ACROSS-SHELF BENTHIC TRANSPORTS ON THE INNER SHELF OF THE MIDDLE ATLANTIC BIGHT DURING THE HALLOWEEN STORM OF 1991

Instrumented bottom boundary layer tripods were deployed on the inner shelf at depths of 13 m and 8 m off the U.S. Army Corps of Engineers F ield Research Facility at Duck, North Carolina, USA over a two week pe riod that included the severe and prolonged ''Halloween storm'' of lat e October 1991. The storm persisted for five days and generated waves with heights and periods of up to 6 m and 22 s. Although the instrumen tation was destroyed, current profile and suspended sediment concentra tion profile data were recovered from the 13 m site. Wind-driven mean along-shelf currents at 1.24 m above the bed attained speeds of nearly 0.5 m s-1; across-shelf flows, primarily seaward-directed, had speeds varying from 0.05 to 0.15 m s-1. These seaward flows intensified in a ssociation with groups of high waves. Total, mean current, and skin-fr iction bed shear stresses were increased, relative to moderate energy values, by more than an order of magnitude. Notably, the highest shear stresses occurred in association with high, long period swell during the late phase of the storm after winds had turned offshore creating s horeward mean flows near the bed. Suspended sediment concentrations ex ceeded 1 g l-1 throughout the lower meter of the water column and at e levations well above the top of the wave boundary layer. Net across-sh elf suspended sediment fluxes were strongly dominated by mean flows. C ospectral analyses show that important, but secondary, roles were also played by infragravity oscillations and by wave orbital velocities.