Coastal upwelling and eddy development off Nova Scotia

Abstract

Satellite photos during the summer of 1984 show the development of a band of cool water along the seaward coast of Nova Scotia during a month‐long period of upwelling favorable winds. The timing of the appearance of the cool water band, the rate at which it broadened, and the bottom‐temperature evolution at several representative points along the coast are shown to be in good agreement with an idealized two‐layer model of the wind‐driven shelf circulation. The presence of the cool water is clearly attributable to upwelling. After the temperature front moves offshore, wavelike features develop rapidly with alongshore wavelengths of 50–75 km and similar maximum cross‐shore displacement amplitudes. The associated alongshore propagation speed is at most 0.02 m s−1 to the northeast. The length and time scales of these features are shown to be consistent with results from simple linear instability models which allow for both potential and kinetic energy release from the mean state by perturbations. Results suggest that the wavelike features are primarily due to baroclinic instability of the upwelling‐associated base state. Rough estimates suggest that upwelling and subsequent eddy development can play an important role in the supply of nutrients to the surface waters of the shelf.