The bottom boundary layer of the deep ocean

Armi, Laurence; Millard, Robert C.

doi:10.1029/jc081i027p04983

Cited by 155 publications

(75 citation statements)

References 19 publications

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“…This is also true in the benthic boundary layer where a well-mixed boundary layer of variable thickness is nearly ubiquitous. [28][29][30] That the dominant region of turbulence production is relatively unaffected by stratification is why the gradient Richardson number, often used in parametrizations of stratified turbulence, is less useful in the present study. Indeed, as has been shown, many turbulence and mixing quantities, when plotted as a function of Ri g , do not show collapse between cases to a universal dependence on Ri g observed in previous studies of flow with vertical shear.…”

Section: -16mentioning

confidence: 64%

Large eddy simulation of stably stratified open channel flow

2005

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Large eddy simulation has been used to study flow in an open channel with stable stratification imposed at the free surface by a constant heat flux and an adiabatic bottom wall. This leads to a stable pycnocline overlying a well-mixed turbulent region near the bottom wall. The results are contrasted with studies in which the bottom heat flux is nonzero, a difference analogous to that between oceanic and atmospheric boundary layers. Increasing the friction Richardson number, a measure of the relative importance of the imposed surface stratification with respect to wall-generated turbulence, leads to a stronger, thicker pycnocline which eventually limits the impact of wall-generated turbulence on the free surface. Increasing stratification also leads to an increase in the pressure-driven mean streamwise velocity and a concomitant decrease in the skin friction coefficient, which is, however, smaller than in the previous channel flow studies where the bottom buoyancy flux was nonzero. It is found that the turbulence in any given region of the flow can be classified into three regimes ͑unstratified, buoyancy-affected, and buoyancy-dominated͒ based on the magnitude of the Ozmidov length scale relative to a vertical length characterizing the large scales of turbulence and to the Kolmogorov scale. Since stratification does not strongly influence the near-wall turbulent production in the present configuration, the behavior of the buoyancy flux, turbulent Prandtl number, and mixing efficiency is qualitatively different from that seen in stratified shear layers and in channel flow with fixed temperature walls, and, furthermore, collapse of quantities as a function of gradient Richardson number is not observed. The vertical Froude number is a better measure of stratified turbulence in the upper portion of the channel where buoyancy, by providing a potential energy barrier, primarily affects the transport of turbulent patches generated at the bottom wall. The characteristics of free-surface turbulence including the kinetic energy budget and pressure-strain correlations are examined and found to depend strongly on the surface stratification.

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Section: -16mentioning

confidence: 64%

Large eddy simulation of stably stratified open channel flow

2005

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“…rep.;Harvey and Patzert 1976). Temperature profiles indicated weak stratification in the bottom 200 m and no obviously mixed benthic boundary layer (such as those described on the Hatteras abyssal plain by Armi and Millard 1976) could be detected. Table 1. Comparison between boundary layer flows in the tropical North Pacific study site and the laboratory flumes.…”

Section: Field Sitementioning

confidence: 99%

“…The thickness of a deep-sea boundary layer scales with inertial forces and can be estimated from the equation (Armi and Millard 1976) Bottom roughness can be estimated from the height (h) and areal cover (X) of "roughness elements" on a surface (Lettau 1969):…”

Section: Field Sitementioning

confidence: 99%

Vertical distributions of the epifauna on manganese nodules: Implications for settlement and feeding

Mullineaux

1989

Limnology & Oceanography

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Over 65% of the sessile organisms living on manganese nodules from the tropical North Pacific belong to taxa whose abundances are related to vertical position on the nodule. The nodule surface texture and boundary layer flow environment, two factors that also vary vertically, were investigated to determine whether they could account for the observed faunal distributions. The surface texture of nodules from the tropical Pacific is generally rough and knobby at the nodule base and smooth near the summit. Twenty-five taxa, including 68% of the total individuals, were found in significantly different abundances between the rough and smooth surfaces of 34 nodules. These distributions may be due to larval responses to surface texture and can account for much of the observed vertical zonation of the fauna. Boundary layer flows over nodules were characterized from laboratory flume studies and field observations. In flows at the field site, it is expected that mean boundary shear stress and horizontal flux of particles (food or larvae) will increase from the nodule base to the summit, while particle contact rate and deposition will decrease. The observations that suspension feeders persist near the nodule summit and deposit feeders concentrate near the base suggest that vertical distributions of some taxa may be determined by adult feeding requirements. Individuals of most taxa are relatively scarce at the nodule base, indicating that their larvae are not colonizing where they accumulate passively. High abundances of matlike agglutinated foraminifers (of unknown feeding type) at the nodule summit may be due to larval responses to the relatively'higher shear stresses. --

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“…In fact , Armi [1977] has pointed out that within the boundary mixed layer a nd above the Ekman layer sca le, very littl e is known of the turbulence. We also ass ume th at the horizontal or alon g-isopycn al exchange is rapid.…”

Section: Mixing-ad Vec Tion Model Is Illustrated Inmentioning

confidence: 99%

Some evidence for boundary mixing in the deep Ocean

Armi¹

1978

J. Geophys. Res

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263

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Profiles of salinity and potential temperature in the deep ocean are presented which suggest the characteristic signature of two complementary mixing processes: vertical mixing within ∼50‐m‐thick layers at boundaries and topographic features and lateral advection and eventual smearing of these mixed layers along iopycnal surfaces. The combined effect of these two processes is often parametrically disguised as a vertical eddy diffusivity in one‐dimensional models. An estimate shows that the two processes can account for all the vertical mixing in the deep ocean without any vertical diffusion in the interior.

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The bottom boundary layer of the deep ocean

Cited by 155 publications

References 19 publications

Large eddy simulation of stably stratified open channel flow

Large eddy simulation of stably stratified open channel flow

Vertical distributions of the epifauna on manganese nodules: Implications for settlement and feeding

Some evidence for boundary mixing in the deep Ocean

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