Particle settling through a diffusive-type thermohaline staircase in the ocean

Sedimentation through a “diffusive”-type thermohaline staircase in the ocean is investigated experimentally and theoretically. The experiments span a wide range in the density ratio that controls the stability of the interface between the convecting fluid layers (1.1 < Rϱ < 2.5). In each experiment, it is found that the number of particles in a convecting layer decreases exponentially with time, with a decay rate equal to the settling velocity divided by the depth of the layer. This result is identical to that seen for sedimentation onto a rigid boundary, and is due to the small magnitude of the vertical component of the rms convectine velocity in the vicinity of the interface. A theoretical analysis is also used to quantify the rate of sedimentation through a staircase with several convecting layers. As the number of layers in the staircase is increased, the rate of sedimentation is found to steadily approach the rate of sedimentation in a non-convecting fluid.