Global Pools and Fluxes of Silicon

The average Si content in terrestrial biomass is 0.5% (on dry mass basis) that corresponds to 12.5 X 10 tons. In marine plankton the average content is 5% and relevant pool is 0.17 x 10 tons. The annual biological Si cycle in the global terrestrial ecosystem takes about 0.9 x lO tons/yr. 

Neutral hydroxide Si(OH)4 is predominant in the natural water, the content of anion Si(0H)30 is in a lesser degree. The continental river water discharge is responsible for 0.2 x 10 tons of soluble silicon species. The mass of Si compounds in the ocean is 4, 110 x 1tons, and the residence time of Si in the marine waters is 20,550 years. The transport of silicon from terrestrial to oceanic ecosystems is not counterbalanced by the reverse transport. In addition to the soluble species, the content of silicon in river particulate matter is about 120 /rg/L. This gives the elemental transport of 4.8 x 10 tons/yr. The total estimate of river water fluxes from the global land area to the ocean is 5.0 x 10 tons/yr. Aeolian migration of silicon is responsible for 0.47 X 10 tons per year. It means the annual global land losses (river and wind fluxes) are 5.47 x 10 tons (Dobrovolsky, 1994). 

The soluble Si species in the global ocean account for less than 0.001 % of the mass of this element in sedimentary rocks. According to Ronov (1976), the mass of sedimentary rocks contains 44.03% 0fSiO2, which corresponds to 493.6 x lO - tons of silicon. The total pool of this element in the granite layer and sedimentary shell amounts to 2.918 x lO tons (Table 28). 

Modem calculations show that during the Earth s geological history about 17% of the total mass of silicon has been release via geochemical and biogeochemical cycling. 

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