@@ The spatial and temporal distributions of POC, as well as fluxes of bulk particulate organic carbon (POC) and size-fractionated (1-10, 10-50, 50-150, and > 150 nm) POC were measured during the summer 2007 and winter of 2008 in the East China Sea (ECS) (Fig. 1) to better understand the importance of lateral organic carbon export from marginal seas to the open ocean. The distribution of POC in surface waters of the ECS exhibits a strong seaward variation, with high POC concentrations (>400 ug L-1) in the inner shelf and low POC inventory in the outer shelf (50-100 μ.g L-1) during the summer (Fig. 2A). A strong lateral surface POC concentration gradient across the shelf (Stations 19 to 24) was found in summer with a high vertical POC concentration band appearing from the surface to approximately 20 m depth in the inner and middle shelves and gradually decreasing to the outer shelf (Fig. 2B). During the winter, surface POC concentrations were only one third of summer values and most of the POC appeared along the coast (Fig. 2C). The vertical seaward POC concentration gradient (Stations 19-24) was not pronounced during the winter (Fig. 2D), but elevated POC concentrations were observed near the sea floor at Stations 20-22, close to the inner and middle shelf. The results reflect that the inner and middle shelves close to the Changjiang River mouth is an important source of organic carbon in summer.