Subduction by Submesoscales

Abstract

AbstractSeveral studies have demonstrated the relevance of submesoscales (SM) to the production of phytoplankton and the ocean absorption of anthropogenic CO2. One variable that thus far has not been fully quantified is the SM‐induced rates of subduction and obduction at the bottom of the mixed layer. In this work, we use an SM parameterization that had been previously assessed to estimate the rates of subduction‐obduction using a coarse resolution stand‐alone ocean code to compute the large‐scale fields. To separate the contributions of baroclinic instabilities from those due to wind stress, we derive an analytic expression for the SM subduction‐obduction rates. Since there are no numerical simulations and/or measurements to assess the results, we compare them to subduction rates due to mesoscales for which an eddy‐permitting southern ocean state estimate is available. An interesting result is that in the Antarctic Circumpolar Current the maximum SM subduction rates are not significantly smaller than those due to mesoscales, but the SM subduction rates exhibit a topology opposite to that of mesoscales: obduction is equatorward and subduction is poleward. Sensitivity studies are presented to explore the dependence of the results on the depth of the SM vertical extent and the SM kinetic energy. On the basis of these results, it is suggested that the SM‐induced subduction should not be neglected because topology and magnitude indicate that mesoscales and submesoscales may add to or subtract from one another.