Tidally‐Modulated Turbidity and Density Fluctuations in a Rotationally‐Modified Gravity Current

Abstract

AbstractRotationally‐modified gravity currents are known to occur on the ocean bottom in many locations around the world. Although their time scales are long enough that the Coriolis force is important in their dynamics, tidal forcing may also play a role in intermediate‐term variability by periodically enhancing or diminishing the flow and bottom friction, although the importance and implications of this variability has not previously been studied. Here we investigate hourly‐to‐tidal variations in the turbidity and density of intermittent gravity currents associated with deep‐water renewal events in the Strait of Georgia, Canada. We find that features such as the height and magnitude of the gravity current's nose, as well as bottom stress, undergo tidal variations, and that sediment resuspension largely occurs at the times of greatest stress at peak flood, with highest turbidities occurring in the hours following that peak. Larger particles soon settle again, but smaller ones can remain suspended. In addition, there is a significant tidally‐driven lateral advection of the gravity current, which results in density fluctuations in observations at a fixed location.