Stochastic variability of oceanic flows above topography anomalies

We describe a stochastic variability mechanism which is genuinely internal to the ocean, i.e., not due to fluctuations in atmospheric forcing. The key ingredient is the existence of closed contours of bottom topography surrounded by a stirring region of enhanced eddy activity. This configuration leads to the formation of a robust but highly variable vortex above the topography anomaly. The vortex dynamics integrates the white noise forcing of oceanic eddies into a red noise signal for the large scale volume transport of the vortex. The strong interannual fluctuations of the transport of the Zapiola anticyclone (∼100 Sv) in the Argentine basin are argued to be partly due to such eddy‐driven stochastic variability, on the basis of a 310 years long simulation of a comprehensive global ocean model run driven by a repeated‐year forcing. Key Points A simple, generic mechanism for intrinsic, low frequency oceanic variability Observation of intrinsic, low frequency variability in the Argentine Basin Explanation of the numerical simulation output with our simple mechanism