Cross-Shelf Circulation and Momentum and Heat Balances over the Inner Continental Shelf Near Martha's Vineyard, Massachusetts

Melanie Fewings, Ph.D., 2007
Steve Lentz, Advisor

The water circulation and temperature over the inner continental shelf are investigated using six years of observations. During small waves, cross-shelf rather than along-shelf wind stress is the dominant mechanism driving cross-shelf circulation. During large waves and onshore winds the wind- and wave-driven shears cancel. During large waves and offshore winds the velocity is strongly vertically sheared because the wind- and wave-driven shears have the same sign. The subtidal cross-shelf momentum balance is a combination of geostrophy and coastal set-up by the cross-shelf wind. The estimated wave radiation stress gradient is also large. The dominant along-shelf momentum balance is between the wind stress and pressure gradient. The fluctuating along-shelf pressure gradient is a local sea level response to wind forcing, not a remotely generated pressure gradient. In summer, the water is cooled by an upwelling circulation. The cross-shelf heat flux nearly balances the surface heating in summer, so the water temperature is almost constant. The along-shelf heat flux divergence is apparently small. In winter, the change in water temperature is closer to that expected due to the surface cooling. Heat transport due to surface gravity waves is substantial.