Two companion papers on deep ocean mixing, eddies, and tracer transport published in Journal of Physical Oceanography

Part 1: Dynamics of eddying abyssal mixing layers over sloping rough topography

This paper uses a hierarchy of idealized models, from approximate analytical solutions in terms of elementary functions to non-linear simulations requiring high performance computers, to understand how small-scale turbulence mixing can drive strong flows along gently sloping ocean topography such as Mid-Atlantic Ridges.

By adding in the complexity of the real ocean one step at a time, we can understand how several individual processes combine to produce the complicated patterns we observe in reality.

(b),(c) Height above bottom-averaged stratification profiles at t = 5000 days, as a function of model complexity (lines) and domain subregion. (a) 1D solutions with the same parameters as the BBTRE simulations (solid); without a mean-slope (dashed), without rotation (f = 0; dotted); and with an enhanced along-slope turbulent Prandtl number (dash-dotted), a crude proxy for restratification by submesoscale baroclinic eddies (dash–dotted) [also shown in gray lines in (b) and (c)]. Colored lines show a hierarchy of 3D simulations with increasingly complex topographies (see figure above). Arrows show how the stratification profiles evolve when processes are added: 1) adding a mean slope, 2) allowing 3D eddies, 3) introducing a cross-slope canyon, 4) blocking the canyon with a sill, and 5) adding realistic hills (i.e., the BBTRE topography).

Part 2: Diapycnal displacement, diffusion, and dispersion of tracers in the ocean

This paper presents a new theoretical framework for exactly comparing in-situ estimates of ocean mixing rates with bulk rates inferred from the spreading of an injected tracer, which improves upon previous approximate methods that assume a direct relationship between diffusion and dispersion.

We use high-resolution quasi-realistic simulations to generate synthetic observations that demonstrate, at least as a proof-of-concept, that the new method provides less ambiguous estimates of ocean mixing.