Volcanogenic sediment-seawater interactions and the geochemistry of pore waters

Dissolved silica concentrations were, however, significantly enriched in ash-bearing cores and showed no relation to the low but variable contents of biogenic opal. Hence, the data suggest that silica concentrations were enhanced by ash dissolution. Thus, the dissolved silica profile measured in one of the sediment cores was used to derive the in-situ dissolution rate of volcanic glass particles in marine sediments. A non-steady state model was run over a period of 43 kyr applying a constant pH of 7.30 and a dissolved Al concentration of 0.05 μM. The kinetic constant (AA) was varied systematically to fit the model to the measured dissolved silica-depth profile. The best fit to the data was obtained applying AA = 1.3 × 10−U9 mol of Si cm− 2 s− 1. This in-situ rate of ash dissolution at the seafloor is three orders of magnitude smaller than the rate of ash dissolution determined in previous laboratory experiments. Our results therefore imply that field investigations are necessary to accurately predict natural dissolution rates of volcanic glasses in marine sediments.