Dissolved Silica and Its Relation to Deep-Sea Sediments: ABSTRACT

Abstract

Neither the concentration nor distribution of dissolved silica in the ocean is controlled by equilibria with solid silica or silicates. Rather, the observed pattern results from horizontal and vertical movements of oceanic water masses interacting with the formation, sedimentation, and dissolution of opaline tests of diatoms and radiolarians. Because the forces controlling this dynamic system are complex and in many cases poorly understood, it is difficult to construct a quantitative model of the present distribution pattern, or to deduce the distribution of silica in ancient oceans. The residence time of silica in seawater, a few thousand years, is short from a geologic point of view. Consequently, the ocean can have little buffering effect on the dissolved-silica cycle. The rate of supply from continental weathering, submarine weathering, or volcanism, and upward diffusion of interstitial waters must therefore be balanced by the depositional removal of opal. Because there is little evidence for dramatic changes in the rate of supply of dissolved silica to the oceans during the Cenozoic, changes in the locus of sedimentation, rather than variations in the global budget of dissolved silica, probably were responsible for variations in the nondetrital silica content of Tertiary deep-sea sediments. End_of_Article - Last_Page 342------------