ABSTRACT

Intellectual Merit: River plume dynamics control the fate and transport of low salinity waters, nutrients, sediments and pollutants associated with river discharge. The buoyancy driven transport is modified by processes that influence circulation in coastal seas, especially atmospheric fluxes, wind stress and topographic effects. These interactions have been studied extensively, in both idealized and realistic settings. However, most previous studies have concentrated on estuarine discharges on broad or narrow continental shelves that have simple geometry near the river mouth and bottom slopes in the cross-shore direction only. Furthermore, river plume studies have often neglected the effect of ambient currents, especially slope eddies associated with boundary flows impinging on the shelf, which can potentially either trap river waters and transport them great distances away from the freshwater source or promote retention that can lead to coastal inundation and flooding.

Satellite data and numerical studies in marginal seas have revealed that topography and boundary currents, fronts and eddies in the vicinity of large freshwater discharges modify the conventional river plume behavior and alter the preferred pathways for low salinity waters and associated materials from land drainage.

The broad goal of the proposed study is to advance the understanding of river plume dynamics by examining the processes that control the transport and fate of river waters in the presence of complex topography, variable wind forcing and under the influence of outer shelf, slope and deep processes associated with a boundary current and the related eddy field. The study methodology addresses both a conceptual part and a realistic application. Process oriented experiments will be performed in a realistic model domain setting to analyze the role of topography and wind-driven currents on the evolution of the Mississippi River plume.

Recent advances in numerical studies of shelf dynamics allow the nesting of high resolution shelf models to a hierarchy of regional and large scale models that employ data assimilation, are eddy resolving and can thus enable the realistic representation of coastal to offshore interactions. Such a model will be employed in this study for a realistic test case application on the transport of waters discharged at the Mississippi River delta, one of the greatest world rivers, where a combination of complex topography and strong ambient flows are in place. Satellite products will by employed to identify prominent events of interaction between Mississippi waters and ambient shelf and deep sea flows. In-situ measurements near the shelf-break will be employed for a quantitative evaluation of model results. Numerical experiments with realistic, high frequency forcing will be executed to study characteristic events of plume/boundary current interaction in detail and analyze the mechanisms that control cross-marginal transport. Analysis of the distribution, transport and residence time of river waters based on model results and validated against unassimilated data will verify the study hypotheses and enhance the capability to predict transport pathways in complex settings.

Broader Impacts: Large river discharges, due to their high volume and high content in nutrients, sediments and pollutants, play a prominent role in fisheries, ocean health, coastal development and wetland conservation; impacts are amplified at areas subject to extreme storm conditions and hypoxia events. The potential connectivity to remote ecosystems allowed by coastal to offshore interactions has pronounced scientific and socioeconomic impacts. These associations make the study results unique for education and outreach, as they relate to problems familiar to students, young scientists and the general public. Extensive relevant activities have already been planned and they will be strengthened by ancillary projects. The PI and the research scientist are women, an under-represented group in oceanography.

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