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Articles by Shiyu Li
Total Records ( 2 ) for Shiyu Li
  Bingxu Geng , Shiyu Li , Dongxiao Wang , Jiatang Hu , Lin Luo and Siying Wang
  The South China Sea is an oligotrophic marginal sea located in the tropical-subtropical Northwestern Pacific Ocean. Under the influences of monsoon winds, both the physical and biogeochemical processes exhibit distinct seasonal variability in the upper waters. In order to study the seasonal variations of surface phytoplankton, a one-dimensional coupled physical-biogeochemical model was developed and applied to the deep basins of the Northern South China Sea, away from the coastal upwelling regions. Forced under real-time surface monsoon winds and heat flux, the model reproduced the mixed layer depth, sea surface temperature and surface chlorophyll-a compared with satellite observations and previous reported values. In seasonal mean, the mixed layer depth was highest in winter (61.62 m) and lowest in spring (12.07 m). The sea surface temperature was lowest (25.05°C) in winter and highest (29.20°C) in summer. Furthermore, conspicuous phytoplankton blooms occurred in winter with the highest chlorophyll-a concentration up to 0.21 mg m-3. In other seasons, the concentration remained relatively low, especially in summer (0.05 mg m-3). The spatial distributions of phytoplankton were closely related with patterns of surface nutrient availability, as well as mixed layer depth and sea surface temperature. These relationships indicate that surface phytoplankton primary production was mainly controlled by nutrient availability, which was dominated by vertical turbulent diffusion in the deep basin of the northern Sea which is away from the coastal upwelling regions. Overall, our model results indicated that the seasonal variability of surface phytoplankton was modulated by coupled effects of physical and biogeochemical processes in the Northern South China Sea.
  Heng Zhang and Shiyu Li
  Hypoxia in the Pearl River Estuary (PRE) during summer is one of the problems caused by increasing anthropogenic pollutant inputs due to population increase and economic development in recent years. The mechanism for hypoxia in the PRE has to be understood firstly before any management policy can be established. A three-dimensional water quality model was therefore developed to study the dissolved oxygen (DO) budget of the PRE in summer and to identify the roles that various physical and biochemical processes played in DO dynamics.

Results show that above the pycnocline, horizontal transport of DO is mainly balanced by reaeration, and photosynthesis appears to play a more important role in the shelf area than inside the PRE due to reduced turbidity. Below the pycnocline, horizontal transport of DO is balanced by biochemical processes. Regarding the DO depletion processes in the PRE above the pycnocline, DOC oxidation is the largest consumer of DO, while nitrification and phytoplankton respiration rank second and third, respectively. Below the pycnocline, SOD dominates DO depletion processes, following by DOC oxidation, nitrification and phytoplankton respiration. The dominant role of SOD in DO depletion processes of the PRE is caused by the shallow topography and high deposition rate of POC. Vertical DO transport in the PRE shows remarkably spatial variability due to complicated hydrology and topography in the PRE. The vertical DO fluxes are dominated by advective fluxes as a result of intense tidal forcing and gravitational circulation in deep channels, while diffusive fluxes dominate in the vertical fluxes within the shoal area as a result of increasing DO vertical gradient due to hypoxia.

 
 
 
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