Contribution of petroleum-derived organic carbon to sedimentary organic carbon pool in the eastern Yellow Sea (the northwestern Pacific).

We investigated molecular distributions and stable carbon isotopic compositions (δ(13)C) of sedimentary n-alkanes (C15C35) in the riverbank and marine surface sediments to trace natural and anthropogenic organic carbon (OC) sources in the eastern Yellow Sea which is a river dominated marginal sea. Molecular distributions of n-alkanes are overall dominated by odd-carbon-numbered high molecular weight n-C27, n-C29, and n-C31. The δ(13)C signatures of n-C27, n-C29, and n-C31 indicate a large contribution of C3 gymnosperms as the main source of n-alkanes, with the values of -29.5 ± 1.3‰, -30.3 ± 2.0‰, and -30.0 ± 1.7‰, respectively. However, the contribution of thermally matured petroleum-derived OC to the sedimentary OC pool is also evident, especially in the southern part of the study area as shown by the low carbon preference index (CPI25-33, <1) and natural n-alkanes ratio (NAR, <-0.6) values. Notably, the even-carbon-numbered long-chain n-C28 and n-C30 in this area have higher δ(13)C values (-26.2 ± 1.5‰ and -26.5 ± 1.9‰, respectively) than the odd-carbon-numbered long-chain n-C29 and n-C31 (-28.4 ± 2.7‰ and -28.4 ± 2.4‰, respectively), confirming two different sources of long-chain n-alkanes. Hence, our results highlight a possible influence of petroleum-induced OC on benthic food webs in this ecosystem. However, the relative proportions of the natural and petroleum-derived OC sources are not calculated due to the lack of biogeochemical end-member data in the study area. Hence, more works are needed to constrain the end-member values of the organic material supplied from the rivers to the eastern Yellow Sea and thus to better understand the source and depositional process of sedimentary OC in the eastern Yellow Sea.