Comparisons Of Lipid Biomarkers In Surface Sediments And Suspended Particles From The North Yellow Sea And The Bohai Sea

Multi-biomarkers have been widely used to reconstruct phytoplankton productivity and community structure. However, there are few studies about multi-biomarkers in the North Yellow Sea and the Bohai Sea. In this paper, lipid biomarkers were measured to study their distributions in surface sediments and particles from the North Yellow Sea and the Bohai Sea. Analyzed biomarkers included brassicasterol, dinosterol, long-chain alkenones and long-chain n-alkanes. High contents of the phytoplankton biomarkers were observed in the surface sediments from the mud areas of the North Yellow Sea and the Bohai Sea, consistent with TOC distribution. Biomarker contents were normalized to TOC to eliminate the influences of grain size and sedimentation rate. High values of TOC normalized biomarker contents were found in the areas with high primary productivity. Additionally, the relative ratios of phytoplankton biomarkers were used to indicate the relative contributions of diatoms, dinoflagellates and haptophytes in the North Yellow Sea and the Bohai Sea. High contribution of diatoms was observed in coastal areas, where abundant silicate can favor diatoms growth. In contrast, high contribution of dinoflagellates was found in the middle of the studied area, attributed to nutrients competition between diatoms and dinoflagellates. In the middle of the North Yellow Sea, high contribution of haptophytes corresponded to the intrusion path of the Yellow Sea Warm Current. Seasonal distribution of brassicasterol and dinosterol in suspended particles from the North Yellow Sea and the Bohai Sea is consistent with previous phytoplankton investigation. However, the distributions of brassicasterol and dinosterol in particles are different from those in surface sediments, which is likely related to following factors:1) marine biomarkers in the particles are produced in short time such as one season, but marine biomarkers in the surface sediments reflect long time scale exported production; 2)marine biomarkers in the particles are from the surface water, while marine biomarkers in surface sediments come from phytoplankton production throughout the water column; 3) moreover, the transport of organic matter from the surface water to the sediment is affected by degradation and grain size. Therefore, the distribution of marine biomarkers in the particles collected during one season has not strong correlation with those in the surface sediments. Additionally, the source of organic matter in surface sediments and particles was evaluated. The results show that the long-chain n-alkanes in the particles have no obvious odd-even dominance, likely related to the contamination from petroleum hydrocarbons in surface water. Nevertheless, the long-chain n-alkanes in the surface sediments have obvious odd-even dominance, and the distribution of the long-chain n-alkanes is consistent with TOC distribution in the sediments. In order to eliminate the influences of grain size and sedimentation rate, TMBR index is used to indicate the relative contribution of terrestrial organic matter in the surface sediments. High TMBR values were found in the Yellow River Estuary and coastal areas, indicating high terrestrial input in these areas, which is consistent with the results of C/N,δ l3C and CaCO3 in the surface sediments.