Dissolved silica concentrations in pore waters from North Pacific deep-sea sediments fall into two groups. Oxidized deposits contain 22 to 35 ppm, whereas reduced sediments contain 10 to 19 ppm. All pore waters were extracted at in situ temperatures, and all sediments contain opaline silica in the form of diatom frustules and radiolarian tests. At 2°C, it appears that the pore waters are grossly undersaturated with respect to sepiolite and undersaturated relative to amorphous silica, but are slightly supersaturated relative to talc. The reduced deposits appear nearest to equilibrium with talc, suggesting that reactions in the oxidized sediments may be inhibited by “armoring” of particles by ferric hydroxide coatings.

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