We investigated the source, composition and reactivity of sedimentary organic carbon (OC) in a river-dominated continental marginal sea, the eastern Yellow Sea. A multi-proxy approach was applied to riverbank sediments and marine surface sediments, combining bulk and molecular organic parameters. The sedimentary OC in the marine surface sediments appears to have a predominantly marine origin with minor contribution of continental (i.e. soil- and lake/river-derived) OC. However, the D14C values were depleted, indicating that about 18-33% of ancient OC, potentially derived from erosion of sedimentary bedrocks might be added to the sedimentary OC pool. Accordingly, our results highlight
an important contribution of ancient OC in the eastern Yellow Sea. Nonetheless, more work is needed to better constrain the source, composition, and age of the organic material supplied to the eastern Yellow Sea, given the lack of biogeochemical data from the Korean rivers.