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Book Chapter

Shelfedge Dynamics and the Nepheloid Layer in the Northwestern Gulf of Mexico

By
David W. McGrail
David W. McGrail
Department of Oceanography, Texas A&M University
College Station, Texas 77843
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Michael Carnes
Michael Carnes
Department of Oceanography, Texas A&M University
College Station, Texas 77843
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Published:
January 01, 1983

ABSTRACT

An investigation of shelfedge sedimentary processes in the Gulf of Mexico has been underway for the past five years. It has consisted of in situ bottom boundary layer (BBL) experiments, time series observations using moored instruments, and hundreds of hydrographic stations. A ubiquitous nepheloid layer exists over the outer continental shelf in the BBL. It reaches a maximum thickness of 30 m when offshore flow near bottom stacks detached bottom boundary layers at the shelfedge. The shear stresses which maintain the sediment suspension are contributed by a superposition of many modes of motion. In the northwestern Gulf of Mexico, surface gravity waves, high frequency internal waves and tides do not appear to contribute significantly to the sedimentary processes at the shelfbreak. However, diurnal inertial oscillations do resuspend silt and clay at the shelfedge and transport that sediment to the offshore. Winter storms produce three types of phenomena that influence sediment transport: (1) direct, energetic, cross-shelf wind-driven flow; (2) production of dense, cool, saline bottom water that flows offshore under the influence of gravity; and (3) inertial oscillations which propagate to the bottom. The mean shelfedge flow was found to be west to east in the interior, with bottom waters oriented more southeasterly. The latter should contribute to a long term advection of sediment off the shelf. Flow on the bottom of the upper slope has been observed to be oriented to the northeast, suggesting a convergence in the BBL near the shelfbreak.

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SEPM Special Publication

The Shelfbreak: Critical Interface on Continental Margins

Daniel Jean Stanley
Daniel Jean Stanley
Division of Sedimentology Smithsonian Institution
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George T. Moore
George T. Moore
Chevron Oil Field Research Company La Habra California
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SEPM Society for Sedimentary Geology
Volume
33
ISBN electronic:
9781565761636
Publication date:
January 01, 1983

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