Analysis of Suspended-particle-size Distributions over the Nova Scotian Continental Rise

Richardson, M.J. and Gardner, W.D., 1985. Analysis of suspended-particle-size distributions over the Nova Scotian Continental Rise. In: A.R.M. Nowell and C.D. Hollister (Editors), Deep Ocean Sediment Transport Preliminary Results of the High Energy Benthic Boundary Layer Experiment. Mar. Geol., 66: 189--203. The relationships of particle-size distributions to particle concentrations, silicate content and process of bo t tom boundary layer formation on the Nova Scotian Continental Rise were examined to analyze the dynamics of the benthic nepheloid layer. High particle concentrations (>400 ~g 1-') in the intense benthic nepheloid layers are nearly always associated with a coarse (-~ 8 urn) particle mode. These coarse particles must be renewed on a time scale of weeks in order to be maintained in suspension. No unique type of particle-size distribution in the benthic nepheloid layer is associated with water masses distinguished on the basis of silicate content. However, the method of formation of the bot tom boundary layer does influence the particle-size distributions. Locally mixed bot tom boundary layers are dominated by a coarse particle mode (-~8 urn). Bot tom boundary layers composed of hydrographically distinct filaments of bo t tom water mainly contain fine particles (-~ 2--3 ~m) obtained upstream. Where the filament has extremely high particle concentrations (>1 mg 1-'), the fine particle mode is masked by a locally resuspended coarse mode indicating that the filament must occasionally (within 200-300 kin) be accelerated by some external energy to the point that the critical shear stress for erosion is exceeded.