基于铅稳定同位素指纹的东海内陆架典型中小河流物源识别及定量重建

The information is well preserved in the mud wedge along the inner shelf of the East China Sea (ECS), as the good nature archive, on interaction between the land and ECS, evolution of the East Asian Winter Monsoon and temporal change in the intensity of human activities in the Yangtze River Basin and so on. On the base of accurate identification of sediment provenance of the mud wedge, these sediment records from the inner shelf of the ECS could be rightly deciphered. Previous studies focus on the contribution of the Yangtze River, as one of the largest rivers in the word, on its sediment provenance, but recent researches have indicated that these small rivers make considerable contribution on sediment provenance in the inner shelf of mud wedge. So, the study would choose the typical small rivers in the Zhejiang and Fujian Province (Oujiang and Minjiang River) and the Yangtze River as the end member. These sediment cores from the regions both influenced by these rivers would be chosen for the research.The concentration of major and trace elements, the isotopic ratios of lead in the acid insoluble phase of sediments from the Yangtze River, Oujiang River and Minjiang River, sediment cores would be analyzed and then chemical composition fingerprint of sediments of these rivers would be determined. The sediment source would be identified by using correspondence and correlation analysis and then their contribution is estimated on the base of mass balance calculation. Based on the reliable sedimentation rate of these cores, their temporal distribution during last century would be determined and the reasonable explanation would be offered. The study would help us better understand the source to sink process in the Eastern China shelf, formation of the mud wedge and provide fundamental scientific information for marine environmental protection.

东海内陆架泥质楔是获取东海陆海作用、东亚冬季风强度演化和长江流域人类活动变化等信息的良好自然档案。有效提取上述环境信息的必要环节是正确识别泥质楔的沉积物来源。以往的研究关注的重点是世界性大河—长江对泥质楔的贡献，但是近些年的研究表明中小河流对它的贡献不可忽视。因此，本研究选取浙闽沿岸典型中小河流（瓯江和闽江）和长江作为陆源沉积物作为端元，选取受中小河流和长江共同影响海域的沉积物岩心，测定河流和岩心沉积物酸不溶组分常微量元素和铅稳定同位素的组成，提取各个端元沉积物的指纹特征，对岩心沉积物来源进行识别和定量估算，结合岩心的年代标定，重建该区百年来中小河流来源沉积物贡献历史。该申请对深入理解中国东部陆架沉积物“源-汇”作用和东海内陆架泥质楔的形成等具有重要的研究意义，并为近海海洋环境保护提供科学参考。

项目组完成了有关样品的铅稳定同位素的测试，获得了河流端元（长江、瓯江和闽江）、浙闽泥质区表层样品和5根柱状样沉积物的铅稳定同位素的组成。同时，也测定了浙闽中小河流（椒江、鳌江、瓯江、闽江和木兰溪等河流）沉积物样品的粘土矿物组成。项目组建立了环渤海泥质区近80年的铅稳定同位素的沉积记录，发现环渤海地区铅来源在近半个世纪发生了显著的变化，以化石燃料（煤炭和含铅汽油）燃烧为主转变为以煤炭燃烧和有色金属冶炼为主。尽管在国外许多区域，如西欧、美国、东南亚等，已经发现了沉积物中铅含量明显下降，但是类似的趋势并未在中国东部近岸海域沉积物（黄海、东海内陆架和渤海）中发现，这可能归因于重工业的发展和煤炭消耗量的急剧增加。此外，项目组发现长江沉积物酸不溶组分的铅稳定同位素组成特征与典型浙闽中小河流（闽江和瓯江）具有显著的差异，这主要受流域内出露岩石类型不同的影响。同时，浙江典型中小河流（瓯江）感潮带内沉积物酸不溶态组分的铅稳定同位素组成特征与长江更为接近，显示了这些区域受长江来源物质的影响明显。粘土矿物的变化规律与铅稳定同位素相似，不过闽江以南的赶潮带内沉积物的粘土矿物的组成特征明显受长江的影响较小。同时，两端元混合的模型可以很好的解释浙闽泥质区南部部分区域沉积物的来源，其中靠近闽江的地区，受闽江来源的沉积物的影响越大。而柱状样同位素组成特征则显示，近百年来，东海内陆架沉积物来源并未发生明显变化。