Intensification and impact of wave-breaking in river plumes

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Fronts form barriers that limit the exchange of nutrients and organisms between different water masses in the ocean. This study will investigate if wave breaking can intensify mixing at fronts between an expanding fresh water river plume and the ambient salt water offshore. The work will also contribute to the general understanding of wave-breaking and near-surface turbulence, which influence a myriad processes in the ocean. The project will support one graduate student and several outreach efforts which include maintaining a research blog and producing a video segment which will be hosted by the Applied Physics Laboratory/University of Washington website.This project will use a novel wave-turbulence measurement platform to quantify the transformation of wave energy as it passes through a river plume front and interior, as well as the impact of wave-breaking turbulence on the dynamics and mixing of the plume. The overarching hypothesis is that plume velocity gradients can intensify wave breaking, converting wave energy to turbulence, and significantly increasing plume mixing in systems where the wave scales match the vertical plume scale. The plan is to test this hypothesis by pursuing the following three specific objectives using new and existing field data: 1) quantify the loss of wave energy via breaking at fronts and within river plumes, 2) quantify the generation of near-surface turbulence during wave breaking and the vertical structure of this turbulence, and 3) assess the impact of wave breaking turbulence on mixing in river plumes. Measurements of waves, near-surface turbulence, and buoyancy flux will be done in the moderate-sized Fraser River plume (British Columbia, Canada) and the smaller-sized Elwha River plume (Washington, USA) under a range of wave conditions. Results from these measurements will be compared with existing wave and turbulence data from the much larger Columbia River plume to determine how wave-turbulence dynamics are influenced by frontal strength in different systems. The impact of this process on mixing will be assessed using drifter-based salt budgets as well as analysis of more than a decade of ferry transect data through the Fraser River plume