Distribution Of Lipids Biomarkers In Surface Sediments Of The East China Sea And The Yellow Sea And Paleoecological Reconstruction

Multi-biomarkers have been applied for the reconstruction of phytoplankton productivity and community structure. Their ratios can be used for community structure reconstruction. However there is not sufficient evidence to verify this method, especially in the marginal seas of the West Pacific. In this paper, the distributions of biomarkers in surface sediments of the East China Sea and the Yellow Sea were studied to further validate the use of biomarkers in the studied area. And we also carries out the analysis of biomarkers in core drilled from the East China Sea and the Yellow Sea, and discuss the variations of biomarker-based records for the past 200y: sea surface temperature (SST), marine productivity and community structure.1. The distribution of biomarkers in surface sedimentsThe results indicate the contents of biomarkers (C37alkenones, brassicasterol and dinosterol) of the East China Sea ranged from 357 to 3115ng/g. The contents biomarkers of the Yellow Sea varied between 2898 and 6714ng/g .The results show that total phytoplankton biomarker contents decrease away from the coast, consistent with results from modern water column phytoplankton surveys. And the varieties are caused by higher productivity brought from the terrestrial input. So the contents of biomarkers from sediments can be used for semi-quantitative reconstruction of paleoproductivity.The biomarker ratio can be used as the proxies of phytoplankton community structure, and the biomarkers ratio shows that the relative diatom contribution decreased away from the Changjiang River mouth, but in the southern part of the East China Sea, the relative diatom contribution increased away from the coast. Coccolithophorid contribution was minor, but reveals a trend of increases with depth. These biomarker-based community structure trends are in agreement with field survey result, but the absolute values by the two methods differ.Compared with modern mean annual temperature, theU₃₇^K'-SST is higher in the East China Sea and the Yellow Sea. TheU₃₇^K'-SST in the East China Sea is similar to the mean temperature in summer, but U₃₇^K'-SST in the Yellow Sea accords with the mean temperature in autumn. These differences may be correlated with the species of coccolithforid and the seasonal variety of productivity and the calibration of U₃₇^K'-SST equation.2 Paleoecology Reconstruction of the East China Sea and the Yellow SeaThe U₃₇^K'-SST in the Yellow sea varied from 13.5 to 17.5℃over the last 210y, and the mean value was 15.4℃. The lowest SST (13.5) appeared at 104y before present, and then SST increased rapidly.Marine phytoplankton productivity in the Yellow Sea reveals a increasing trend which is similar to the trend of the contents of alcohols indicating terrestrial input during the past 200y,. The changes of productivity in the Yellow Sea could be controlled by winter monsoon. Similarly, the productivity in the East China Sea increased over the last 130y. The productivity changes in the East China Sea probably relates to human activity.The reconstructed phytoplankton community structure shows obvious variations in the Yellow Sea. The contributions of coccolithforids decreased, and the contributions of dinoflagellates increased, and the relative abundances of diatoms varied at low values from 210 to 100y before present. During the last 100y, the ratios of coccolithforids were low, the contributions of dinoflagellates decreased rapid, and that of diatom increased. Over the last 130y, the biomarker ratios show that the relative abundances of diatoms and coccolithforids decreased and that of dinoflagellates increased. Different community changes in the two marginal seas are ascribed to the different effects of climate change and human activity on them.