Distribution and dissolution process of biogenic silica in the Suruga Bay

Distribution and dissolution process of biogenic silica (BSi) were investigated in the Suruga Bay. BSi concentration in the upper 200 m changed seasonally and ranged from 0.06 to 0.82 μmol/l. Vertical distribution of BSi had some peaks and marked the minimum concentration at 200-300 m. BSi concentration increased with depth below 200-300 m. In the dissolution experiments of BSi using natural seawater,BSi concentration decreased more slowly than particulate organic carbon (POC). BSi dissolved most intensively in the surface water (20 m), following the seawater taken at 150 m and 800 m. Dissolution rate constant of BSi varied among the sampling periods, and the values during the first 14 days ranged from 0.026 to 0.052 day^<-1> as for the surface water. Rate constant of BSi dissolution and POC degradation had similar seasonal variations under the same temperature. This result suggests that dissolution of BSi would be regulated not only by temperature but also by degradation of POC, that is, bacterial degradation of organic matrix in diatom cells. Our estimation of dissolved BSi via biological process accounts for 46-47% of total dissolution over 70 days in the surface water. This suggests that much of the BSi dissolution would be biologically mediated in marine environment.publishe