Evidence of wind-driven upwelling in Jacques-Cartier Strait

Satellite images of the Gulf of St. Lawrence show a persistent band of cold water along the north coast of Jacques-Cartier Strait during summer. A possible explanation is that the wind is causing upwelling of deep water. The upwelling hypothesis is tested here by comparing along-shore wind stress time series tau(r)(t) with upwelling velocity w(t) inferred from moored temperature data with a regression model. The results support the upwelling hypothesis. For periods exceeding 1.5 d (e.g. wind-event periods), the average spectral coherency between along-shore wind stress and inferred upwelling velocity is 0.76, which exceeds the 5% significance level of 0.52. The cross-shore length scale of upwelling, L, inferred from combining the transfer function between w and tau(r) with the upwelling model, w = tau(r)/rho f L, was calculated as 4 to 7 km. This is comparable to the Rossby radius, further supporting the upwelling hypothesis.