Periodic Resuspension in Baltimore Canyon by Focusing of Internal Waves

High concentrations ofparticulate matter are frequently reported in submarine canyons. This study demonstrates that in Baltimore submarine canyon, elevated concentrations result from periodic resuspension events. The sloping bottom and V-shaped topography of submarine canyons could accelerate tidal flows in the canyon axis sufficiently to cause resuspension, which occurs predominantly at tidal frequencies. However, current meter and transmissometer data show that resuspension events are often associated with a borelike intrusion of cold water moving upslope near the canyon head; an event that is consistent with the focusing of internal wave energy toward the canyon head at tidal frequencies. Hydrographic onditions for the focusing of energy are most favorable in late winter and early spring when stratification in the canyon is diminished; direct observations reveal that the most pronounced resuspension events occur during those seasons. Bottom stresses generated in the canyon are sufficient to resuspend sediment along the axis at least between 200 and 800 m, with little resuspension ccurring deeper along the axis, on the canyon walls, adjacent slope, or shelf. During a resuspension event, the sediment-laden water is forced upcanyon, then sloshes back down the canyon until it reaches a layer of higher-density water, detaches from the canyon floor, and moves seaward along a density surface. This is a means of transferring sediment and associated pollutants intercepted at the canyon head to deeper water, across the shelf-slope front. Over geologic time, frequent resuspension a d seaward transport may aid in the headward erosion of submarine canyons, or at least inhibit their infilling during interglacial times.