【作者】 胡邦琦；

【导师】 杨作升；

【作者基本信息】 中国海洋大学 ， 海洋地质学， 2010， 博士

【摘要】 中国东部陆架海(渤海、黄海和东海)是世界上最宽阔的陆架海之一。长江和黄河输入的巨量泥沙是其主要的物质来源,对本海区的物质通量、陆架泥质沉积体的形成以及海洋生态环境有着重大的影响。确定长江和黄河物质的可靠识别指标,对于确定两种物源在中国东部陆架海区的时空分布,了解长江和黄河物质的“源-汇”作用、阐述陆架海区物质通量和认识东部陆架海区的演化过程等有着重要的科学意义。近年来,长江、黄河物源识别工作已经取得巨大的进展,但迄今为止在长江和黄河物质可能的物源混合区进行长江与黄河物质的准确识别还存在许多不确定性。同时,中国东部陆架海区泥质沉积体中蕴藏着全新世以来丰富的古环境信息,其变化受到大陆、海洋两方面环境变化的影响。这些泥质沉积体中的沉积物和石英敏感粒级、磁性、地球化学以及UK37-古水温等参数已被广泛用于东亚季风等环境变化的替代指标,取得了一系列成果,但目前在东部陆架海区关于东亚冬季风等环境因素的高分辨率长期记录比较缺乏。黄海暖流作为现代黄、东海环流体系的重要组成部分,受到了广泛关注,但目前大多数研究主要报道了其形成年代,对其形成以后的可能变化未进行讨论。本文以国家自然科学基金重点项目“末次冰消期以来东部陆架泥质区海洋环境演化的地质记录”和科技部国家重点基础研究发展计划(973计划)项目“我国陆架海生态环境演变过程、机制及未来变化趋势预测”为依托,研究了长江、黄河代表性表层样品23个,泥质区表层样品近150个、济州岛西南泥质区B3孔和南黄海中部泥质区的ZY-1、ZY-2、ZY-3孔4根柱样。利用沉积物粒度测试、X-衍射矿物分析、XRF地球化学分析、UK37-古水温测试、AMS 14C测年等多种分析手段,对中国东部陆架海区泥质区的物源识别和古环境记录进行了研究,得到以下几点结论：1.长江与黄河入海沉积物不同粒级中的矿物组合中,方解石与白云石含量的比例在细粒级部分(<16μm)差异最大,是长江与黄河流域风化程度和沉积物物质源区不同的集中体现。同时白云石不是生源物质,因此,在东部陆架海区沉积物中,可以采用<16μm粒级区间的方解石和白云石含量比值的差异,作为识别长江与黄河物源的可靠指标。2.利用<16μm粒级中的方解石和白云石比值差异对各泥质区表层沉积物中长江与黄河物源识别取得了很好的效果,尤其在两者混合区域。结果表明,黄河物质的影响在整个东部陆架海区泥质区中均有反映,但在渤海和北黄海海域,主要是现代黄河物质的供应,而在35°N以南的黄河物质主要来自苏北老黄河口再悬浮物质。长江物质分布范围比较小,主要集中在东海内陆架和济州岛西南泥质区,最南界不超过26°N,最北界不超过35°N。长江和黄河物质的扩散模式与中国东部陆架海的海洋动力条件密切相关。3.利用济州岛西南泥质区的B3孔沉积物<16μm粒级部分的方解石和白云石含量比例差异,揭示了全新世以来长江、黄河物质对此海区物源贡献的变化历史。结果表明,黄河物质分别在6.7～4.1和0.8～0 ka B.P期间对此海区有所贡献,可能显示了黄河在苏北入海的变迁史,与气候变化和人类活动密切相关。长江物质在6.0 ka B.P以来对此海区均有贡献,与全新世以来长江三角洲从堆积转变为进积的时间一致。B3孔的物源、粒度及沉积速率的变化,与海洋环境及长江与黄河物质供应量的变化历史有较好的对应关系。4.利用南黄海中部泥质区的3根柱样(ZY-1、ZY-2、ZY-3孔)的沉积物粒度和地球化学指标,研究了中全新世以来东亚冬季风的演化历史。结果表明,近7200年来东亚冬季风可大致划分为三个阶段,分别为7.2～4.2 ka B.P的东亚冬季风强盛期、4.2～1.8 ka B.P的东亚冬季风的稳定期和1.8～0 ka B.P的东亚冬季风转换期。轨道驱动的太阳辐射量(Solar insolation)变化的季节性差异使得中全新世以来东亚冬、夏季风在整体上呈同步减弱趋势,而太阳活动(Solar irradiance)在十年、百年尺度上使得东亚冬、夏季风反相变化。5.在6.2 ka B.P以来,南黄海中部ZY-2孔的海水表层温度(SST)的几次千年尺度降温事件与黑潮减弱事件和北大西洋浮冰(IRD)事件一一对应,表明低纬度边缘海区与高纬度地区的气候变化是同步发生的,有可能是对同一驱动力(Solar irradiance)的响应。通过多个钻孔海水表层温度之间比较,表明黄海暖流“前弱后强”,发现了10次黄海暖流减弱事件。黄海暖流的长期变化和短期的减弱事件与黑潮和西太平洋暖池区的SST变化基本一致,表明黑潮本身的强弱是影响黄海暖流的主要因子,而其他因素(如东亚冬季风)只在某些阶段会对黄海暖流产生显著的影响。更多还原

【Abstract】 The East China Seas (ECSs), consisted of the Bohai Sea, Yellow Sea and East China Sea, is one of the largest continental marginal seas in the world. Two large rivers (Huanghe and Changjiang) annually delivered more than 1.5 billion tons of sediments to the ECSs. These huge amounts of sediments are the primary terrigenous sediment sources of these epicontinental seas, and hence have immense impacts on the sedimentary, aquatic and ecological systems, as well as the geochemical cycles in these epicontinental seas. Therefore discriminating the provenances of the sediments is critical not only for understanding the temporal and spatial dispersal pattern of the sediments from the Changjiang and Huanghe, but also for deciphering and reconstructing paleoenvironmental changes archived in the sediment deposits. In recent years, great advances in discriminating the Changjiang and Huanghe sediments have been reached; however, there is also considerable uncertainty to distinguish them in the mixed areas. In addition, the mud depositional areas of ECSs archived abundant paleoenvironment information, which reflected both of the changes in the continent and ocean. Multi-proxies (bulk sediment and Quartz grain size, Magnetic properties, pollen, geochemical data, Alkenone-derived sea surface temperature) have been used to study the paleoclimate history archived in these mud deposits. However, there is little consensus about the long-term and high resolution records of the East Asia Winter Monsoon and the Yellow Sea Warm Current.A total of 23 samples collected from the Huanghe (12) and Changjiang (11) Estuary are separated into seven particle-size fractions (<2μm,2-4μm,4-8μm, 8-16μm,16-32μm,32-63μm,63-125μm). These sub-samples are analyzed by X-ray diffraction (XRD) to characterize its mineral assembles. The results show that the mineral assembles of the Huanghe and Changjiang sub-samples are much different with each other. Particularly, the carbonate minerals (calcite and dolomite) in the <16μm particle-size fractions exhibit significant discrepancy between the Huanghe and Changjiang samples, the calcite is the dominant carbonate minerals in the Huanghe sub-samples in<16μm fractions whereas the dolomite became more enrichment in the Changjiang sub-samples (<16μm). This discrepancy (Calcite/Dolomite ratio) is the result of the different chemical weathering intensity and sediment source within these two river basins. Therefore, it can be used as a reliable and simple proxy to distinguish the Huanghe and Changjiang sediments.The discrepancy of Calcite/Dolomite ratio in<16μm particle-size fractions is applied to identify the sediment provenance of 150 samples collected from the mud depositional area of ECSs. Results show that this proxy can easily distinguish the Huanghe and Changjiang sediment provenance in the mud area of ECSs, especially in the areas where the Huanghe and Changjiang sediments mixed. The Huanghe sediments can be found in almost all of the mud depositional areas whereas the Changjiang sediments are mostly constrained in the inner shelf and the Southwestern Cheju Island Mud (SWCIM).This proxy is also used to identify the Huanghe and Changjiang sediment provenance in the core-B3 (located in the SWCIM) during the Holocene. Results show that the Changjiang sediments have an effect on the SWCIM until 6.0 ka B.P., which consistent with the transition of the Changjiang Delta from the accumulation to progradation in 6.0 ka B.P.. Moreover, the contribution of the Huanghe sediments to the SWCIM only existed in two periods (6.8-4.1 and 0.8-0 ka B.P.), which likely revealed the history shift of the lower Huanghe in the Subei Plain. The evolvement history of sediment provenance in this area largely depend on the formation of marine current system, as well as the changes in the Huanghe and Changjiang sediment supplies, which related to the delta evolution and channel shifting.Three cores (ZY-1, ZY-2 and ZY-3) are retrieved from the central Yellow Sea mud (CYSM). AMS 14C dating, Grain-size and XRF-geochemical data for these cores are used to reconstruct the history of the East Asian Winter Monsoon (EAWM) since the mid-Holocene. Results show that these data provide a continuous history of the EAWM over the past 7200 years, and the EAWM can be divided into three periods:strong and highly fluctuation during 7.2～4.2 ka B.P.; moderate and relatively stable during 4.2～1.8 ka B.P. and weakened during 1.8-0 ka B.P.. The evolution history of EAWM broadly follows the orbital-derived winter insolation with a similar long-term step-decreased trend as the East Asian Summer Monsoon (EASM); however, an anti-relationship existed between them in centennial-scale, mostly likely caused by solar activity.Alkenone-derived sea surface temperature (UK37-SST) at Core-ZY2 varied largely over the past 6200 years, the UK37-SST of Core-ZY2 is relative low with three abrupt cooler events (5.0～5.4,3.8～4.0 and 3.0z 2.4 ka B.P.) during 6.2-2.0 ka B.P.; since 2.0 ka B.P., the UK37-SST of Core-ZY2 increased largely and relatively stable. The millennial-scale cooler events in Core-ZY2 are consistent with the Kuroshio current decreased events and the North Atlantic ice-drift events (Bond events). This implies the climate change in the low-latitude continental marginal seas is synchronized with the high-latitude areas, likely derived by the same driving force (e.g. solar irradiance).The sea surface temperature differences between several cores are used to reflect the intensity of the Yellow Sea Warm Current (YSWC). Results show that the intensity of YSWC in 6.2-2.0 ka B.P. is weaker than the later period (2.0～0 ka B.P.), with ten centennial-scale YSWC weaker events. The long-term trend and centennial-scale weaker events of the YSWC are consistent with the changes in UK37-SST of the Core MD05-2908 (located at Southern Okinawa Trough) and Mg/Ca-SST of the Core MD 81 (located at Western Pacific Warm-Pool). This suggests that the intensity of KC-self is the dominant factor controlling the variation of YSWC. The reconstructed intensity of TWC and KE is consistent with the previous studies.更多还原