Collaborative Research: The Role of Coastal Fronts in Mixing and Ventilating Coastal Waters

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National Science Foundation
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A state-of-the-art suite of instrumented autonomous and drifting platforms will be used to resolve fine- scale dynamics that lead to the enhancement of mixing and vertical exchange in the vicinity of coastal fronts. The interaction between surface wave breaking, bubble-entrainment, and downwelling convergence are of particular focus, with our primary goal being to investigate the specific nature and transiency of turbulent exchange at these locations. The proposed work builds on recent results using SWIFT drifters as well as a REMUS 600 autonomous underwater vehicle to measure upper ocean turbulent dissipation rates. Detailed measurements of turbulent energetics and Reynolds stresses will provide a transformative view of exchange processes at episodic and transient frontal features. This will be linked to dynamics driving frontogenesis through control volume analyses and estimates of topographic form drag. Through the collection of comprehensive in-situ measurements proposed here, the role(s) of surface fronts in ventilating and mixing coastal and estuarine waters can be quantitatively characterized.

Intellectual Merit:

This proposed work will advance our understanding of vertical exchange in the dynamic surface ocean in regions where standard boundary layer models break down: surface fronts. Interactions between strong stratification, convergence, and enhanced vertical fluxes at submesoscale fronts remain poorly understood processes that have important and immediate implications for gas and energy exchange within the world’s oceans. In coastal margins, where natural and built environments often interact, in situ measurements of turbulent mixing driven by the presence of ocean fronts can improve estimates of exchange rates that determine a system’s susceptibility to acidification and hypoxia, primary production, and transport of material. The detailed observations proposed here will yield new insights into parameterizing air-sea fluxes at ocean fronts and other convergent features in the upper ocean including those generated by Langmuir turbulence.

Broader Impacts:

This study will improve our ability to predict and manage coastal ocean acidification and hypoxia, as well as enable new lines of inquiry into upper ocean exchange processes. The project will also develop the career of a young scientist, who will transition to be the lead principal investigator of this proposed study and develop skills to lead future work. Outreach efforts will include participation in the annual University of Washington Discovery Days event, which draws over 10,000 students from regional K-12 schools to visit the campus and learn about current research. We will foster student participation at multiple levels by pursuing undergraduate research opportunities through the NSF REU program as well as promote involvement of graduate and undergraduate students within the Department of Civil and Environmental Engineering at the University of Washington. Finally, summer support is included for one graduate student at UCSB.