Lithogenic silica

Lithogenic silica (LSi) is silica (SiO2) derived from terrigenous rock (Igneous, metamorphic, and sedimentary), lithogenic sediments composed of the detritus of pre-existing rock, volcanic ejecta, extraterrestrial material, and minerals such silicate. Silica is the most abundant compound in the Earth's crust (59%) and the main component of almost every rock (>95%). Lithogenic Silica in Marine Systems LSi can either be accumulated "directly" in marine sediments as clastic particles or be transferred into dissolved silica (DSi) in the water column. Within living marine systems, DSi is the most important form of silica Forms of DSi, such as silicic acid (Si(OH)4), are utilized by silicoflagellates and radiolarians to create their mineral skeletons, and by diatoms to develop their frustules (external shells). These structures are vitally important, as they can protect, amplify light for photosynthesis, and even help keep these organisms afloat in the water column. DSi more readily forms from biogenic silica (BSi) than from LSi, as the latter is less soluble in water. However, LSi is still an important supply to the silica cycle, due to it being a primary supplier of silica to the water column. Sources Rivers are one of the major suppliers of LSi to marine environments. As they flow, rivers pick up fine particles, such as clays, silts, and sand, through physical weathering. Lithogenic silicic acid forms through chemical weathering, as CO2-rich water comes into contact with silicate and aluminosilicate minerals from terrestrial rocks. The silicic acid is then transported to the river via runoff or groundwater flow before being transported to the ocean. Estimates of combined flux (both lithogenic and biogenic) report that about 6.2 ± 1.8 Tmol Si year−1 and 147 ¨ ± 44 Tmol Si year−1 of dissolved and particulate silica, respectively, enter estuaries. Eolian transport occurs when wind picks up weathered particles, primarily lithogenic, and transports them into the atmosphere, from which they subsequently fall into the ocean. The solubility of the silica within such sediments depends on both the origin and composition of the material. For example, studies of Saharan sediment, which is mostly made of quartz, found a solubility range of 0.02%-1.1%, while some feldspar-rich sediment was estimated to have a solubility of about 10%.