| Remotely- and locally-generated semidiurnal internal tides superpose to create a complex breaking internal wavefield on the Oregon continental slope. Presented here are observations between the 500-3000 m isobaths from a zonal line of 5 full-depth profiling moorings, an 18-hour XCP survey and five 15-25 hour LADCP/CTD stations. The 40-day moored deployment spans three spring and two neap tides, during which internal tides are predominantly locally- and remotely-generated, respectively. When local generation is strong during local spring tides, energy flux over the slope is predominantly offshore (westward) consistent with locally-generated internal tides propagating offshore. During local neap tide, when local generation is weak, energy flux is predominantly onshore (eastward), consistent with shoaling remotely-generated internal tides. Remotely-generated internal tides also propagate onshore during the first spring tide and lack a spring-neap cycle, making them likely to come from multiple sources. At the deep mooring, 100 km offshore, remotely-generated internal tides initially propagate northward and are turned onshore by reflection from large-scale bathymetry. This is verified with a simple three-dimensional model of mode-1 internal tides propagating obliquely onto a super-critical slope. Where the slope is super-critical, internal tides break forming turbulent upslope internal bores between the 1200-1800 m isobaths. A snap-shot of a single bore is captured in a 25-hour LADCP/CTD station at the 1200 m and composites are made from MMP profiles at the two deepest slope moorings. In general, bores are cold, salty, over 100 m thick, and have a turbulent head which suspends sediment. Dissipation rates and diapycnal diffusivities increase when bores are present (epsilonbores > 10-8 W kg-1 and Kboresr > 10-3 m s-1) and are sufficiently elevated to completely dissipate the northbound 0.2 kW mode-1 internal tide before the 1000-m isobath. Supercritical continental slopes may therefore be important internal tide sinks. |
