| dc.description.abstract | Abstract
A coupled physical-biogeochemical model has been used to simulate the distributions of nutrient(i.e. DIN, dissolved inorganic nitrogen) and chlorophyll(Chl-a) in the East China Sea and to predict primary productivity(Liu et al.,2010). Concentrations of DIN, Chl-a and the integrated primary production(IPP) are similar to observations of Gong et al.(2003). However, the model relies on nudging towards observed climatological distribution DIN. Without nudging, the modeled DIN is much higher than observations near the Changjiang river mouth and much lower than observations in most of the far field. The mostly underestimated DIN causes underestimating Chl-a and PP. The high values in the near field result from the high DIN concentration of the ChangJiang run off prescribed for the model.
Since Changjiang estuary is an estuary of medium tidal range, its tidal action can influence the dispersal of Changjiang plume. In this study, we add the tidal action in the ECSmodel to explore how tidal action influences the biochemistry of the East China Sea and compare the output with observations. The tidal action is incorporated in the model by prescribing the sea level changes caused by tides on the open boundaries, so that the tidal actions may propogate into the model domain.
The tidal action makes the Changjiang plume more dispersive and better resembling observations. In addition, it induces stronger horizontal and vertical mixing so that the distribution of DIN concentration in the surface layer close to the observations. On the other hand, the total DIN in the upper 60m remains nearby the same, indicating the tidal action merely moves. DIN from the subsurface layer to the surface layer, which enhances photosynthesis. The additional concentration of DIN in the surface layer increases the IPP by 40% on an annual basis. The modeled annual mean IPP reaches 93% of the observated mean value.
For the water depth of 0 ~ 30m, the mean concentration of modeled DIN increases from 1 ?m to 2 ?m in the ECS shelf region by tidal action. From Michaelis-Menten kinetics, the phytoplankton growth rate can reach 91% of maximam phytoplankton growth rate, which may explain the enhanced primary productivity.
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