Summer nitrogenous nutrient transport and its fate in the Taiwan Strait: A coupled physical‐biological modeling approach

In order to understand the fate of nutrients in the Taiwan Strait during summer, we built a coupled physical‐biological numerical ocean model, which can capture the basic hydrographic and biological features within the strait. The nutrient that we chose to model is dissolved inorganic nitrogen (DIN). The model includes individual reservoirs for nitrate (NO 3 ) and ammonium (NH 4 ). Both the observational evidence and model results show that NO 3 in the strait originates primarily from the upwelling subsurface water in the northern South China Sea (SCS) that enters the strait via the eastern and western routes separated by the Taiwan Bank. The coupled physical and biological effects on the NO 3 transport at these two routes are highlighted in the study. For the western route, the shallow topography and the coastal upwelling intensify the biological uptake of NO 3 in the whole water column. Consequently, the nitrogenous contribution by this route is mainly in form of the particulate organic nitrogen (PON). In contrast, NO 3 is transported conservatively below the nitricline at the deep eastern route, contributing the whole NO 3 supply in the TWS. The model estimates the fluxes of DIN and PON into the TWS, from the northern SCS, are 1.8 and 4 kmol s −1 , respectively. Over half (∼1 kmol s −1 ) of the DIN is synthesized into PON by the phytoplankton in the strait. Overall, this study estimates the physical and biological effects on the nutrient transport in the TWS during summer.