Tidally Modulated Internal Hydraulic Flow and Energetics in the Central Canadian Arctic Archipelago

The Canadian Arctic Archipelago is a key conduit for comparatively fresh Arctic waters flowing to the Atlantic. Model estimates of the freshwater outflow, which is strongly correlated with the volume flux, contain major uncertainties because most existing models exclude tides, marginally resolve the internal Rossby radius, or both. At the same time, barotropic tidal models preclude stratified flow effects. Here we assess the relative importance of barotropic and baroclinic processes to water mass transformation, friction, and energy losses motivated by processes observed in a fine-scale survey in the central Archipelago. A sharp separation of warmed Canada Basin water and locally formed water is observed over a long sill in a narrow channel and coincides with an internal hydraulic jump caused by the mean flow. Tidal currents, however, modulate the jump, as demonstrated by both scale analysis and a two-dimensional simulation. The jump, together with internal tides propagating as Kelvin waves, leads to isopycnal displacements up to 50m. The generation of these internal Kelvin waves has a leading-order role in a regional energy budget. It is small, however, relative to bottom boundary layer dissipation, which accounts for an estimated 50% of the total tidal energy losses. Consequently, adding tides needs to be a priority for regional models. Plain Language Summary Satellite and in situ observations indicate that the western Arctic Ocean is growing fresher. One of two pathways that this freshwater can take to the Atlantic Ocean is the Canadian Arctic Archipelago, which includes many constrictions that induce energetic turbulence. Predicting this outflow is a great challenge to large-scale numerical predictions due to poor parameterization of this mixing and friction, with consequences for global climate prediction. Using high-spatial-resolution observations of salinity, temperature, and velocity, we show the importance of mean flow and tidal processes in the straits in causing turbulence and dissipation. In particular, we show evidence that radiating internal waves, breaking hydraulic lee waves, and bottom friction all play leading-order roles in the energy budget and mixing of water in the region.