Near-Bottom Cross-Shelf Currents in the Northwestern Gulf of Mexico: A Response to Wind Forcing

Ned P. Smith Port Aransas Marine Laboratory, The University of Texas, Port Aransas, Tex. 78373

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Abstract

Recording current meter data from two near-bottom levels on the inner shelf of the northwestern Gulf of Mexico are presented with wind data from November and December 1975. Four periods of predominantly cross-shelf motion are discussed, involving both onshore and offshore motion. Coherence spectra relating cross-shelf motion with the longshore and cross-shelf components of the computed wind stress show statistically significant values at both levels. Cross-shelf motion past the upper current meter, 3.7 m above the bottom in 13.5 m of water, is more responsive to the cross-shelf component of the wind stress and indicates that near-bottom cross-shelf motion occurs as a simple return flow. At the lower level, 0.9 m above the bottom,, cross-shelf currents are more coherent with the longshore component of the wind stress, suggesting a response to Ekman transport in the surface layer. A coherence spectrum of cross-shelf motion from these two levels indicates low values except over the very longest time scales.

Abstract

Recording current meter data from two near-bottom levels on the inner shelf of the northwestern Gulf of Mexico are presented with wind data from November and December 1975. Four periods of predominantly cross-shelf motion are discussed, involving both onshore and offshore motion. Coherence spectra relating cross-shelf motion with the longshore and cross-shelf components of the computed wind stress show statistically significant values at both levels. Cross-shelf motion past the upper current meter, 3.7 m above the bottom in 13.5 m of water, is more responsive to the cross-shelf component of the wind stress and indicates that near-bottom cross-shelf motion occurs as a simple return flow. At the lower level, 0.9 m above the bottom,, cross-shelf currents are more coherent with the longshore component of the wind stress, suggesting a response to Ekman transport in the surface layer. A coherence spectrum of cross-shelf motion from these two levels indicates low values except over the very longest time scales.

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