State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China
The National Science and Technology Major Project of the Ministry of Science and Technology of China under contract No. 2016YFC1402106; the National Natural Science Foundation of China under contract Nos 41376089, 41576083, 41976040, 41876127 and 42030402; the China Postdoctoral Science Foundation under contract No. 2020M671048.
The Subei Shoal is the largest sandy ridge in the southern Yellow Sea and important source for nutrient loading to the sea. Here, the nutrient fluxes in the Subei Shoal associated with eddy diffusion and submarine groundwater discharge (SGD) were assessed to understand their impacts on the nutrient budget in the Yellow Sea. Based on the analysis of 223Ra and 224Ra in the field observation, the offshore eddy diffusivity mixing coefficient and SGD were estimated to be 2.3×108 cm2/s and 2.6×109 m3/d (16 cm/d), respectively, in the Subei Shoal. Combined the significant offshore decreasing gradients of nutrient in seawater of the Subei Shoal, the spatially integrated nutrient outwelling fluxes to the Yellow Sea were 262−1 465 μmol/(m2·d) for DIN, 5.2−21 μmol/(m2·d) for DIP and 711−913 μmol/(m2·d) for DSi. Compared to the riverine input, atmospheric deposition and mariculture, nutrient outwelling from the Subei Shoal might play an important role in nutrient budget of the Yellow Sea. These nutrient fluxes could provide 4.1%−23% N and 1.3%−5.3% P requirements for the primary productivity, and the deviated DIN/DIP ratios have the potential to affect the growth of phytoplankton in the marine ecosystem of the Yellow Sea.
Figure 7. Nutrient outwelling fluxes from eddy diffusion and SGD-derived nutrient fluxes from the Subei Shoal to the Yellow Sea.
Figure 8. Fluxes of nutrients to the Yellow Sea derived by outwelling, riverine inputs, atmospheric deposition and mariculture. Gray lines indicate the average nutrient-supported primarily productivity in the Yellow Sea (Jin et al., 2013). DSi flux from mariculture was unavailable.