Ice‐Tethered Profiler observations of the double‐diffusive staircase in the Canada Basin thermocline

Timmermans, Mary‐Louise; Toole, John M.; Krishfield, Richard A.; Winsor, Peter

doi:10.1029/2008jc004829

Cited by 160 publications

(319 citation statements)

References 42 publications

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“…Furthermore, the field observations of Padman & Dillon (1987) and Timmermans et al (2008) have shown a close agreement between F mol T and the F T predicted by different laboratorybased flux laws. However, we are not aware of any study that has definitively shown the fluxes to be molecular, with the exception of the experiments of Shirtcliffe (1973) using a salt-sugar interface (τ ≈ 0.33).…”

Section: Simulations Of a Double-diffusive Interfacesupporting

confidence: 60%

Simulations of a double-diffusive interface in the diffusive convection regime

2012

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Three-dimensional direct numerical simulations are performed that give us an in-depth account of the evolution and structure of the double-diffusive interface. We examine the diffusive convection regime, which, in the oceanographically relevant case, consists of relatively cold fresh water above warm salty water. A 'double-boundary-layer' structure is found in all of the simulations, in which the temperature (T) interface has a greater thickness than the salinity (S) interface. Therefore, thin gravitationally unstable boundary layers are maintained at the edges of the diffusive interface. The TS-interface thickness ratio is found to scale with the diffusivity ratio in a consistent manner once the shear across the boundary layers is accounted for. The turbulence present in the mixed layers is not able to penetrate the stable stratification of the interface core, and the TS-fluxes through the core are given by their molecular diffusion values. Interface growth in time is found to be determined by molecular diffusion of the S-interface, in agreement with a previous theory. The stability of the boundary layers is also considered, where we find boundary layer Rayleigh numbers that are an order of magnitude lower than previously assumed.

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Section: Simulations Of a Double-diffusive Interfacesupporting

confidence: 60%

Simulations of a double-diffusive interface in the diffusive convection regime

2012

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“…The Arctic Ocean is a quiescent environment with turbulence levels close to the limits of measurement (RainCorresponding author: Ilker FER, ilker.fer@gfi.uib.no ville and Winsor, 2008). In the absence of enhanced levels of mixing due to episodic shear events or mesoscale eddies, diffusive layer fluxes dominate over turbulent fluxes (Padman and Dillon, 1989;Timmermans et al, 2008). Consistent with a quiescent Arctic interior, recent numerical studies suggest that the observed AW layer circulation in the Arctic Ocean requires low vertical mixing (Zhang and Steele, 2007).…”

Section: Introductionmentioning

confidence: 87%

Weak Vertical Diffusion Allows Maintenance of Cold Halocline in the Central Arctic

Fer

2009

Atmospheric and Oceanic Science Letters

119

131

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In spring preceding the record minimum summer ice cover detailed microstructure measurements were made from drifting pack ice in the Arctic Ocean, 110 km from the North Pole. Profiles of hydrography, shear, and temperature microstructure collected in the upper water column covering the core of the Atlantic Water are analyzed to determine the diapycnal eddy diffusivity, the eddy diffusivity for heat, and the turbulent flux of heat. Turbulence in the bulk of the cold halocline layer was not strong enough to generate significant buoyancy flux and mixing. Resulting turbulent heat flux across the upper cold halocline was not significantly different than zero. The results show that the low levels of eddy diffusivity in the upper cold halocline lead to small vertical turbulent transport of heat, thereby allowing the maintenance of the cold halocline in the central Arctic.

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“…Estimating the vertical fluxes through such staircases is important, in particular in the Arctic Ocean, where double-diffusive heat transport to the overlying ice needs to be quantified [Timmermans et al, 2008;Turner, 2010].…”

Section: Introductionmentioning

confidence: 99%

Double‐diffusive interfaces in Lake Kivu reproduced by direct numerical simulations

Sommer

Carpenter

Wüest

2014

Geophysical Research Letters

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Double diffusion transforms uniform background gradients of temperature and salinity into "staircases" of homogeneous mixed layers that are separated by high-gradient interfaces. Direct numerical simulations (DNS) and microstructure measurements are two independent methods of estimating double-diffusive fluxes. By performing DNS under similar conditions as found in our measurements in Lake Kivu, we are able to compare results from both methods for the first time. We find that (i) the DNS reproduces the measured interface thicknesses of in situ microstructure profiles, (ii) molecular heat fluxes through interfaces capture the total vertical heat fluxes for density ratios larger than three, and (iii) the commonly used heat flux parameterization underestimates the total fluxes by a factor of 1.3 to 2.2.

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Ice‐Tethered Profiler observations of the double‐diffusive staircase in the Canada Basin thermocline

Cited by 160 publications

References 42 publications

Simulations of a double-diffusive interface in the diffusive convection regime

Simulations of a double-diffusive interface in the diffusive convection regime

Weak Vertical Diffusion Allows Maintenance of Cold Halocline in the Central Arctic

Double‐diffusive interfaces in Lake Kivu reproduced by direct numerical simulations

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