Particle-size distributions within hydrothermal plumes over the Juan de Fuca Ridge

Abstract

The particle-size distributions of suspended particles in neutrally buoyant hydrothermal plumes from two vent sites on the Juan de Fuca Ridge were measured with a Coulter counter. Hydrothermal particle populations were characterized by high volume concentrations of particles with diameters of <2 μm. Particle populations dominated by larger particles were rare and observed only very near active vent sources because of rapid settling and dilution. Particle-size distributions from particle plumes of hydrothermal origin can be readily distinguished from those of benthic nepheloid layers by the fine-particle tail, which is expressed on a cumulative number distribution by a slope much steeper than the oceanic norm of ≈3. The predominance of particles with diameters <2 μm within neutrally buoyant hydrothermal plumes demonstrates that the bulk of hydrothermal precipitates are capable of being dispersed over wide areas.