Several studies have shown that the basin-scale nutrient level has increased since 1990s in the Yellow Sea. In addition to the nutrient increase, the ratios of macronutrients have been altered as the inorganic nitrogen has increased disproportionately compared to other nutrients. However, few data exist that show an actual long-term increase in the phytoplankton biomass and productivity. Here we present merged chlorophyll data that substantiate a progressive eutrophication in response to the nutrient enrichment. We also compare the trend of the eutrophication in the eastern and western sides of the Yellow Sea ecosystem.ortionately compared to other nutrients. However, few data exist that show an actual long-term increase in the phytoplankton biomass and productivity. Here we present merged chlorophyll data that substantiate a progressive eutrophication in response to the nutrient enrichment. We also compare the trend of the eutrophication in the eastern and western sides of the Yellow Sea ecosystem.