The Geochemical Characteristics of the Fatty Acids in the Core Sediments in the Northern South Yellow Sea

The geochemistry of the fatty acids in the modern sediments in the Northern South Yellow Sea is still poorly studied, and studies on the geochemistry of the fatty acids in relatively long-core sediment samples are lacking. Thus, the fatty acids in the core sediments in the Northern South Yellow Sea were separated and identified to study their components and distribution characteristics, and the sources of organic matter and the early diagenetic evolution of the fatty acids in the sediments were discussed. The results show that saturated straight-chain fatty acids (methyl ester) have the highest content in the core sediments in the Northern South Yellow Sea, which account for 83.89% of the total fatty acids (methyl ester). nC_16:0 is dominant, accounting for 30.48% of the n-saturated fatty acids (methyl ester). Unsaturated fatty acids (methyl ester) account for 7.59% of the total fatty acids (methyl ester). Binary unsaturated fatty acids (methyl ester) can only be detected in some samples, which are low in content and dominated by C_18:2. Based on the components and distribution of the fatty acids (methyl ester) in the core sediments in the Northern South Yellow Sea, combined with the characteristics of other lipid biomarker compounds, the actual geological background, and previous research results, it is considered that the sources of organic matter in the core sediments are marine–terrestrial mixed materials, with terrestrial materials dominating. The fatty acids’ (methyl ester) CPI, the relative content of short-chain saturated fatty acids (methyl ester), and the unsaturated fatty acids (methyl ester) in the core sediments show non-obvious variation as the burial depth increases, reflecting that the fatty acids in the core sediments are strongly degraded at the early diagenetic stage, and this degradation is controlled by various complicated factors.