Wind-driven motions at the mouth of the lower St Lawrence Estuary

The outflow from the lower St Lawrence Estuary (LSLE) is a major input to the Gulf of St Lawrence. The discharge of the St Lawrence River drives a pair of buoyant coastal jets in the estuary that combine to form the major part of the Gaspé Current, perhaps the dominant feature of the circulation in the Gulf. The dominant forcing agencies of the low-frequency variability (aside from the seasonal freshwater discharge cycle) of motions in the LSLE and the Gaspé Current have not been definitively identified. Here we examine current data from the mouth of the estuary from two field programs (undertaken in 1962 and 1979) and use spectral and bulk correlation analyses to show that wind-driven motions apparently exert a strong influence on the variability of the exchange between Gulf and estuarine waters. Meteorologically forced motions are shown to be most prominent in the 10- to 15-d period range (corresponding to the typical interval between the passages of weather systems). The wind-induced current field is shown to produce a counterflow at depth in the LSLE.