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Lawrence J. Pratt. Dell, Rebecca Walsh Woods Hole Oceanographic Institution. Joint Program in Oceanography/Applied Ocean Science and Engineering Woods Hole Oceanographic Institution Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences 2010-10-29T18:03:59Z 2010-10-29T18:03:59Z 2010 2010 http://hdl.handle.net/1721.1/59657 645263846 Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010. Includes bibliographical references (p. 54-56). This paper begins to explore a previously neglected mechanism for abyssal ocean mixing using bottom boundary layer dynamics. Abyssal mixing and the associated upward buoyancy fluxes are necessary to balance the sinking of dense waters at high latitudes and to close the global overturning circulation. Previous studies have concentrated on the hypothesis that the primary mechanism for this mixing is breaking internal waves generated by tidal flows over rough topography. However, intriguing observations, particularly from the Brazil Basin Tracer Release Experiment, suggest that mixing in the flank canyons of the Mid-Atlantic Ridge generated when strong mean flows interact with the many sills and constrictions within the canyons may represent a dynamically important amount of abyssal mixing. The energy pathways and mechanisms of this mixing are much less clear than in the case of breaking internal waves. This study attempts to clarify this by suggesting an analogy with an idealized diffusive boundary layer over a sloping bottom. This boundary layer is characterized by up-slope flows powered by the buoyancy flux in the fluid far from the boundary. Here we explore the energy budget of the boundary layer, and find that the diffusive boundary layer provides flows that are generally consistent with those observed in submarine canyons. In addition, we derive the vertical velocity in the far-field fluid, analogous to an Ekman pumping velocity, that these boundary layers can induce when the bottom slope is not constant. Finally, we present both theoretical and numerical models of exchange flows between the bottom boundary and the far-field flow when the bottom slope is not constant. These exchange flows provide a mechanism by which boundary-driven mixing can affect the overall stratification and buoyancy fluxes of the basin interior. by Rebecca Walsh Dell. S.M. 56 p. eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Joint Program in Oceanography/Applied Ocean Science and Engineering. Earth, Atmospheric, and Planetary Sciences. Woods Hole Oceanographic Institution. Oceanic mixing Abyssal zone Abyssal mixing from bottom boundary effects in Mid-Atlantic Ridge flank canyons Thesis application/pdf false Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="17a14c32-8362-479f-956a-8b1723a52c49"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Abyssal mixing from bottom boundary effects in Mid-Atlantic Ridge flank canyons</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2010</PublicationDate> <Authors> <Author> <DisplayName>Dell, Rebecca Walsh</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Joint Program in Oceanography/Applied Ocean Science and Engineering.</Keyword> <Keyword>Earth, Atmospheric, and Planetary Sciences.</Keyword> <Keyword>Woods Hole Oceanographic Institution.</Keyword> <Abstract>This paper begins to explore a previously neglected mechanism for abyssal ocean mixing using bottom boundary layer dynamics. Abyssal mixing and the associated upward buoyancy fluxes are necessary to balance the sinking of dense waters at high latitudes and to close the global overturning circulation. Previous studies have concentrated on the hypothesis that the primary mechanism for this mixing is breaking internal waves generated by tidal flows over rough topography. However, intriguing observations, particularly from the Brazil Basin Tracer Release Experiment, suggest that mixing in the flank canyons of the Mid-Atlantic Ridge generated when strong mean flows interact with the many sills and constrictions within the canyons may represent a dynamically important amount of abyssal mixing. The energy pathways and mechanisms of this mixing are much less clear than in the case of breaking internal waves. This study attempts to clarify this by suggesting an analogy with an idealized diffusive boundary layer over a sloping bottom. This boundary layer is characterized by up-slope flows powered by the buoyancy flux in the fluid far from the boundary. Here we explore the energy budget of the boundary layer, and find that the diffusive boundary layer provides flows that are generally consistent with those observed in submarine canyons. In addition, we derive the vertical velocity in the far-field fluid, analogous to an Ekman pumping velocity, that these boundary layers can induce when the bottom slope is not constant. Finally, we present both theoretical and numerical models of exchange flows between the bottom boundary and the far-field flow when the bottom slope is not constant. These exchange flows provide a mechanism by which boundary-driven mixing can affect the overall stratification and buoyancy fluxes of the basin interior.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>