REACTIVE SURFACE-AREA CONTROL OF THE DISSOLUTION KINETICS OF BIOGENICSILICA IN DEEP-SEA SEDIMENTS

Flow-through dissolution experiments demonstrate that the specific rea ctive surface area of biogenic silica decreases significantly with dep th in surficial sediments of the Southern Ocean. Specific surface area s obtained from nitrogen gas BET adsorption isotherms, however, do not exhibit the systematic changes of the specific reactive surface area inferred from the kinetic experiments. Furthermore, the decrease in su rface reactivity of the siliceous skeleton fragments continues at dept hs in the sediments where there is no longer a net release of silicic acid to the pore waters. Thus, the specific reactive surface changes m ost likely reflect a progressive reduction of the surface density of r eactive sites (aging) during burial, rather than the preferential diss olution of a more reactive fraction of siliceous debris deposited from the water column. The observed aging of the silica surfaces has impor tant consequences for the benthic regeneration of nutrient silicic aci d from deep-sea sediments.