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

Abstract

We investigated molecular distributions and stable carbon isotopic compositions (delta C-13) of sedimentary n-alkanes (C-15-C-35) 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-C-27, n-C-29, and n-C-31. The delta C-13 signatures of n-C-27, n-C-29, and n-C-31 indicate a large contribution of C-3 gymnosperms as the main source of n-alkanes, with the values of -29.5 +/- 1.3 parts per thousand, -30.3 +/- 2.0 parts per thousand, and -30.0 +/- 1.7 parts per thousand, 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-C-28 and n-C-30 in this area have higher delta C-13 values (-26.2 +/- 1.5 parts per thousand and -26.5 +/- 1.9 parts per thousand, respectively) than the odd-carbon-numbered long-chain n-C-29 and n-C-31 (-28.4 +/- 2.7 parts per thousand and -28.4 +/- 2.4 parts per thousand, 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. (C) 2016 Elsevier Ltd. All rights reserved.