Current variability and upwelling along the north shore of baie des chaleurs

Abstract

The circulation and temperature variability along the north shore of Baie des Chaleurs is investigated from the first extensive set of moored current‐meter data. Instruments were deployed from July to December of 1985, 1986 and 1987 at three locations. The moorings were placed within an internal Rossby radius of deformation of the coast and the sites had a total alongshore separation distance of 100 km. The currents were primarily directed alongshore and the variability was dominated by the tides. The tidal amplitudes were 0.05–0.25 m s‐1 in contrast to low‐frequency (periods above 1 d) speeds that were typically <0.04 m s‐1. The mean residual currents ranged from 0.01–0.1 m s‐1 and are shown to dominate the advective displacement of passive particles for periods above 5 d. The mean circulation was westward in summer but reversed in early autumn in the outer half of the bay. The westward flow is believed to be an extension of the Gaspé Current. A reduction in the strength of the Gaspé Current, coupled with an increase in the eastward wind stress, is proposed as the cause of the flow reversal in autumn. Large‐amplitude temperature fluctuations were observed at periods of 5–10 d with high coherence between sites. The temperature oscillations were generated near the mouth of the bay by alongshore winds and propagated westward along the north shore at the internal gravity wave speed. These properties are consistent with those of an internal Kelvin wave, although modification by topographic influences is likely. Wind typically accounted for 40–65% of the observed temperature variance. © 1993 Taylor & Francis Group, LLC.