Summertime nutrient transports in the coastal areas of the Western Northern Yellow Sea

Abstract

The summertime nutrient transports in the western Northern Yellow Sea (NYS) have not been well understood due to regional complex physical-biological processes. A coupled model was developed to investigate the summertime nutrient transports in the western NYS. Based on a suite of quantitative skill metrics, the model performance was comprehensively evaluated by comparing the simulated results to a collection of observational data in 2019. The model results were capable of reproducing the observed hydrographical conditions and nutrient distributions in different seasons. In the summer, the coastal areas in the east of Liaodong Peninsula (Zone1) and north of Shandong Peninsula (Zone2) both lost nutrients through cross-boundary nutrient transports for Dissolved Inorganic Nitrogen (DIN) and Dissolved Inorganic Phosphate (DIP). Changes in the surface wind altered the regional circulation and consequently caused variations in nutrient transports for the two zones. Increase in the velocities of southerly wind led to more nutrient losses in Zone1 and less nutrient losses in Zone2. Further sensitivity analysis suggested that the Yalu River was not the dominating factor influencing the nutrient budget of Zone1, and oceanic nutrients contributed around 70 % of the DIN and 99 % of the DIP transported into Zone1. The outflow from Bohai Sea (BS) to NYS dominated the nutrient budget of Zone2. Among the nutrients from the BS, 94.76 % of the DIP were from internal nutrient pool and 3.03 % were from newly input riverine nutrients, those ratios for DIN were 78.79 % and 19.30 %. The Yellow River and Yalu River discharges modulated the regional circulations introducing moderate variations to the nutrient budgets of Zone1 and Zone2.