terrestrial organic matter (TOM) in sediments of three study areas were calculated. MOMs were main OM sources in the three typical study areas, with average of 55~73% to the total sedimentary OMs. MOM proportions in the sediments of JZB and CJE and its coastal areas were far more than that of KM-ET, which was closely related that the increase of terrestrial nutrients from elevated human activity was conductive to the enhancement of marine primary productivity in the coastal zone.

For the coastal areas significantly affected by human activity, the average MOM proportions in the sediment core of the inner JZB were 70% and 68% calculated by end-member models of sterols and δ¹³C, respectively. And the average MOM proportions in the surface sediments of CJE and its coastal areas were 63% and 73% respectively. As for the KM-ET less affected by human activity, the average MOM proportion calculated by sterol end-member model was 55%, which was identical with the result of previous study based on δ¹³C model. The results calculated by two models have differences, which was possibly related to the choice of end members and other interferences, thus it was meaningful of combing multiple parameters for accurate distinction of OM sources.

As for n-alkanes, the total n-alkane (C₁₃~C₃₆) contents in sediments of three typical sea areas had no distinct difference. The characteristic compositions of n-alkanes mainly displayed dual-modal in three study areas, suggesting that sedimentary n-alkanes were mixed marine and terrestrial input. However, the results based on the ratio of terrestrial source to marine source n-alkane contents (ΣTALK/ΣMALK) and the ratio of terrestrial source to marine source preference n-alkane contents (TAR) were different from the results based on the analysis of sterols, this was possibly related to that low carbon number n-alkanes were influenced by many factors. The Low Carbon Preference Index (CPI_L) indicated that there was no obvious odd carbon preference in low carbon number n-alkanes, suggesting that they are possibly affected by the micro-biological degradation or the contamination of petroleum.

2. The dynamic change process of the marine phytoplankton evolution in JZB and CJE on century scale were reconstructed based on sedimentary biomarkers, sterols and pigments. Overall, the phytoplankton productivity increased with age during the past century, as well as the proportions of diatom and dinoflagellate. The ecological evolution in JZB was mainly related to that the increase of fertilizer usage and sewage discharge under the influence of human activity severely changed the nutrient concentrations and structures in JZB. The phytoplankton evolution in CJE and its coastal areas was not only influenced by the anthropogenic terrestrial nutrient input, but also influenced by the nutrient supplement from the coastal upwellings.

Variations of the phytoplankton sterol contents and sedimentary pigment contents in the sediment core C3 of JZB indicated the increased marine phytoplankton productivity during the past ~80 years. The results of diagnostic pigment analysis indicated that diatoms were dominant phytoplankton community in JZB (with the proportions of 19~67% to the total phytoplankton productivity), followed by nanoflagellates (4~48%), and the proportions of dinoflagellate and cyanobacteria were relatively low, with 2~32% and 0~39% respectively. As the main harmful algae, the proportions of diatom and dinoflagellate increased with age in JZB, which was mainly controlled by the effects of human activity.

The distributions of phytoplankton sterols and sedimentary pigments in the surface sediments of the CJE and its coastal areas suggested that the high phytoplankton productivity zone was located at the CJE and Zhejiang coastal areas. The analysis of diagnostic pigments indicated that diatoms dominated in CJE and its coastal areas, with the average proportion of 66.3%, followed by nanoflagellates, with the average proportion of 21.5%. The proportions of dinoflagellate and cyanobacteria were the lowest, with the average proportions of 6.7% and 5.5% respectively. The relative abundance of diatom was high in the CJE and the coastal areas of Zhejiang, and the distribution of nanoflagellate was on the opposite. The relative abundance of dinoflagellate was high in the upwelling areas, and cyanobacteria were relatively abundant in the coastal areas of Jiangsu. This distribution pattern mainly controlled by the combined effects of nutrient inputs of Changjiang Diluted Water and of coastal upwelling. As for the za1 station of Zhejiang coastal area, the marine phytoplankton productivity increased during the past ~ 30 years, as well as the proportions of diatoms and dinoflagellates. It was likely related to the increased anthropogenic nutrient input. Meanwhile, the enhanced coastal upwelling under the influence of climate change was conductive to the upwelling of silicate-rich water, which was benefit for the phytoplankton growth, especially for diatoms.

3. The millennial-scale ecological environmental evolution in KM-ET, as the typical deep-sea area of the MSWP, was reconstructed based on the biomarker of sterols in the sediment core KET-1. Similar with the coastal zone of gulf and estuary areas, the phytoplankton productivity increased overall. However, the effects of human activity to the phytoplankton evolution weakened from the coastal zone to ocean, while the effects of climate change enhanced. Based on the analysis of the ratio of terrestrial sterol content to marine sterol content (Ter/Mar), the phytoplankton sterol contents and the ratio of brassicasterol to dinosterol (B/D) in the sediment core KET-1, three climate change stages were recognized during the last millennium, including the Medieval Warm Period (MWP, 1150~1500 AD), the Little Ice Age (LIA, 1500~1800 AD) and the Current Warm Period (CWP, 1800 AD to present). On the whole, riverine TOM increased with age, as well as the marine phytoplankton productivity, and the competitive advantage of diatoms enhanced during the past millennium.

The phytoplankton sterol contents in the sediment core of KM-ET increased with fluctuation, and the B/D ratio obviously increased since 1500 AD, suggesting the increased marine phytoplankton productivity and enhanced competition of diatoms compared with dinoflagellates during the past millennium. The primary nutrient supplement was mainly derived from the eastern Taiwan rivers, thus the rainfall in eastern Taiwan made great influence on the nutrient level of KM-ET. The rainfall in Taiwan was mainly controlled by climate change of monsoon and typhoon, thus the changes of marine phytoplankton evolution and TOM could reflect the local climate change over the last millennium. During the MWP (1150~1500 AD), climate in Taiwan was relatively warm and dry, which was not benefit for the transport of TOM and terrestrial nutrients, corresponding to the relatively low marine phytoplankton productivity. During the LIA (1500~1800 AD), climate in Taiwan turned cold and wet, the monsoon rainfall and typhoon rainfall increased, which was benefit for the TOM and terrestrial nutrient input, corresponding to the relatively high primary productivity. During the CWP (1800AD to present), climate in Taiwan was relatively warm and wet, meanwhile the raised sea level in western Pacific strengthened the hydrodynamics of Kuroshio Current, which was benefit for the eastern Taiwan riverine input, thus the phytoplankton productivity was elevated since the CWP. Besides, according to the modern observations, the surface Kuroshio water was charactered by low nutrient concentration and nitrogen limitation, which was more conductive to the growth of diatoms. Therefore, the phytoplankton community was still dominated by diatoms since CWP in the KM-ET.

第1章 绪论... 1

1.1 气候变化和人类活动影响下的海洋生态环境演变.. 1

1.1.1 受人类活动影响严重的海湾... 2

1.1.2 受河流输入影响的河口... 3

1.1.3 受人类活动影响较小的深海区... 6

1.2 有机生物地球化学指标在反演海洋生态环境演变中的应用.. 7

1.2.1 甾醇类化合物... 8

1.2.2 烷烃类化合物... 10

1.2.3 色素类化合物... 12

1.3 本论文选题意义与主要研究内容.. 15

第2章 样品采集与研究方法... 17

2.1 研究区域背景特征.. 17

2.1.1 胶州湾水文气候特征... 17

2.1.2 长江口及其近岸海域水文及沉积特征... 18

2.1.3 台湾以东黑潮主流区水文气候特征... 19

2.2 样品采集.. 22

2.3 分析方法.. 23

2.3.1 定年分析... 23

2.3.2 有机碳、氮含量及稳定碳同位素... 23

2.3.3 正构烷烃和甾醇... 24

2.3.4 色素类化合物... 26

第3章 从近岸到深海的沉积物有机质来源解析... 28

3.1 胶州湾中部沉积物有机质来源.... 28

3.1.1 有机碳、氮元素与稳定碳同位素示踪有机质来源... 29

3.1.2 甾醇类化合物示踪有机质来源.... 32

3.1.3 正构烷烃示踪有机质来源... 35

3.2 长江口及其邻近海域沉积物有机质来源.... 39

3.2.1 有机碳、氮元素与稳定碳同位素示踪有机质来源... 39

3.2.2 甾醇类化合物示踪有机质来源..... 42

3.2.3 正构烷烃示踪有机质来源..... 48

3.3 台湾以东黑潮主流区沉积物有机质来源.... 53

3.3.1 甾醇类化合物示踪有机质来源.... 53

3.3.2 正构烷烃示踪有机质来源... 57

3.4 本章小结.. 59

第4章 从近岸到深海浮游植物生产力与群落结构演变过程解析... 61

4.1 近80年来胶州湾中部海域浮游植物生产力与群落结构演变过程... 61

4.1.1 甾醇类化合物指征浮游植物生产力与群落结构演变..... 62

4.1.2 色素类化合物指征浮游植物生产力与群落结构演变... 64

4.2 长江口及其邻近海域浮游植物生产力与群落结构演变过程解析.... 70

4.2.1 甾醇类化合物指征浮游植物生产力与群落结构演变..... 70

4.2.2 色素类化合物指征浮游植物生产力与群落结构演变..... 75

4.3 近千年来台湾以东黑潮主流区浮游植物生产力与群落结构演变过程.... 84

4.3.1 甾醇类化合物指征浮游植物生产力与群落结构演变..... 84

4.3.2 有机质来源与浮游植物群落结构演变过程对气候变化的响应... 90

4.4 本章小结.. 93

第5章 结语与创新... 95

5.1 结论.. 95

5.2 创新点.. 97

5.3 展望.. 97

参考文献... 98

致 谢... 116

作者简历及攻读学位期间发表的学术论文与研究成果... 118