Phytoplankton Biomarker Ratios In Suspended Particles From The Continental Shelf Of The East China Sea And Reconstruction Of The Ecosystem Structure For Mud Area In The Southwest Of Jizhou Island

As a new geochemical index, biomarkers are produced only by certain species of organism and have steady chemical properties. Multi-biomarkers of marine sediments can be used to reconstruct variations in phytoplanktonic ecosystem structure. This study reports phytoplankton biomarker ratios in suspended particles from the continental shelf region of the East China Sea and evaluates their potential as community structure proxies. In this study, the variations of phytoplanktonic productivity and community structure for core B3 are reconstructed by use of biomarkers during the last 8kyr as well.Among the 11 stations, alkenones were detected in one sample, indicating low content of haptophytes. The ratios of brassicasterol to dinosterol from different depth of the same station do not vary significantly, indicating that these ratios are not controlled by degradation processes in the water column, but they can be used to trace the variation of the diatom/dinoflagellate. The ratios varies from 1.1 to 36, revealing spatial trends with higher values away from the coast indicating more diatoms, generally in accord with phytoplank- ton distribution patterns obtained by other methods. Our study provides modern field results supporting the use of these biomarkers as proxies for community structure. It also suggests that this method could be used for community structure reconstruction for the ECS. Biomarkers of core B3 from mud area in the southwest of Jizhou Island are also studied. The SST varied about 5℃during the Holocene, and an obvious cold event happened at ca.4ka. It can be correlated with variations of solar isolation and regional ocean current. The total and individual primary productivity increased over the last 8kyr. It may be related with increased supply of nutrients induced by the enhanced winter monsoon, the strengthened cold eddy and upwelling at 4ka. In addition, the increasing trend of n-alkane contents also supports the increased terrigenous inputs which also enhanced the productivity for core B3. The ecosystem structure changed obviously during the last 8kyr. The relative abundance of haptophytes decreased, and the contributions of dinoflagellates increased. There were not obvious changes in the relative abundance of diatoms. These results indicate the supply of nutrients had varied significantly during the Holocene.