BIOGENIC SILICA DISSOLUTION IN SEDIMENTS OF THE SOUTHERN-OCEAN .1. SOLUBILITY

A stirred how-through reactor technique was used to determine silica s olubilities in sediments collected with a multicorer in the Indian sec tor of the Southern Ocean (ANTARES I cruise). The results show that th e apparent silica solubility in the cores may decrease, increase or re main constant with depth. The silica solubility profiles are best expl ained by the early diagenetic interactions between biogenic silica and soluble aluminum derived from detrital material. By combining the sol ubility data with measured dissolved silica profiles, it is shown that the variable asymptotic pore water silica levels in the cores cannot be explained solely by differences in silica solubility. In sediments that experience a significant detrital input, the simultaneous repreci pitation of dissolved aluminum and dissolved silica prevents pore wate r silicic acid from reaching saturation with the dissolving biogenic s ilica. The principal oceanographic control on pore water silica build- up in the cores studied is the ratio of the deposition fluxes of bioge nic silica and detrital material. Solubility differences inherited fro m the biomineralization process in the surface waters do not appear to have a significant effect on the observed pore water silica levels. ( C) 1997 Elsevier Science Ltd.