High mixing rates in the abyssal Southern Ocean

The variability of the turbulent kinetic energy dissipation due to internal waves is quantified using a finescale parameterization applied to the A25 Greenland-Portugal transect repeated every two years from 2002 to 2012. The internal wave velocity shear and strain are estimated for each cruise at 91 stations from full depth vertical profiles of density and velocity. . The interannual variability in the dissipation rates is remarkably small over the whole transect. A few strong dissipation rate events exceeding the uncertainty of the finescale parameterization occur at depth between the Azores-Biscay Rise and Eriador Seamount. This region is also marked by mesoscale eddying flows resulting in enhanced surface energy level and enhanced bottom velocities. Estimates of the vertical energy fluxes into the internal tide and into topographic internal waves suggest that the latter are responsible for the strong dissipation events. At Eriador Seamount, both topographic internal waves and the internal tide contribute with the same order of magnitude to the dissipation rate while around the Reykjanes Ridge the internal tide provides the bulk of the dissipation rate.

mentioning

confidence: 68%

Variability of the Turbulent Kinetic Energy Dissipation along the A25 Greenland–Portugal Transect Repeated from 2002 to 2012

Ferron

Kokoszka

Mercier

et al. 2016

“…As previously documented with other observations, the South China Sea ) and Hawaiian Ridge ) both have diffusivities as high as K ; 10 23 m 2 s 21 . Elevated diffusivities are also found south of Australia and in the Southern Ocean east of South America (Heywood et al 2002). Equatorial regions also show enhanced diffusivity, which has been linked to diurnal deep-cycle turbulence, tropical instability waves, and instabilities of the Equatorial Undercurrent (Moum et al 2009), processes that are likely confined to the upper ocean.…”

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confidence: 93%

Global Patterns of Diapycnal Mixing from Measurements of the Turbulent Dissipation Rate

Waterhouse

MacKinnon

Nash

et al. 2014

Self Cite

445

467

The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10 . The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depthintegrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.

“…High mixing rates observed or inferred to prevail in the deep Southern Ocean (Olbers and Wenzel 1989, Heywood et al 2002, Naveira Garabato et al 2004, Sloyan 2005, Kunze et al 2006 are 716 often suggested to contribute prominently to the diabatic closure of the abyssal overturning circulation (Ito andMarshall 2008, Nikurashin andFerrari 2013). However, inverse estimates and 718 model simulations generally show an increase of the maximum northward abyssal flow as AABW crosses the ACC (e.g., Lumpkin and Speer 2007, Jayne 2009, Melet et al 2014, 720…”

mentioning

confidence: 99%

On the Consumption of Antarctic Bottom Water in the Abyssal Ocean

Lavergne

Madec

Sommer

et al. 2016

Self Cite

127

149

Manuscript (non-LaTeX)Click here to download Manuscript (non-LaTeX) Full manuscript.docx ABSTRACT 24The abyssal ocean is primarily filled by cold, dense waters formed around Antarctica and 26 collectively referred to as Antarctic Bottom Water (AABW). At steady state, AABW must be consumed in the ocean interior at the same rate it is produced, but how and where this 28 consumption is achieved remains poorly understood. Here, we present estimates of abyssal water mass transformation by geothermal heating and parameterized internal wave-driven mixing. We 30 use maps of the energy input to internal waves by tidal and geostrophic motions interacting with topography combined with assumptions about the distribution of energy dissipation to evaluate