Global Mixing Paper Submitted

I have finally managed to submit this paper to JGR-Oceans. The paper represents our attempt to use passive-tracer-based methods to diagnose mixing rates globally. The basic method was developed by John, Emily Shuckburgh, Helen Jones, and Chris Hill in a 2006 paper. Here we attempt to apply this method globally to produce a map of mixing rates everywhere.

Abernathey, R. and J. Marshall, Mixing of Passive Tracers by the Surface Geostrophic Flow, J. Geophys. Res., submitted, 2012.

The results can be summed up by this figure, a global map of passive-tracer mixing rates.


Velocities derived from AVISO sea-surface height observations are used to simulate the evolution of passive tracers at the ocean surface. The simulations are used to diagnose eddy mixing rates in two ways. First, the method of Nakamura is applied to a sector in the East Pacific. Second, the Osborn-Cox diffusivity is calculated globally in two dimensions. Experiments are carried out with and without the mean flow present. The results from the East Pacific show weak meridional mixing at the surface in the Southern Ocean (< 1000 m^2 s^{-1}), consistent with previous results), but higher mixing rates (~ 3000-5000 m^2 s^{-1}) in the tropical ocean. The Osborn-Cox diagnostic provides a truly global picture of mixing rates and agrees qualitatively with the results from the East Pacific. It also shows extremely high mixing rates (~ 10^4 m^2 s^{-1}) in western-boundary-current regions. The Osborn-Cox diffusivity is sensitive to the tracer initialization, which we attribute to the presence of anisotropic mixing processes. The mixing rates are strongly influenced by the presence of a mean flow nearly everywhere, as shown by comparison an eddy-only calculation.  Finally, results are compared with other recent estimates of mixing rates using Lagrangian and inverse methods.

Here is a movie I made of one of the tracer advection experiments. Experiments such as this were used to diagnose the mixing rates.

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