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

Abstract

[1] 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 À1, respectively. Over half ($1 kmol s À1) 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.

Progress on upwelling studies in the China seas

“…Coupled physical and biological models have been applied to study upwelling and its associated biogeochemical responses in the Bohai Sea [ Zhang et al ., ; Wang et al ., ]. Another coupled physical‐biological numerical ocean model estimated the physical (i.e., coastal upwelling) and biological effects on nutrient transport in the TWS during summer [ J. Wang et al ., ]. These results indicated that high phytoplankton biomass appears in the upwelling region.…”

Winter bloom and associated upwelling northwest of the Luzon Island: A coupled physical‐biological modeling approach

“…To achieve a better understanding of the nutrient sources sustaining the bloom patch, we diagnosed the nutrient balance in the tracer equation from model outputs. Diagnostically, the temporal variation of nutrient concentration was decomposed into the terms presented in equation (1) [ Shchepetkin and McWilliams , ; Wang et al ., ]:…”

“…ROMS is a free‐surface, hydrostatic ocean model solving the primitive equations on topography‐following coordinates [ Shchepetkin and McWilliams , ]. The physical model was from the operational Taiwan Strait Nowcast\Forecast system (TFOR), which provides multipurpose oceanic simulations [ Jiang et al ., ; Liao et al ., ; Wang et al ., ]. Although the orthogonal curvilinear grid of TFOR (Figure a) was centered in the Taiwan Strait, the spatial resolution in the vicinity of LS was finer than 10 km and was adequate for the scope of this study.…”

“…The biological model, on the other hand, was described in Wang et al . [], which was based on the nitrogen‐based, nutrient‐phytoplankton‐zooplankton‐detritus (NPZD) model by Fennel et al . [].…”

Coastal Upwelling Off the China Coasts

“…Hydrographic and satellite data revealed evident teleconnections between the TWS upwelling and the ENSO variability. Besides, Wang et al [59] estimated the physical (i.e., coastal upwelling) and biological effects on the nutrient transport in the TWS during summer through a coupled physical-biological numerical ocean model. These studies concluded that the TWS upwelling has a profound impact on biogeochemical processes, biological productivity, and ecosystem structure.…”