Chang et al.: Sediment resuspension on the Middle Atlantic Bight continental shelf during Hurricanes Edouard and Hortense: September 1996


The present comprehensive physical and optical measurements have captured sediment resuspension events associated with two hurricanes, Edouard and Hortense, that passed over the Coastal Mixing and Optics study site in the fall of 1996. Sediment resuspension associated with Hurricane Edouard was forced by both current and wave processes. Combined current-wave bottom shear stresses exceeded 3.5 dynes cm^-2, well above the critical shear stress for resuspension, which was determined to be 0.8 dynes cm^-2. Hortense sediment resuspension, however, was caused primarily by waves with little or no interaction with mean-currents; combined current-wave bottom shear stress reached 2 dynes cm^-2. Beam attenuation data reveal that bottom sediments were resuspended from ~70 m depth to more than 30 m up into the water column during both hurricanes. The relaxation of sediments to pre-Edouard conditions occurred at about the same time at all depths, indicating advection and transport by mean-currents. The relaxation time of sediments to pre-Hortense conditions, however, was different at each depth suggesting settling throughout the water column. Analyses of optical data reveal that the resuspended sediments consisted mainly of detritus and relict pigments from the ocean bottom.