Significance of Diapycnal Mixing Within the Atlantic Meridional Overturning Circulation

Cimoli, Laura; Mashayek, Ali; Johnson, H. L.; Marshall, David P.; Garabato, Alberto C. Naveira; Whalen, Caitlin B.; Vic, Clément; Lavergne, Casimir de; Alford, Matthew H.; MacKinnon, Jennifer A.; Talley, Lynne D.

doi:10.1029/2022av000800

Cited by 12 publications

(9 citation statements)

References 94 publications

(220 reference statements)

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“…The above consideration suggests that taking the more realistic spatially varying dissipation efficiency q into account can enhance the difference between the available energy source for tidal mixing in the upper part of the Atlantic and that in the deep Atlantic. This may further strengthen the impact of deep tidal mixing on the deep overturning circulations (Cimoli et al 2023).…”

Section: A Comparison Of E Lvs With Other Estimates Of Internal Tide ...mentioning

confidence: 88%

Sensitivity of Internal-Tide Generation to Stratification and Its Implication for Deep Overturning Circulations

Lüschow,

von Storch

2024

Journal of Physical Oceanography

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The simple scaling relation for internal-tide generation proposed by Jayne and St. Laurent is widely used for parameterizing turbulent mixing induced by breaking of internal tides. Based on the internal-tide generation derived from a 0.1° ocean general circulation model, we show that depending on which stratification is used, this relation produces different vertical distributions of internal-tide generation. When using the buoyancy frequency at the seafloor, which is a common practice, the scaling relation produces, relative to the model, too strong internal-tide generation in the upper 2000 m and too weak internal-tide generation in the lower 2000 m. Moreover, the different vertical distributions in the different ocean basins, characterized by a generally decreasing internal tide generation with increasing depth in the Indo-Pacific but not-decreasing or even increasing internal tide generation with increasing depth in the upper 3000 m of the Atlantic, cannot be captured when using bottom stratification. These unsatisfactory features can be easily removed by replacing the buoyancy frequency at the seafloor by a buoyancy frequency averaged over a large part of the water column. To our knowledge, this sensitivity to stratification has not been explicitly quantified for the global ocean. Because of this sensitivity, the scaling relation of Jayne and St. Laurent should be used with an averaged stratification to ensure a more adequate representation of turbulent diffusivity due to tidal mixing and water mass transformation in the deep oceans.

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Section: A Comparison Of E Lvs With Other Estimates Of Internal Tide ...mentioning

confidence: 88%

Sensitivity of Internal-Tide Generation to Stratification and Its Implication for Deep Overturning Circulations

Lüschow,

von Storch

2024

Journal of Physical Oceanography

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“…The hypsometry of our canyon is insufficient to produce the observed upwelling (see Methods). Global estimates of diapycnal velocities based on a parametrisation of tidal mixing yield boundary-focused upwelling velocities up to ∼ 1 × 10 −3 m day −1 in the abyssal ocean 50 . Differences between the 0.5 • resolution bathymetry used and local topography may lead to lower turbulence values than are required to give the upwelling observed here.…”

Section: Discussionmentioning

confidence: 99%

Observational evidence of diapycnal upwelling within a sloping submarine canyon

Wynne-Cattanach,

Alford,

Couto

et al. 2023

Preprint

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Small-scale turbulent mixing drives the upwelling of deep water masses in the abyssal ocean as part of the global overturning circulation (Wunsch & Ferrari 2004). However, the processes leading to mixing and the pathways through which this upwelling occurs remain insufficiently understood. Recent observational and theoretical work suggests that deep water upwelling may be focused in bottom boundary layers on the ocean’s sloping seafloor; however, direct evidence of this is lacking (Ledwell et al. 2000, St. Laurent et al. 2001, Ferrari et al. 2016, de Lavergne et al. 2016). Here, we present observations from a near-bottom dye release within a canyon on the North Atlantic continental slope showing upwelling across density surfaces at a rate of 250 +/- 75 m/day over three days, ∼10,000 times higher than the global average value required to account for ∼30 Sv of upwelling globally (Munk 1966). The vigourous upwelling is coupled with adiabatic exchange of near-boundary and interior fluid. These results provide direct evidence of strong, bottom-focused diapycnal upwelling in the deep ocean, supporting previous suggestions that mixing at topographic features, such as canyons, leads to upwelling.

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“…Small-scale turbulent diapycnal mixing caused by breaking internal waves contributes to maintaining the large-scale overturning circulation (Talley 2013;Cimoli et al 2023). This process can be understood as: (i) a forcing problem, detailing the large-scale sources of internal wave field, and (ii) a dynamical problem, describing the energy cascades from internal waves toward small scales until it turns, by shear or convective instabilities (Staquet and Sommeria 2002), into turbulent kinetic energy.…”

Section: Interior Mixing By Wave-eddy and Wave-wave Interactionsmentioning

confidence: 99%