Abstract: Internal Waves--Implications for Dispersal of Suspended Particulates Across Continental Shelf, with Example from Southern California
Herman A. Karl
Rapidly accelerating use of continental shelves for petroleum production and waste disposal has prompted various government studies assessing possible affects of these activities on the environment. Because solid pollutants act as suspended particulate matter, an understanding of processes influencing dispersal of suspended sediment contributes to efficient management of shelf resources. Recent field observations on San Pedro Shelf, southern California, suggest that internal waves play a prominent role in transportation of fine-grained sediment.
High-frequency internal waves propagating landward coverage on the shelf, steepen, and break where the seasonal thermocline intersects the sea bed. Data from January, August, December, and November 1974 indicate that the depth of this zone fluctuates seasonally as the thermocline migrates vertically in the water column. As internal waves shoal and break, they resuspend fines from the bottom. These particles disperse horizontally in the water column and move offshore as a turbid plume roughly coincident with the seasonal thermocline.
Effects of internal waves are not equal everywhere on the shelf. Several lines of evidence suggest that San Gabriel Submarine Canyon enhances or "focuses" energy of internal waves, thereby increasing resuspension of fines on the adjacent shelf, and acts as a sink for material "draining" to deep basins. This evidence includes tongues of turbid water 1 m above the bottom extending toward the canyon, and subtle anomalies in distribution of sediment on the shelf in the vicinity of the canyon head.
Much work needs to be done to isolate specific processes of sediment dispersal from the complex shelf system, and these investigations should receive high priority as environmental pressures mount.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC