INTERACTION OF MARINE SEDIMENTS WITH DISSOLVED SILICA1

A sample of Atlantic sea floor sediment released SiO2 in amounts greater than expected when placed in contact with silica‐poor seawater but failed to reduce the concentration of enriched (211 μm) seawater. In situ, these sediments had been in contact with seawater containing 30‐µm silica. The interstitial water from the core held 210‐µm silica, suggesting that clay‐silica equilibria control this concentration. If this interstitial silica were derived from resolution of clay minerals, then clay‐silica equilibria would be a major source of dissolved silica in the Atlantic Ocean. It is far more likely that the resolution of biological silica accounts for the bulk of the interstitial content and this mechanism might explain the high silica concentrations found in cores from productive regions. In barren areas, the lower interstitial concentrations may be regulated by clay‐silica equilibria. The relative amounts of dissolved silica entering the oceans (~4 × 1014 g/yr) compared to the amount of pelagic clay sedimentation (~2 × 1015 g/yr) indicate that clay—if it were the major agent of removal—would have to contain 20% hydrogenous silica, whereas the maximum demonstrated adsorption is about 2%. It seems impossible that adsorption on clays is the prime agent for extraction of silica from the present oceans.