Sediment resuspension over the continental shelf east of the Delmarva Peninsula

Resuspension of sediment over the continental shelf east of the Delmarva Peninsula has been examined using records of light-beam attenuation, near-bottom current speed and surface-wave height spectra collected during 1988 and 1989. These data give evidence of a factor of three variation in the bottom stress threshold required for sediment resuspension at the outer shelf. This appears to be related to resuspension history as the largest thresholds are observed after lengthy periods without resuspension. Episodes of shelf-wide sediment resuspension are evidenced only during very intense atmospheric storms. A 7-month-long set of records from the 90 m isobath show storm-induced sediment resuspension on only three occasions. The failure of storms of modest intensity to effect resuspension at the outer shelf is largely due the decline of surface-wave currents with depth. High-frequency currents, presumably due to internal waves, are shown to be an important agent in initiating sediment motion at the shelf edge. On a number of occasions, supertidal currents pushed the near-bottom current speed measured near the seafloor at the 131 m isobath above the estimated level required for sediment resuspension. Numerous clouds of turbid water detected by the light-beam attenuation records could not be attributed to local sediment resuspension. A probability analysis indicates that some, but not all, of these could have resulted from sediment resuspension by bottom fishing.