Distribution of Biogenic Silica in Sediments

BSi concentrations in 2002 surface waters varied between 0.21 and 2.76 (tmol/L, with an averageiSD of (1.3 0.98) pmol/L. The highest concentrations of BSi were observed in coastal areas (Fig. 4.51), which were affected by 

BSi increased with depth, varying from 0.26 to 5.10 pmol/L, with an average of (1.9 1.63) imol/L, in the intermediate layer, and 1.47 to 9.19 pmol/L, with an average of (3.2 2.08) pmol/L, in the bottom waters (Fig. 4.51) (Liu et al., 2005). High concentrations of BSi in near-bottom waters are presumably due to high sedimentation rates and resuspension of bottom sediments. 

Planktonic diatoms are abundant in ECS, with Pseudo-nitzschia deli-catissma, P. pungens, and Melosira sulcata being the dominant species (Gao et al., 2003). Phytoplankton abundance was low ( 5x10 cells/L) in the coastal areas, where the SPM was high ( 100 mg/L), and the dominant species are 

Paralia sulcata and Coscinodiscus jonesianus. The distribution of chlorophyll (Chi) a during the 2002 cruise was different from that of BSi, in that the content of Chi a was high near 123° E, but low in the surface layer of the coastal areas. This is probably caused by the fact that only a small amount of BSi was bound to identifiable diatom cells in the river plume, while a large fraction of the remaining BSi consisted of disintegrated diatom cells. 

The BSi content in ECS sediments was less than 1%, which is similar to those from the Bohai and Yellow Seas, but lower than that in Jiaozhou Bay sediment (Li et al., 2006a). The low concentrations of BSi can be attributed to the high content of SPM and the shallow euphotic zone. It has been reported that iron may stimulate diatom growth and enhance nitrate uptake in coastal areas, but limited increase in silica uptake leads to rapid dissolution of BSi. 

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