Intra- and inter-seasonal variations in the hydrological characteristics and nutrient conditions in the southwestern Yellow Sea during spring to summer

Abstract

Based on field survey in the southwestern Yellow Sea (SWYS) during April–September 2017, the spatiotemporal variations in the hydrological characteristics and nutrient conditions were coupled and analyzed; the intra-seasonal variations in the upwelling in the front of the Yellow Sea Cold Water Mass (YSCWM) and impacts on nutrient transport were explored. The coastal area was controlled by the low-salinity high-nutrient Lubei Coastal Current, Subei Coastal Current, and Yangtze River Diluted Water from north to south; at bottom, the northeastern SWYS was controlled by the low-temperature high-salinity high-nutrient YSCWM. Temperature, salinity and nutrient fronts formed around YSCWM. The upwelling velocity in the front increased during April to late June and decreased in early September; the upwelled fluxes of dissolved inorganic nitrogen (0.29×103-7.77×103 μmol·m-2d-1), phosphate (0.02×103-0.27×103 μmol·m-2d-1) and silicate (0.98×103-8.75×103 μmol·m-2d-1) showed similar variations during April–September. The upwelled nutrients could potentially contribute to local green tide development and phytoplankton growth during spring–summer.