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Dissolved silica
From Wikipedia, the free encyclopedia
Dissolved silica (DSi) is the form of water soluble silica as silicon hydroxide (equivalent to the old term silicic acid), which can be measured by standard analyses (e.g. Strickland and Parsons, 1972). However, The term dissolved silica is different from the silicate occurring as silicate minerals, which is a class of minerals forming rings, sheets, chains, and tetrahedrons. Likewise, the term dissolved silica is different from the term silicone, which is organic polymers of silicon.
There exist three different species of DSi in natural waters:
- SiO2(OH)22-
- SiO(OH)3-
- Si(OH)4
Marine diatoms transport Si(OH)4 (DelAmo and Brzezinski, 2000).
In the uppermost water column the surface ocean is undersaturated with respect to DSi, except for the Antarctic Circumpolar Current south of 55°S. 
DSi is regenerated with increasing water depth, and DSi values increase along the conveyor belt from the Atlantic over the Indian into the Pacific Ocean. 
Those figures have been drawn using the interactive web site[1] which feeds on annual DSi values from LEVITUS94: World Ocean Atlas 1994, an atlas of objectively analyzed fields of major ocean parameters at the annual, seasonal, and monthly time scales. Superseded by WOA98. Edited by Syd Levitus.