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Special Session 3: Size matters or not, particles export in marine environments |
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Abundance and sinking of biogenic silica in Daya Bay, Northern South China Sea
SS3-06-S
Xiufeng Zhao* , College of Ocean and Earth Sciences, Xiamen University
Weifeng Yang, College of Ocean and Earth Sciences, Xiamen University
Haoyang Ma, College of Ocean and Earth Sciences, Xiamen University
Min Chen, College of Ocean and Earth Sciences, Xiamen University
Presenter Email: zhaoxf@stu.xmu.edu.cn
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| Biogenic silica (bSi) is of great importance for the removal of silicon out of seawater. However, its sinking has been little investigated especially in coastal seas. Here, bSi in suspended particulate matter were examined in summer and winter in Daya Bay, northern South China Sea. The concentrations of bSi varied from 1.5 to 23.9 μmol L-1 (avg.: 8.04±5.59 μmol L-1, mean±sd, n=26) and from 0.98 to 8.69 μmol L-1 (avg.: 2.93±1.36 μmol L-1, n=35) in summer and winter respectively. Summer showed much higher bSi concentrations than winter, corresponding to the higher primary productivity in summer. These results were an order of magnitude higher than the values observed in the South China Sea. In order to evaluate the sinking or resuspension of bSi, some terms constraining advection and vertical mixing processes were included into the traditional 234Th-238U radionuclide model. For most stations, bSi showed an overall net-sinking from the water column to sediment. The sinking fluxes ranged from 0.8 to 17.1 mmol m-2 d-1 in summer with an average of 8.0 mmol m-2 d-1. In contrast, they were in the range of 0.1 to10.4 mmol m-2 d-1 with an average of 4.0 mmol m-2 d-1 in winter. At a few shallow stations, bSi showed a net-resuspension from sediment to the water column with the fluxes of 6.0-11.9 mmol m-2 d-1 (avg.: 9.8 mmol m-2 d-1) and 0.2-3.3 mmol m-2 d-1 (avg.: 1.9 mmol m-2 d-1) in summer and winter. Together with the sinking of particulate nitrogen (N) and phosphorus (P), the sinking flux ratios of N:bSi:P, on average, was 10:14:1 and 10:13:1 in summer and winter. These results indicated that particulate sinking is important to regulate the nutrient contracture in Daya Bay. This work was supported by the National Key Basic Research Special Foundation Program of China (2015CB452902 & 2015CB452903). |
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