Subtidal acrossshelf velocity structure and surface transport effectiveness on the Alabama shelf of the northeastern Gulf of Mexico
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abstract
A 3.33 year time series of velocity and hydrographic data from a mooring site on the 20 m isobath of the Alabama shelf in the northeastern Gulf of Mexico are used to examine across-shelf circulation. The flow structure and surface transport are determined on this wide shallow shelf system, in which wind stress is a primary forcing mechanism, over a wide range of environmental conditions. The relatively long data set allows the along-and across-shelf wind stress responses to be separated so that their individual contributions to the flow structure can be analyzed. This study finds that both along-and across-shelf wind stress play a role in the across-shelf circulation. While the along-shelf wind is correlated with the currents during all seasons, the across-shelf shelf wind is most clearly correlated with the currents during fall and winter when the water column is least stratified and the across-shelf wind stress is strongest. In addition, wind stress magnitude, mid-depth vertical shear of the horizontal velocity, and stratification all show significant relationships with across-shelf transport effectiveness to varying degrees. The wide range of stratification conditions provides new insight on the influence of stratification on transport effectiveness and across-shelf wind stress forcing. Under very low stratification conditions, there is no apparent relationship between stratification and transport effectiveness, and across-shelf wind stress can generate a significant forcing contribution. As stratification increases, across-shelf wind stress becomes less important and the transport effectiveness increases to a point, above which, there is again no clear relationship with stratification. Copyright 2011 by the American Geophysical Union.
