Mixing at the ocean's bottom boundary

Polzin, Kurt L.; McDougall, Trevor J.

doi:10.1016/b978-0-12-821512-8.00014-1

Cited by 16 publications

(22 citation statements)

References 132 publications

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“…The fallacy [42] underlying these [50] upwelling arguments may originate in the fact that the no-flux bottom boundary condition controls the stratification only on scales smaller than the log-layer [29,64], rather than the O(100) m envisioned by those authors [50,62,63]. Clearly, further work needs to be done.…”

Section: Diapycnal Advectionmentioning

confidence: 99%

“…As with the turbulent kinetic energy equation, the situation is not so clear in the presence of a boundary. A no flux bottom boundary condition requires mean isopycnals to be normal to topography and the boundary region can host significant lateral production in combination with vertical production [42].…”

Section: The Turbulent Paradigmmentioning

confidence: 99%

“…The logic behind these arguments implicitly assumes that horizontal and vertical temperature fluxes have a similar order of magnitude and that balances in the temperature (buoyancy) variance Equation ( 9) are local (i.e., the nonlinear transport terms can be neglected) [42]. With such assumptions, the no-flux bottom boundary condition can be reduced to a requirement that the vertical buoyancy flux tends toward zero as the bottom is approached [50].…”

Section: Diapycnal Advectionmentioning

confidence: 99%

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Moored Flux and Dissipation Estimates from the Northern Deepwater Gulf of Mexico

Polzin

Wang

et al. 2021

Fluids

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Results from a pilot program to assess boundary mixing processes along the northern continental slope of the Gulf of Mexico are presented. We report a novel attempt to utilize a turbulence flux sensor on a conventional mooring. These data document many of the features expected of a stratified Ekman layer: a buoyancy anomaly over a height less than that of the unstratified Ekman layer and an enhanced turning of the velocity vector with depth. Turbulent stress estimates have an appropriate magnitude and are aligned with the near-bottom velocity vector. However, the Ekman layer is time dependent on inertial-diurnal time scales. Cross slope momentum and temperature fluxes have significant contributions from this frequency band. Collocated turbulent kinetic energy dissipation and temperature variance dissipation estimates imply a dissipation ratio of 0.14 that is not sensibly different from canonical values for shear instability (0.2). This mixing signature is associated with production in the internal wave band rather than frequencies associated with turbulent shear production. Our results reveal that the expectation of a quasi-stationary response to quasi-stationary forcing in the guise of eddy variability is naive and a boundary layer structure that does not support recent theoretical assumptions concerning one-dimensional models of boundary mixing.

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Section: Diapycnal Advectionmentioning

confidence: 99%

Section: The Turbulent Paradigmmentioning

confidence: 99%

Section: Diapycnal Advectionmentioning

confidence: 99%

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Moored Flux and Dissipation Estimates from the Northern Deepwater Gulf of Mexico

Polzin

Wang

et al. 2021

Fluids

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“…Since the signature of the BML is typical of a mixing process, it is accepted that the H BML forms as a result of mixing the uniformly stratified fluid, which is closely linked with active dynamic processes and topographic features (Polzin and McDougall, 2022). For example, previous observational studies have shown that the variability of the H BML was strongly associated with bottom currents (Wunsch and Hendry, 1972;Armi and Millard, 1976;Zulberti et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

Spatial-temporal characteristics of the oceanic bottom mixed layer in the South China Sea

et al. 2023

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The oceanic bottom mixed layer (BML) plays an important role in transporting mass, heat, and momentum between the ocean interior and the bottom boundary. However, the spatial-temporal characteristics of the BML in the South China Sea (SCS) is not well understood. Using 514 full-depth temperature and salinity profiles collected during the time period from 2004 to 2018 and two particularly deployed hydrographic moorings, the temporal and spatial variations of the BML have been analyzed. The results show that the BML in the SCS exhibits significant inhomogeneity, with thickness and stability varying across different regions. Specifically, the BML is relatively thin and stable over the continental shelf and deep-sea regions, while it is thicker and less stable over the northern continental slope. The mean, median, and one standard deviation values of BML thickness over the entire SCS were found to be 73 m, 56 m, and 55 m, respectively. Further analysis reveals that energetic high-frequency dynamic processes, coupled with steep bottom topography, contribute to strong tidal dissipation and vertical mixing near the bottom over the continental slope, resulting in thicker BMLs. Conversely, dynamic processes in the deep ocean are less energetic and low-frequency, the topography is relatively smooth, and tidal dissipation and bottom vertical mixing are weaker, leading to a thinner BML. These findings enhance our understanding of the BML dynamics in the SCS and other marginal seas and provide insights to improve parameterizations of physical processes in ocean models.

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“…The awareness of the unsteady state of the deep ocean is fairly recent achievement. These recent assumptions (Ferrari et al, 2016;MacKinnon et al, 2017;McDougall and Ferrari, 2017;Holmes et al, 2018;Polzin and McDougall, 2021) are shedding light on the rising need to fully understand the mechanisms that can induce instability of the deep layers with a particular look at the role that seafloor roughness and shape have in triggering bottom mixing processes (de Lavergne et al, 2016;Naveira Garabato et al, 2019;Spingys et al, 2021). Observational datasets over many decades are required to document, understand, and predict the climate system as a whole.…”

Section: Introductionmentioning

confidence: 99%

Editorial: Impact of Deep Oceanic Processes on Circulation and Climate Variability: Examples From the Mediterranean Sea and the Global Ocean

2021

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Mixing at the ocean's bottom boundary

Cited by 16 publications

References 132 publications

Moored Flux and Dissipation Estimates from the Northern Deepwater Gulf of Mexico

Moored Flux and Dissipation Estimates from the Northern Deepwater Gulf of Mexico

Spatial-temporal characteristics of the oceanic bottom mixed layer in the South China Sea

Editorial: Impact of Deep Oceanic Processes on Circulation and Climate Variability: Examples From the Mediterranean Sea and the Global Ocean

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