FY 1981

Dispersion of deep-sea mining particulates and their effect on light in ocean surface layers

Lavelle, J.W., and E. Ozturgut

Mar. Mining, 3(1/2), 185–212 (1981)

Theoretical models suited to the description of the passive dispersion of particulates are used to study vertical processes and infer horizontal length scales of deep ocean mining plumes. An analytic model of particulate dispersion in a homogeneous, advecting ocean surface layer is compared to one which incorporates a discontinuity of vertical diffusivity at the base of the mixed layer (a diffusion floor). For settling velocity magnitudes inferred from earlier test mining results and for mixed layer eddy diffusivity values typical of ocean mining areas, differences in model results are minor, suggesting the ineffectiveness of reduced vertical diffusivity in the pycnocline in retarding the vertical migration of mining effluent. For particles with smaller settling velocities, the diffusion floor can slow the clearing of the mixed layer. A horizontal length scale on the order of 100 km for a commercial mining plume is also estimated via the models. The predicted plume concentrations and a blue-light attenuation coefficient measured during test mining are used to estimate the reduction of solar radiation in the plume. Results suggest that plankton exposed to the plume might be expected to receive diminished light over an 80 to 100-h period.