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Notes on “The role of eddies in the isopycnic transfer of nutrients and their impact on biological production” by Lee and Williams (2003)

The authors performed idealized simulations of basin-scale eddy turbulence generated from a forced and unstable baroclinic jet. The goal of the study is to “focus on (i) how eddies transfer nutrients into the euphotic zone through advection or diffusion along isopycnal layers, (ii) how the dominant eddy transfer mechanism varies according to the lifetime of the nutrients, and (iii) how the total transport including the wind-driven Ekman and eddy transfer controls the response in realistic regimes”.

Using scaling analysis of the tracer equation, they deduce that a long-lived tracer should be controlled at equilibrium by advection, a short-lived tracer by diffusion. Nitrate, being short-lived, should thus be controlled by diffusion, dissolved nitrate organic, being long-lived, should be controlled by advection.

The model: isopycnal with 5 layers, zonal channel configuration with 10-km horizontal resolution. Buoyancy forcing along the northern and southern boundaries. They do not say anything about the dissipation of momentum in the model. They performed simulations with and without zonal wind, in order to study the effect of having a meridional Ekman flow. Why, in the first case, the time-mean flow is so weak compared to the eddy (Stokes) drift? Should they not both be of second order in eddy amplitude?

The diagnostic applied is that of the zonal and time-averaged flux form of the tracer equation.