长江口及邻近海域沉积物间隙水中溶解有机碳的循环过程及控制机制

大河影响下的陆架边缘海是河流输入和海洋自生有机碳的主要沉积汇，在全球碳循环中发挥着重要作用。沉积物间隙水中溶解有机碳（DOC）是沉积有机碳早期成岩过程的中间产物，其在河口与边缘海强的动力条件下会向外释放，对水体溶解碳库产生重要的贡献。间隙水中DOC来源多样、组成复杂、活性不一且受多种因素影响，但目前对其循环过程和控制机制的了解很少，制约了对边缘海碳循环的深入认识。本项目以长江口及邻近海域为研究对象，应用最近发展起来的超高分辨质谱获得沉积物间隙水中DOC的分子组成，结合同位素组成（δ13C和Δ14C）和其他间隙水溶质分析，阐明沉积物间隙水中DOC的来源、组成、年龄和活性的时空变化规律及不同类型DOC的产生、消耗和转化过程，从分子和同位素水平上揭示长江口及邻近海域沉积物间隙水中DOC的循环过程和控制机制，进而更深入地了解该区域沉积有机碳的再矿化作用，丰富和深化对边缘海碳源汇的认识。

River-dominated marginal seas (RiOMars) collectively receive and store vast amounts of organic carbon (OC) derived from both land and the ocean and are major centers of OC burial and oxidation, thereby playing a critical role in the global carbon cycle. Dissolved OC (DOC) in marine sediment pore waters is an important pool of intermediates produced and consumed during early diagenesis of organic matter in sediments, which can be released into overlying water during resuspension of sediments in RiOMars under highly dynamic conditions in these regions and contribute to the dissolved carbon pool in water columns. The porewater DOC is characterized by multiple sources, complex composition and different reactivity and is influenced by various biogeochemical and oceanographic processes but remains poorly understood, which hinder the deep understanding of carbon cycling processes in marginal seas. In this project, DOC contents and its carbon isotopic abundance (δ13C and ∆14C), molecular composition based on ultra-high-resolution mass spectrometry, three-dimensional fluorescence characteristics, dissolved free amino acids, dissolved inorganic carbon and redox sensitive elements in pore waters of sediments collected from the Changjiang Estuary and adjacent shelf, as well as OC and microbial community in solid sediments, combined with these parameters in time-series incubated sediments, will be analyzed to better constrain the spatial-temporal variations of the source, composition, age and reactivity of DOC, and the production, consumption and transformation processes of different types of DOC. Implementation of this project will help to reveal the DOC cycling and its controls in sediment pore waters of the Changjiang Estuary and adjacent shelf at the molecular and isotope levels, which will contribute to better understand the remineralization of sedimentary OC in this region, and enrich and deepen the knowledge of marginal seas as carbon source and sink.