Nonlinear Internal Waves on the Inner Continental Shelf: Their Dynamics and Associated Cross-Shelf Fluxes

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ABSTRACTOCE-0424742In many coastal regions large amplitude, high-frequency internal waves and internal tidal bores have been observed to propagate onshore. Because of their large amplitude, these shoaling waves carry energy from their generation regions towards the coast, and transport mass and buoyancy between the outer and inner continental shelf. Field observations suggest that these waves may be critical for transporting larval stage benthic organisms from the continental shelf back to nearshore regions, where they can settle at appropriate habitats. The waves may also significantly contribute to the cross-shore transport and dispersion of nutrients and pollutants from sewage outfalls. In some regions of the coastal ocean, particularly where winds and upwelling are weak, the cross-shore transport of momentum and buoyancy due to nonlinear internal waves may be a dominant term in the inner shelf momentum and buoyancy budgets. While field evidence suggests that the importance of nonlinear internal waves on the inner shelf are compelling, detailed investigations of the dynamics of these waves and their associated fluxes are lacking and have yet to be quantified. In this project, a researcher from the Woods Hole Oceanographic Institution will examine the cross-shore momentum balance of shoaling and nonlinear internal waves, as well as quantify the fluxes of mass, buoyancy, and the Lagrangian transports associated with these waves. In addition to the field observations that were collected in the summer and fall of 1996 and 1997 off of Mission Beach, California, the Principle Investigator will utilize a two-dimensional, rotating, nonlinear, non-hydrostatic model for his investigation. The numerical model will be run using a domain with the same cross-shore geometry as that of the field observations and will be forced within the internal wave field observed at the offshore mooring site. To assess the ecological importance of nonlinear internal waves, the cross-shore transport of plankton through internal wave activity will be quantified and compared to other transport mechanisms (e.g, upwelling relaxation or coastal trapped waves). In addition, the feedback between nonlinear shoaling, breaking internal waves, and the inner shelf density field will also be quantified to determine their mechanistic relevancy to the inner shelf momentum and buoyancy budgets. Broader Impacts: The results gathered from this project will not only yield a better understanding of the fate of larvae and nutrients along the coast, but also clarify the fate of pollutants from rain runoff in populated areas. Because of this project's applicability to the design of sewage outfalls, a report of the conclusions from this study will be presented to the City of San Diego Metropolitan Wastewater Department, who operates a sewage outfall facility off of Pt. Loma, just south of where these field observations were made.