Stochastic variability of oceanic flows above topography

Temporal variability of oceanic currents may originate from the oceanic response to some stochastic forcing, from deterministic, non-linear dynamics, or from a complex interplay between both effects.

Here we describe a stochastic variability mechanism which is genuinely internal to the ocean. The key ingredient is the existence of closed contours of bottom topography surrounded by a stirring region of enhanced eddy activity. This leads to the formation of a robust but highly variable vortex above the topography anomaly. For frequencies higher than a cutt-off frequency set by bottom friction, the dynamics integrate the white noise forcing of oceanic eddies into a red noise signal for the mass transport of the vortex.

The transport of the Zapiola anticyclone ($\sim 100$ $Sv$) in the Argentine basin is argued to be an example of such eddy-driven stochastic variability, on the basis of a $300$ year long simulation of a comprehensive ocean model run under climatological forcing.