A particle sedimentation model of buoyant jets: observations of hydrothermal plumes

We extend the application of exponential settling to hydrothermal plumes to predict hydrothermal sediment patterns on the seafloor by using acoustic observations of particle velocities and concentrations instead of the predictions of dynamic models used by previous studies. We assume settling occurs only from the margins of the plume, which corresponds to the transition from a net upwards force on the particles in the plume to a net downwards force outside. In each volume element where the net force changes from downwards to upwards, the loss of sediment from the volume element is calculated. The losses for five particle sizes are summed to determine the sediment mass deposited. We applied this sedimentation model to acoustic observations of particle concentration and flow velocity in hydrothermal plumes at Grotto Vent on the Endeavour Segment of the Juan de Fuca Ridge. The overall mass flux decreases if the particle size distribution is shifted towards smaller particles or particle density is decreased (as for biological particles). While improvements in both observations and model algorithms are needed, we demonstrate that quantitative predictions of sedimentation can be made successfully from direct observations of plumes.