THE SILICA BALANCE IN THE WORLD OCEAN - A REESTIMATE

The net inputs of silicic acid (dissolved silica) to the world ocean h ave been revised to 6.1 +/- 2.0 teramoles of silicon per year (1 teram ole = 10(12) moles). The major contibution (about 80 percent) comes fr om rivers, whose world average silicic acid concentration is 150 micro molar, These inputs are reasonably balanced by the net ouputs of bioge nic silica of 7.1 +/- 1.8 teramoles of silicon per year in modern mari ne sediments, The gross production of biogenic silica (the transformat ion of dissolved silicate to particulate skeletal material) in surface waters was estimated to be 240 +/- 40 teramoles of silicon per year, and the preservation ratio (opal accumulation in sediment/gross produc tion in surface waters) averages 3 percent. In the world ocean the res idence time of silicon, relative to total biological uptake in surface waters, is about 400 years.