南海北部和海南岛附近海域表层沉积物中有机质的分布和降解状态的差异

The South China Sea receives sediments from multiple sources of adjacent lands and islands and hosts rich in fossil fuel resources. To understand organic carbon (OC) origination, transportation, and degradation in water and sediment, surface sediments were sampled in two maritime regions, i.e., the northern South China Sea along Zhujiang (Pearl) River delta (ZJ) and waters to the east of Hainan Island (HN), two major marine oil-gas productive fields of China. Sedimentological (grain size, specific surface area (SSA)) and geochemical (OC%, δ ¹³ C-OC and n-alkanes, fatty acids) studies were performed. Samples were mostly fine-grained sand-silt sediments and showed a tendency of fining away from land. Parameters of OC% (0.15-1.18), δ ¹³ C (-23.05‰- -21.24‰) were determined, and molecular biomarkers (n-alkane carbon preference index and types of fatty acids) were measured. Correlation between SSA and OC% was not significant. Correlation between OC load (OC/SSA) and δ ¹³ C in HN samples was positive, showing good transition from terrestrial to marine origination from land to ocean, which is normal; however, this phenomenon was not observed in the ZJ samples. We believe that the difference shall be resulted from selective adsorption by clay minerals different in species and fraction between the two sets of samples. ZJ samples are affected by multiple sources from South China continent, Taiwan and Luzon Islands, while that of HN from nearby single Hainan Island.