The supply and accumulation of silica in the marine environment

Abstract

Rivers and submarine hydrothermal emanations supply 6.1 × 10 14 g SiO 2/yr to the marine environment. Approximately two-thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep-sea deposits. Siliceous deep-sea sediments located beneath the Antarctic Polar Front (Convergence) account for over a fourth (1.6 × 10 14 g SiO 2/yr) of the silica supplied to the oceans. Deep-sea sediment accumulation rates beneath the Polar Front are highest in the South Atlantic with values as large as 53cm/kyr during the last 18.000 yr. Siliceous sediments in the Bering Sea, Sea of Okhotsk, and Subarctic North Pacific accumulate 0.6 × 10 14 g SiO 2/yr or 10% of the dissolved silica input to the oceans. The accumulation of biogenic silica in estuarine deposits removes a maximum of 0.8 × 10 14 g SiO 2/yr. Although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters, the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters. Siliceous sediments from continental margin upwelling areas (e.g. Gulf of California, Walvis Bay, or Peru-Chile coast) have the highest biogenic silica accumulation rates in the marine environment (69 g SiO 2 cm 2/kyr). Despite the rapid accumulation of biogenic silica, upwelling areas account for less than 5% of the silica supplied to the marine environment because they are confined laterally to such small areas.