text: Five major sources of dissolved silica to the marine environment can be distinguished: 
  * Riverine influx of dissolved silica to the oceans: 4.2 ± 0.8 × 10 g SiO yr
  * Submarine volcanism and associated hydrothermal emanations: 1.9 ± 1.0 × 10 g SiO yr
  * Glacial weathering: 2 × 10 g SiO yr
  * Low temperature submarine weathering of oceanic basalts
  * Some silica may also escape from silica-enriched pore waters of pelagic sediments on the seafloor
  Once the organism has perished, part of the siliceous skeletal material dissolves, as it settles through the water column, enriching the deep waters with dissolved silica. Some of the siliceous scales can also be preserved over time as microfossils in deep-sea sediments, providing a window into modern and ancient plankton/protists communities. This biologic process has operated, since at least early Paleozoic time, to regulate the balance of silica in the ocean.
  Radiolarians (Cambrian/Ordovician-Holocene), diatoms (Cretaceous-Holocene), and silicoflagellates (Cretaceous-Holocene) form the ocean's main contributors to the global silica biogenic cycle throughout geologic time. Diatoms account for 43% of the ocean primary production, and are responsible for the bulk of silica extraction from ocean waters in the modern ocean, and during much of the past fifty million years. In contrast, oceans of Jurassic and older ages, were characterized by radiolarians as major silica-utilizing phyla. Nowadays, radiolarians are the second (after diatoms) major producers of suspended amorphous silica in ocean waters. Their distribution ranges from the Arctic to the Antarctic, being most abundant in the equatorial zone. In equatorial Pacific waters, for example, about 16,000 specimens per cubic meter can be observed.