Water Mass Transformation by Near-Surface Mesoscale Eddy Stirring

Abstract:

The water-mass-transformation framework consolidates all the thermodynamic processes which irreversibly modify density and can be used to infer subduction and upwelling in a basin. Diapycnal mixing is an important such transformation process. Mesoscale eddies can contribute to diapycnal mixing near the surface by stirring across the surface density gradient, although this term is frequently neglected from the water mass budget. Here we present a global diagnosis of this mesoscale-diapycnal transformation rate from a coupled climate model with a one-tenth degree ocean. The analysis focuses on the mode and intermediate water production regions in the Atlantic, Pacific, and Southern oceans. Near-surface mesoscale-diapycnal transformation is shown to be most active in the presence of high eddy energy and deep mixed layers.