The Spindown of Bottom-Trapped Plumes

This note considers the decay of a bottom-trapped freshwater plume after the causative freshwater inflow has ceased. It is shown that shortly after the low-density inflow stops, the barotropic pressure field that it created radiates away and the ocean circulation becomes controlled by baroclinic pressure gradients generated by the remnants of the inflow. This produces a reversal of the circulation in the region downstream of the inflow, after which the entire plume starts to move in the upstream direction. The decay of the plume is henceforth controlled by upstream oceanic flow and dilution through cross-isopycnal mixing.