Collaborative Research: River plume-cape interaction - Plume separation from the coastal wall, vorticity generation and fresh water retention

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This project will examine the interaction of a stratified coastal plume with a cape, using a combined observational and modeling approach. High-resolution shipboard surveys and moored instrumentation near Point Reyes, CA, will measure the circulation and evolution of the San Francisco Bay Plume under a range of wind and river discharge conditions. Combined numerical model simulations and observations will quantify the dynamical balances and residence times of the Plume downstream of the Cape. Idealized simulations will permit expansion of results across parameter space, to understand both the controlling dynamics and conditions affecting plume separation and retention times of stratified plumes in the lee of capes in the coastal ocean. Coastal plumes are a key component of shelf circulation, and important conduits for transport of pollutants, nutrients, water masses and the organic carbon they contain. Understanding the factors influencing plume separation and retention times will contribute to understanding fates of such societally important ocean constituents.Complex coastal geometries, such as capes and submarine banks, can lead to significant hydrodynamic disturbances of buoyant coastal flows. Such plumes are key components of shelf circulation and coastal ocean biogeochemistry and marine ecosystems, so their dynamics and fate are critical to understand. This project will quantify the interaction between the San Francisco Bay Plume in the vicinity of Point Reyes, CA, under a range of wind and river discharge conditions, using shipboard, moored, and drifter field observations, combined with realistic and idealized numerical modeling studies. The main objectives are to: (1) obtain detailed measurements of plume hydrography, along- and cross-stream velocities and transports near a cape, under a range of river discharge and wind-forcing conditions, (2) identify the conditions for plume separation from the coast and eddy generation in the lee of a cape, (3) quantify the retention time scales downstream of the cape associated with the generated eddies, and (4) investigate the dominant momentum balances that control far-field dynamics as the plume interacts with a cape. Although plumes encompass a small area of the ocean surface, they are the boundary condition for larger scale shelf circulation, and thus their evolution is critical to understand and represent realistically in models. This project will result in better understanding of the fate and transport of pollutants, nutrients and water masses in the ocean, contribute observational datasets, models, and analysis tools to the science community, and will provide critical research capacity for two early career scientists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.