Reconstruction of phytoplankton productivity and community structure in the South Yellow Sea

The sedimentary environment and ecological system in the South Yellow Sea(SYS) changed dramatically due to sea level change caused by glacial-interglacial cycles. The authors report the use of marine biomarkers(brassicasterol, dinosterol and C37 alkenones) and terrigenous biomarkers(C28+C30+C32 nalkanols) in core DLC70-3 from the SYS to reconstruct the variation in the phytoplankton productivity and community structure and possible mechanisms during the middle Pleistocene. The results show that the primary productivity and that of single algae presented a consistent trend for the whole core during the middle Pleistocene, which was high during interglacial periods and low during glacial periods, with the highest being in marine isotope stage(MIS) 5–9 and MIS 19–21. The main reason is that the Yellow Sea Warm Current(YSWC) carried much of high temperature, high salinity water into the SYS, causing upwelling and vertical mixing and stirring, which increased the nutrient supply in the photosynthetic layer.The phytoplankton community structure mainly showed an increase in the relative content of haptophytes in MIS 5–9 and MIS 19–21, while the relative content of diatoms and dinoflagellates decreased; there was no evidence for a haptophyte content in other stages. The results reveal a shift from a coccolitho-phoriddominated community during MIS 5 –9 and MIS 19 –21 to a diatom-dominated community during the other stages, mainly as a result of surface salinity variation, attributed to the invasion of the YSWC during high sea level periods.