The Distribution And Driver Of The Spatial-Temporal Variations Of Lipid Biomarkers In Surface Suspended Particles In The East China Sea And The Southern Yellow Sea

The East China Sea (ECS) and the Southern Yellow Sea (SYS), one of the biggest shelf seas in the world, are facing dramatic changes due to oceanic processes and anthropogenic activities. Despite the lack of detailed studies on the spatial and temporal variations of lipid biomarkers in surface suspended particles in the YS and ECS, these biomarkers have been increasingly used for both productivity and community structure reconstructions. Thus, validation of their applicability in modern aquatic ecosystems is needed.In this study, we collected surface particulate matters in the SYS and ECS from four seasons 2011-2012 to investigate the spatial and temporal distribution of phytoplankton lipid biomarkers (brassicasterol, dinosterol and alkenones). The aims of the study are to:(ⅰ) investigate the concentration and distribution of the three lipid biomarkers in surface suspended particles in different seasons in the ECS and SYS; (ⅱ) elucidate the driver of the spatial-temporal variations of lipid biomarkers; and (iii) further evaluate the use of lipid biomarker as an indication of primary production and phytoplankton community composition in the surface water in the ECS and SYS.In spring, high concentrations of brassicasterol and dinosterol were located in the northern and central SYS, while high C37 alkenones was detected at only seven out of 81 stations. In summer, the highest concentrations of brassicasterol and dinosterol were observed in the Changjiang River Estuary in the ECS, while high C37 alkenones concentration occurred in the northwest and central SYS. In autumn, the concentrations of brassicasterol and dinosterol had the maximum values in Haizhou Bay, south bank of Shandong peninsula and P section (southeast area offshore of Yangtze river esrtuary), while C37 alkenone was higher in southeast of SYS. In winter, the high values of brassicasterol and dinosterol were observed in Subei cost of SYS and P section (southeast area offshore of Yangtze river esrtuary), while high concentrations of C37 alkenone occurred in the southeast of ECS. To compare the results from four seasons, the total contents of the three biomarkers in summer is the higher than those in the other three seasons, followed by autumn, spring, and winter. Brassicasterol had the highest concentration among the three lipid biomarkers in all four seasons (2011-2012). In spring and summer, higher productivity associated with higher brassicasterol/dinosterol (B/D). In spring and autumn, brassicasterol/dinosterol (B/D) was related respectively to dissolved inorganic nitrogen/phosphate (DIN/P) and (Si/DIN) in certain areas. In summer, B/D value was related to phosphate limit suggesting that phytoplankton community structure may largely be attributed to algal competition for nutrients.Similar distribution pattern of the total amount of lipid biomarkers and pigments indicates that lipid biomarkers can be a new and useful tool for assessing phytoplankton primary productivity and community structure in the surface waters of the oceans.Our results indicate that turbidity and nutrients play an important role in regulating the concentration and distribution of phytoplankton lipid biomarkers in spring and summer, respectively. The driver of the concentration and distribution of phytoplankton lipid biomarkers in autumn was turbidity. In winter, the distribution of lipid biomarkers was mainly controlled by temperature and light, while sediment resuspension and nutrients from subsurface water of Kuroshio also play important roles in Subei shoal and in the southeast of ECS, respectively.