Atmosphere–Ocean Coupling in the Northern Gulf of St. Lawrence: Frequency-Dependent Wind-Forced Variations in Nearshore Sea Temperatures and Currents

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Abstract
We found nearshore sea temperatures and currents on the north shore of the Gulf of St. Lawrence to be linked to wind-forced upwellings and downwellings. Multiple coherence of alongshore and cross-shore wind stresses with sea temperature (f > 1/d removed) was significant at periods > 3 d (maximum K2 = 0.90) and at 1.8 d. Partial coherences were frequency dependent. At periods > 3 d, which contained most of the variance alongshore forces dominated. Cross-shore winds were significant only at 1.8 d. A time domain model using lagged wind stress and cumulative air temperature as predictors explained 95% of the variance in post-stratification nearshore temperature. Temperature changes were virtually synchronous along 150 km of coastline. Alongshore currents were coherent with alongshore winds at periods > 2 d. Cross-shore currents were coherent with cross-shore winds at periods of 1–2 d. These results are compared with Csanady's models of wind-forced coastal thermocline oscillation. We conclude that alongshore winds force major upwellings and downwellings in this region. Cross-shore forces are important at f > 0.5/d. These dynamics regulate local primary biological processes and the transport of energy through their influence on fish migration.