SCAVENGING OF SMALL PARTICLES BY FAST-SINKING POROUS AGGREGATES

Flow through a sinking porous aggregate theoretically can increase the rate at which it collides with and sticks to smaller suspended particles. Small particles follow the flow into the aggregate and stick efficiently to aggregated material of comparable size. The scavenging efficiency, including the probability of collision and sticking, is theoretically a function of the solid fraction of the porous aggregate and the particle-aggregate size ratio. Estimates of maximum scavenging efficiencies. based on the theory of flow through a porous sphere and assumed relationships for aggregate permeability and filtration rate, are between 10(-2) and 10(-1), and thus greatly exceed theoretical collision efficiencies for impermeable spheres under similar conditions. Calculated scavenging efficiencies for diatom flocs and marine snow range from 1.8 x 10(-4) to 2.3 x 10(-2). These values are sufficiently large to make scavenging of small particles by these aggregates an important component of particle transport throughout the oceanic water column.