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

Abstract

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.

Glacial ocean circulation and stratification explained by reduced atmospheric temperature

“…The eddy diffusivity is capped between K min = 200 m 2 ·s −1 and Kmax = 2,000 m 2 ·s −1 , and the GM parameterization is tapered in the presence of steep isopycnal slopes, following Gerdes et al (44). Diapycnal mixing is represented by a vertical diffusivity, which is strongly enhanced in the abyss, but reduces to a background value of 2×10 −5 m 2 ·s −1 in the thermocline (45,46). The diffusivity profile is shown in Fig.…”

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

“…Because eddy diffusion coefficients in the vertical are 10 −5 -10 −4 m 2 /s (or greater; Ku and Luo, 1994), over hundreds to thousands of meters per year (horizontal coefficients are even greater), the impact of a benthic flux may potentially integrate over significant depths within the deep ocean. Furthermore, eddy diffusivity is also an order of magnitude higher on the seafloor relative to the water column because of the turbulence created by topography (Waterhouse et al, 2014); therefore, a benthic flux will be dissipated with great efficiency into the water column. This dissipation is the rationale for the observation that there is an apparent jump in REE concentrations between pore water and overlying water (Abbott et al, 2015b(Abbott et al, , 2016.…”

Regional and global climate for the mid-Pliocene using the University of Toronto version of CCSM4 and PlioMIP2 boundary conditions

“…Furthermore, the two different choices of the diapycnal diffusivity will allow us to assess the degree of impact that this parameter has on the strength of the meridional overturning circulation under mid-Pliocene boundary conditions. Given that one of the defining largescale characteristics of the global oceans is the vertical variation in the turbulent diapycnal diffusivity by an order of magnitude, from low values above the thermocline to high values closer to the rough ocean floor (Waterhouse et al, 2014), our POP1 variant simulations will constitute our most accurate PlioMIP2 simulations. It is these simulations that should be used by other groups for intercomparison.…”