Marine dissolved organic matter (DOM) plays a crucial role in the global carbon cycle. Carbon cycling in marginal seas is highly complex because it is regulated by numerous source-sink processes. Here, we investigated the spatial variability of the bulk, optical properties, and molecular compositions of DOM in the Yellow Sea (YS) and East China Sea (ECS) and its influencing factors. The DOM in the study area was dominated by protein-like component, highly unsaturated and phenolic compounds, and CHO formulas. The dissolved organic carbon (DOC), chromophoric DOM, and fluorescent DOM decreased with increasing salinity and depth, and within the three regions they were ordered: northern YS > southern YS > ECS. Due to the greater influence of anthropogenic inputs and phytoplankton production in the YS, it contained significantly more heteroatomic compounds and labile compounds (aliphatic, peptide-like, and sugar-like compounds) than the ECS. Moreover, unlike in the open ocean, none of the compound categories exhibited significant variability with depth in these shelf seas. Redundancy analysis suggested that dilution was a main factor determining the spatial distributions of DOM. The polycyclic aromatics and polyphenolics decreased in the seaward direction, but they were still present offshore, indicating they contributed to the open-ocean carbon pool. Anthropogenic inputs obscured potential correlations among the labile compounds and salinity and phytoplankton production. In addition, compounds with high molecular weights and low unsaturated CC functionalities were preserved during the carbon cycle, due to their recalcitrant nature. By providing optical and molecular data, this study helps to better understand the biogeochemical cycling of DOM in marginal seas.

海洋溶解有机物（DOM）在全球碳循环中发挥着至关重要的作用。边缘海的碳循环非常复杂，因为它受到众多源汇过程的调节。在这里，我们研究了黄海（YS）和东海（ECS）中DOM的体积、光学性质和分子组成的空间变异性及其影响因素。研究区的DOM以类蛋白质成分、高度不饱和和酚类化合物以及CHO分子式为主。溶解有机碳（DOC）、发色DOM和荧光DOM随着盐度和深度的增加而降低，并且在三个区域内它们的顺序为：北部YS>南部YS>ECS。由于YS中人为输入和浮游植物生产的影响更大，它比ECS含有更多的杂原子化合物和不稳定化合物（脂肪族、肽类和糖类化合物）。此外，与公海不同，这些陆架海中没有任何化合物类别随深度而表现出显着的变化。冗余分析表明稀释度是决定DOM空间分布的主要因素。多环芳烃和多酚类化合物在向海方向减少，但它们仍然存在于近海，表明它们对公海碳库做出了贡献。人为输入掩盖了不稳定化合物与盐度和浮游植物产量之间的潜在相关性。此外，具有高分子量和低不饱和C C 官能团的化合物由于其顽强的性质而在碳循环过程中得以保留。通过提供光学和分子数据，这项研究有助于更好地了解边缘海 DOM 的生物地球化学循环。