SEDIMENT RESUSPENSION OVER THE CONTINENTAL-SHELF EAST OF THE DELMARVAPENINSULA

Resuspension of sediment over the continental shelf east of the Delmar va 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 va riation in the bottom stress threshold required for sediment resuspens ion at the outer shelf. This appears to be related to resuspension his tory as the largest thresholds are observed after lengthy periods with out resuspension. Episodes of shelf-wide sediment resuspension are evi denced only during very intense atmospheric storms. A 7-month-long set of records from the 90 m isobath show storm-induced sediment resuspen sion on only three occasions. The failure of storms of modest intensit y to effect resuspension al the outer shelf is largely due the decline of surface-wave currents with depth. High-frequency currents, presuma bly due to internal waves, are shown to be an important agent in initi ating sediment motion al the shelf edge. On a number of occasions, sup ertidal currents pushed the near-bottom current speed measured near th e seafloor at the 131 m isobath above the estimated level required for sediment resuspension. Numerous clouds of turbid water detected by th e light-beam attenuation records could not be attributed to local sedi ment resuspension. A probability analysis indicates that some, but not all, of these could have resulted from sediment resuspension by botto m fishing.