Biogenic Silica In The Jiaozhou Bay

Biogenic silica (BSi) is produced in the euphotic zone of the ocean by siliceous plankton such as diatoms or radiolarians. Due to the major role played by diatoms in the biological pump of CO₂, biogenic silica may has a close coupling in the global carbon cycle. In addition, the accumulation of biogenic silica on the ocean floor can reflect the spatial and temporal distribution of productivity. In the past 40 years, the great change of nutrient structure has lead an obvious effects on the Jiaozhou Bay ecosystem, the silicate cycling has received significant scientific attention. An improved method is applied to the study of BSi in Jiaozhou Bay, the relationship between BSi and the phytoplankton, nutrient and organic carbon were discussed, the BSi cycle was studied simply.The comparison for the measurement of BSi demonstrated that the non-biogenic silica extracted from clay minerals had obvious effects on determinations of BSi-poor samples. No significant difference in BSi extracted has been found for solid-solution ration between 1.25 and 5g/L. The influence of adsorption loss and centrifugation can also be negligible. The technique we used has high accuracy even for the sample with very low BSi contents of3^2- and paniculate biogenic silica(PBSi) in water colum, and content of BSi in the sediment were investigated in Jiaozhou Bay in August -November 2001 and September 2002.The contents of SiO₃^2- are high near the west bank and northeast corner of the bay and much lower in the other area. The seasonal variation of phytoplankton biomass is an important reason inducing the difference in contents of SiO₃^2-between summer and autumn. The flux of silicic acid from main rivers around Jiaozhou Bay can reach 28.67 X 10⁴mol/d.The concentration of PBSi in Jiaozhou Bay seawater varies from 0.08 to 5.38μmol/L, with 1.96μmol/L as the mean value. Higher PBSi concentrations were found at north and northeast side of the bay, while lower at the central section. Verylow biogenic silica contents of less than 1 wt.% were observed in sediments. The distribution of BSi in sediments is similar with that in water. Measurements of sedimentary BSi in the Jiaozhou Bay provide that the changes in BSi accumulation can used to infer increased diatom production and sedimentation resulting from nutrient enrichment.BSi in sediment and water has close relationship with the phytoplankton, nutrient and organic carbon. For the decrease of the ratio of Si/C, C/N from water to sediment, it is suggested that organic carbon is recycled more rapidly than biogenic silica, while organic nitrogen is recycled faster than organic carbon. The incubation of biogenic silica shows the same results.With the rates of silica regeneration in the seabed, biogenic silica cycle in Jiaozhou Bay was studied. According to estimate, only 15% of the BSi produced in the surface sea accumulates in the sediment with the remainder returning to the water column as a result of dissolution. The regeneration of BSi accounts for 39% of the silica reaching the seabed.