C-SALT: An investigation of the thermohaline staircase in the western tropical North Atlantic

Schmitt, Raymond W.; Perkins, Henry; Boyd, Janice D.; Stalcup, Marvel C.

doi:10.1016/0198-0149(87)90014-8

Cited by 161 publications

(157 citation statements)

References 18 publications

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“…The anticorrelation of the step heights withR is particularly conspicuous for layers within the same staircase (see, for example, table 1 in Zodiatis & Gasparini 1996) but can also be noticed by comparing the different staircases (Schmitt 1981). The strikingly uniform apparent flux convergence ratio noted by Schmitt et al (1987) may also be directly related to the predicted uniformity of γ in the fully equilibrated staircases. However, more measurements and data analysis focusing on equilibrium balances would be needed to prove unequivocally that the predicted dynamics is realized in oceanic conditions.…”

Section: Discussionmentioning

confidence: 83%

What determines the thickness of layers in a thermohaline staircase?

Radko¹

2005

J. Fluid Mech.

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A simple theory is developed for the equilibrium height of steps in a thermohaline staircase. The model is based on a linear stability analysis for a series of salt-finger interfaces, which reveals a tendency for the staircase to evolve in time until the characteristic thickness of layers reaches a critical value (H 0 ). Relatively thin layers successively merge as a result of the parametric variation of the heat/salt flux ratio (γ ), but these mergers cease when the thickness of layers exceeds H 0 . The equilibration of thick steps in our model is caused by the slight inhomogeneity of the convecting layers which has a stabilizing effect on the staircase. The instability theory is successfully tested against fully nonlinear numerical simulations and is qualitatively consistent with oceanic observations.

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Section: Discussionmentioning

confidence: 83%

What determines the thickness of layers in a thermohaline staircase?

Radko¹

2005

J. Fluid Mech.

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“…Here, we present a seismic transect from an area previously shown to be prone to salt-finger staircase development, in the western tropical North Atlantic near the Lesser Antilles (Schmitt et al, 1987). Seismic data are supplemented by oceanographic measurements of hydrography, currents and microstructure, and synthetic modelling.…”

Section: Introductionmentioning

confidence: 99%

“…Studies have suggested that salt fingering can greatly affect the vertical transport of heat and salt in the thermocline and play a significant role in maintaining the global thermohaline stratification (Schmitt et al, 1987(Schmitt et al, , 2005. Salt fingering may play a role in the tightness and shape of the mean temperature-salinity relation in the central waters of subtropical gyres (Schmitt, 1981(Schmitt, , 1990.…”

Section: Introductionmentioning

confidence: 99%

Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

et al. 2010

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Abstract. Multichannel seismic data acquired in the Lesser Antilles in the western tropical North Atlantic indicate that the seismic reflection method has imaged an oceanic thermohaline staircase. Synthetic acoustic modeling using measured density and sound speed profiles corroborates inferences from the seismic data. In a small portion of the seismic image, laterally coherent, uniform layers are present at depths ranging from 550-700 m and have a separation of ∼ 20 m, with thicknesses increasing with depth. The reflection coefficient, a measure of the acoustic impedance contrasts across these reflective interfaces, is one order of magnitude greater than background noise. Hydrography sampled in previous surveys suggests that the layers are a permanent feature of the region. Spectral analysis of layer horizons in the thermohaline staircase indicates that internal wave activity is anomalously low, suggesting weak internal waveinduced turbulence. Results from two independent measurements, the application of a finescale parameterization to observed high-resolution velocity profiles and direct measurements of turbulent dissipation rate, confirm these low levels of turbulence. The lack of internal wave-induced turbulence may allow for the maintenance of the staircase or may be due to suppression by the double-diffusive convection within the staircase. Our observations show the potential for seismic oceanography to contribute to an improved understanding of occurrence rates and the geographical distribution of thermohaline staircases, and should thereby improve estimates of vertical mixing rates ascribable to salt fingering in the global ocean.

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“…This up-gradient flux of density has been shown to form and maintain a thermohaline staircase, in which a series of well-mixed layers are separated by sharp interfaces Stern and Turner 1969. Such staircases have been observed at the Mediterranean outflow, the Tyrrhenian Sea, and in the tropical Atlantic near Barbados Schmitt et al, 1987. The existence of a thermohaline staircase is taken to be a strong indicator of salt-finger mixing.…”

Section: Introductionmentioning

confidence: 99%

“…The work presented here will rely on observations of microscale dissipation ob tained from the free falling High Resolution Profiler HRP, Schmitt et al, 1987, as a means of assessing the diapycnal fluxes occurring in the thermocline at the NATRE site. A previous comparison of microstructure-derived diffusivities Toole et al, 1994 and tracer-derived diffusivities Ledwell et al, 1993 has indicated general agreement.…”

Section: Introductionmentioning

confidence: 99%

Diapycnal advection by double diffusion and turbulence in the ocean

Laurent¹

1999

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Observations of diapycnal mixing rates are examined and related to diapycnal advection for both double-diffusive and turbulent regimes.The role of double-diffusive mixing at the site of the North Atlantic Tracer Release Experiment is considered. The strength of salt-finger mixing is analyzed in terms of the stability parameters for shear and double-diffusive convection, and a nondi mensional ratio of the thermal and energy dissipation rates. While the model for turbulence describes most dissipation occurring in high shear, dissipation in low shear is better described by the salt-finger model, and a method for estimating the salt-finger enhancement of the diapycnal haline diffusivity over the thermal diffusivity is proposed. Best agreement between tracer-inferred mixing rates and microstructure based estimates is achieved when the salt-finger enhancement of haline flux is taken into account.The role of turbulence occurring above rough bathymetry in the abyssal Brazil Basin is also considered. The mixing levels along sloping bathymetry exceed the levels observed on ridge crests and canyon floors. Additionally, mixing levels modulate in phase with the spring-neap tidal cycle. A model of the dissipation rate is derived and used to specify the turbulent mixing rate and constrain the diapycnal advection in an inverse model for the steady circulation. The inverse model solution reveals the presence of a secondary circulation with zonal character.These results suggest that mixing in abyssal canyons plays an important role in the mass budget of Antarctic Bottom Water.Thesis Supervisor:

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C-SALT: An investigation of the thermohaline staircase in the western tropical North Atlantic

Cited by 161 publications

References 18 publications

What determines the thickness of layers in a thermohaline staircase?

What determines the thickness of layers in a thermohaline staircase?

Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

Diapycnal advection by double diffusion and turbulence in the ocean

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