Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Christopher S. Welch

Committee Member

William J. Hargis

Committee Member

John M. Zeigler

Committee Member

John A. Musick

Committee Member

Albert Y. Kuo


Results from four cruises in the outer continental shelf/slope region of the Middle Atlantic Bight demonstrate the effect of Norfolk Canyon, an east coast submarine canyon, on the exchange of local water masses. Seasonal distributions of water masses and water types around the canyon were determined from closely spaced (2-5 km) hydrographic and XBT stations. Five component water types representing shelf, winter (or cold pool), slope, warm Western North Atlantic and cool Western North Atlantic waters are defined by specific T/S signatures. The percent of each water type necessary to achieve measured T/S values along sections to the north and south of the canyon and along the canyon axis are displayed as three dimensional diagrams depicting summer, autumn and winter distributions. Results of a spring XBT survey are coupled with selected CTD cast data to determine a possible water mass distribution. The exchange of shelf and more seaward waters occurring along the canyon axis during all seasons is evident. Upwelling of Warm Western North Atlantic water occurred along the canyon axis during winter and spring while downwelling was evident under more stratified conditions encountered in summer and autumn. Winter upwelling progressed shoreward and upward at 2.5 and 1.06 x 10- 2 cm/sec. It was responsible for a short term flux of heat and salt onto the shelf which was an order of magnitude greater than estimates of the annual per kilometer rates for the entire bight attributable to cross-frontal diffusion. Summer downwelling was accompanied by a multilayered onshore-offshore exchanges of water in the upper 150 m over the canyon. Results are substantiated by volumetric T/S censuses which indicate the canyon serves as a preferential region of mixing and exchange of shelf and non-shelf waters during all seasons. An association between these exchanges and anticyclonic Gulf Stream rings is indicated.

This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.



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