Exchange of water between the Keweenaw Waterway and Lake Superior: Characteristics and forcing mechanisms

The Keweenaw Waterway is a navigation passage with openings to Lake Superior at either end. Analysis of wind data and moored thermistor measurements indicates that movement of water into and out of the waterway is strongly influenced by surface winds through at least two mechanisms. One is direct forcing of waterway flows by the surface wind stress. The other is flow driven by pressure gradients arising from wind-driven changes in coastal lake level. Not surprisingly, the relative importance of direct wind forcing in driving near-entry flows appears to diminish with increasing depth. Also indicated is a tendency for winds to generate counterbalancing flows at the two entries, with wind-driven inflow at one entry matched by wind-driven outflow at the other entry. On a number of occasions, temperature data indicate flow out of the waterway entering a coastal water column modified by upwelling. This is presumably because upwelling favorable winds tend to depress coastal lake level, and create a pressure gradient driving flow out of the waterway