Stationary Internal Tides Observed in a Steep, Reflective, Coastal Submarine Canyon
Internal tide stationarity is examined by comparing isopycnal displacement (η) band-passed between 6 and 30 hours to harmonic fits computed over a range of fit windows between 3 and 90 days. At a mooring 22 km away on the open shelf, the average skill of harmonic fits to η over a 90-day fit window is 19%; within the canyon that value increases to 50%—very high when compared to most other coastal mooring records that have been similarly assessed and indicating surprisingly high internal tide stationarity in the canyon. Phase offsets between TPXO surface tides and harmonic fits at a given depth are relatively constant and consistent with arrival times expected for internal tides being generated at a steep shelf edge nearby.
Relatively stationary internal tides contribute to clear spring-neap cycles in depth-integrated energy, energy flux, stratification, and dissipation occur at times throughout the year. Depth-integrated chlorophyll fluorescence [Chl] also demonstrates spring-neap variability, and maxima in [Chl] lag behind maxima in semi-diurnal energy by 2-3 days.
Long time series within canyon systems are rare, and these results could motivate an investigation into whether the skill of internal tide predictions may be useful near canyon systems or steep topographic features more generally, and whether such regular tidal motions contribute to enhanced productivity locally.