Silica

Silicon is the seventh most abundant element in the universe and the second most abundant element in the Earth’s crust. It is a key nutrient element in the ocean, required for the growth of diatoms and some sponges and utilized by radiolarians, silicoflagellates, several species of choanoflagellates, and potentially picocyanobacteria. The world ocean silica cycle has been recently updated by Tréguer and De La Rocha (2013) who described and quantified source and sink fluxes.

Four pathways serve as external sources of silicic acid (also called dissolved silica, DSi) to the ocean, all of which ultimately derive from the weathering of Earth’s crust. DSi from the chemical weathering of continental rocks is discharged into the coastal zone by rivers and groundwater. Rivers also transport significant quantities of particulate amorphous silica that may dissolve, as may dust deposited on the ocean’s surface. Lastly, terrigenous silicates in sediments of continental margins may dissolve, and...