William J. Merrell

Circulation patterns inferred from the movement of detached buoys in the eastern Gulf of Mexico

Abstract The release times of five buoys, which broke free of moorings on the Alabama inner shelf, are known. The locations of subsequent sightings or recoveries of the buoys gave estimated trajectories of the buoys. These results show that the inner-shelf circulation is strongly wind-driven. When the Loop Current penetrates deeply into the northeastern Gulf of Mexico, outer shelf waters are often entrained by the Loop Current.

Transport of mud on continental shelves: Evidence from the Texas Shelf

Abstract Transmissivity and suspended-sediment data from three cruises on the East Texas continental shelf confirm that a bottom nepheloid layer (BNL) exists across the shelf; this layer is most turbid in the nearshore and outer shelf regions. In addition, surface nepheloid layers exist close to shore due to river and bay outflows, and on the outer shelf intermediate nepheloid layers are present as a result of quasi-horizontal advection from the BNL. The character of the BNL is not directly linked to local hydrography or substrate, being instead a function of the shelf dynamics. In the nearshore regime high-energy coastal processes and high sediment input from bays and rivers maintain the BNL. At the shelf edge, the BNL is formed by near-inertial internal waves and shelf waves which resuspend and transport fine sediment. Present-day sediment deposition on the East Texas Shelf can be directly related to the above processes. Mud is accumulating in the nearshore environment, due to river input, and on the inner and midshelf regions as a result of deposition from BNLs and SNLs. On the outer shelf, BNLs and INLs transport fine sediment further offshore, so that in effect suspended sediment bypasses the outer shelf.

Seasonal variability in the currents on the outer Texas-Louisiana shelf

Abstract Time series measurements of current velocity obtained at mid-depth and near the bottom (100 m) on the outer continental shelf during the spring/summer of 1980 and the winter of 1980–1981 illustrate seasonal differences in the flow regime. During the spring/summer, when the winds are from the south-east, the flow was to the east at mid-depth. During the winter, the eastward flow diminished and the water began to ‘slosh’ north/south near the shelf-edge. The beginning of the sloshing corresponded to the onset of northers but the main features of the flow do not appear to be directly forced by the local wind field. Moreover, the current meter data indicate that, at mid-depth and near the bottom, the presence of northers do not cause an increase in current speed. Superimposed on the mean flow during both deployments were oscillations with periods of a few days.