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This study investigates three-dimensional semidiurnal internal tide (IT) energetics in the vicinity of La Jolla Canyon, a steep shelf submarine canyon off the Southern California coast, with the Stanford Unstructured Nonhydrostatic Terrain-Following Adaptive Navier–Stokes Simulator (SUNTANS) numerical simulator. Numerical simulations show vertical structure and temporal phasing consistent with detailed field observations. ITs induce large (approximately 34 m from peak to peak) isotherm displacements and net onshore IT energy flux up to 200 W m−1. Although the net IT energy flux is onshore, the steep supercritical slope around the canyon results in strong reflection. The model provides the full life span of internal tides around the canyon, including internal tide generation, propagation, and dissipation. ITs propagate into the canyon from the south and are reflected back toward offshore from the canyon's north side. In the inner part of the canyon, elevated mixing occurs in the middle layer due to an interaction between incident mode-1 ITs and reflected higher-mode ITs. The magnitude of IT flux, generation, and dissipation on the south side of the canyon are higher than those on the north side. An interference pattern in horizontal kinetic energy and available potential energy with a scale of approximately 20–50 km arises due to low-mode wave reflections. Our results provide new insight into IT dynamics associated with a small-scale canyon topography. Significance Statement: Internal waves play an important role in ocean circulations and ecosystems. In particular, internal waves with frequencies of tides, known as internal tides, strongly enhance energy, heat, and mass transport in coastal oceans. This study presents internal tide dynamics in La Jolla Canyon, California, using a high-resolution numerical model. Model results show energy convergence in the canyon leading to internal tide energy dissipation and mixing. Some parts of internal tide energy reflect back offshore resulting in standing internal waves off California. This study provides new insights into internal tide dynamics and energy budgets in submarine canyons. [ABSTRACT FROM AUTHOR]

Space- and time-continuous seafloor temperature observations captured the three-dimensional structure of shoaling nonlinear internal waves (NLIWs) off of La Jolla, California. NLIWs were tracked for hundreds of meters in the cross- and along-shelf directions using a fiber optic distributed temperature sensing (DTS) seafloor array, complemented by an ocean-wave-powered vertical profiling mooring. Trains of propagating cold-water pulses were observed on the DTS array inshore of the location of polarity transition predicted by weakly nonlinear internal wave theory. The subsequent evolution of the temperature signatures during shoaling was consistent with that of strongly nonlinear internal waves with a large Froude number, highlighting their potential to impact property exchange. Unexpectedly, individual NLIWs were trailed by a coherent, small-scale pattern of seabed temperature variability as they moved across the mid- and inner shelf. A kinematic model was used to demonstrate that the observed patterns were consistent with a transverse instability with an along-crest wavelength of ∼10 m—a distance comparable to the cross-crest width of the wave core—and with an inferred amplitude of several meters. The signature of this instability is consistent with the span-wise vortical circulations generated in three-dimensional direct numerical simulations of shoaling and breaking nonlinear internal waves. The coupling between the small-scale transverse wave wake and turbulent wave core may have an important impact on mass, momentum, and tracer redistribution in the coastal ocean. Significance Statement: Internal waves permeate the ocean and atmosphere. Their transport of energy and momentum plays a central role in the ocean as a physical system and mediates critical biogeochemical property exchange. In the coastal ocean, internal waves fuel the local ecosystem by redistributing nutrients and shape the local geomorphology by resuspending and transporting sediment. Despite these important impacts, a detailed understanding of nonlinear internal wave evolution in shallow water remains an elusive goal, limited by the difficulty of observing the process in action. Here we describe a transformative observational approach to track internal waves through shoaling to dissipation, combining fiber optic distributed temperature sensing and ocean-wave-powered vertical profiling to track individual waves continuously in the cross- and along-shelf direction. The waves arise from the locally energetic internal tide and undergo rapid nonlinear transformation in the shallow waters of the inner shelf. Our measurements provide the first observational evidence that after evolving into highly nonlinear waves of elevation, the waves develop a trailing, wake-like, three-dimensional instability. This instability resembles the vortical coherent structures generated in high resolution numerical simulations of internal wave shoaling, previous observations of related phenomena in the atmosphere, and in breaking surface gravity waves. The observed transverse structure has an along-crest wavelength of only ∼10 m, making it nearly invisible to traditional ocean sampling techniques. The generation of coherent vortical structures during internal wave shoaling may have a profound influence on the exchange of energy, nutrients, and sediments in coastal oceans and lakes globally. [ABSTRACT FROM AUTHOR]