Frontogenesis and Frontal Progression of a Trapping-Generated Estuarine Convergence Front and Its Influence on Mixing and Stratification |
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| Authors: | Sarah N Giddings Derek A Fong Stephen G Monismith C Chris Chickadel Kathleen A Edwards William J Plant Bing Wang Oliver B Fringer Alexander R Horner-Devine and Andrew T Jessup |
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| Institution: | (1) School of Oceanography, University of Washington, OCN Box 357940, Seattle, WA 98195-7940, USA;(2) Department Civil and Environmental Engineering, Stanford University, 473 Via Ortega St., Stanford, CA 94305-4020, USA;(3) Applied Physics Laboratory, University of Washington, 1013 NE 40th St., Seattle, WA 98105, USA;(4) Ocean Power Technologies, 1590 Reed Road, Pennington, NJ 08534, USA;(5) Department Civil and Environmental Engineering, University of Washington, 201 More Hall, Box 352700, Seattle, WA 98195-2700, USA |
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| Abstract: | Estuarine fronts are well known to influence transport of waterborne constituents such as phytoplankton and sediment, yet
due to their ephemeral nature, capturing the physical driving mechanisms and their influence on stratification and mixing
is difficult. We investigate a repetitive estuarine frontal feature in the Snohomish River Estuary that results from complex
bathymetric shoal/channel interactions. In particular, we highlight a trapping mechanism by which mid-density water trapped
over intertidal mudflats converges with dense water in the main channel forming a sharp front. The frontal density interface
is maintained via convergent transverse circulation driven by the competition of lateral baroclinic and centrifugal forcing.
The frontal presence and propagation give rise to spatial and temporal variations in stratification and vertical mixing. Importantly,
this front leads to enhanced stratification and suppressed vertical mixing at the end of the large flood tide, in contrast
to what is found in many estuarine systems. The observed mechanism fits within the broader context of frontogenesis mechanisms
in which varying bathymetry drives lateral convergence and baroclinic forcing. We expect similar trapping-generated fronts
may occur in a wide variety of estuaries with shoal/channel morphology and/or braided channels and will similarly influence
stratification, mixing, and transport. |
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