The role of sidewalls in determining the interior distribution of potential vorticity (PV) is investigated using eddy-resolving isopycnic experiments. The layer model is integrated at 1 ⁄ 16 Њ resolution for a wind-driven double gyre with either vertical or sloping sidewalls. If there are vertical sidewalls, eddy stirring leads to PV homogenization within unforced, interior density layers. If there are sloping sidewalls, frictional torques lead to bands of low and high PV being formed along the

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... western boundary of the subpolar and subtropical gyres, respectively. These regions of low and high PV are transferred into the interior by a separated jet at the intergyre boundary. Over a limited domain, this injection of the PV contrast can prevent eddy homogenization from occurring. However, over a larger-scale domain, eddies provide a downgradient transfer of PV, reducing the PV contrast downstream along the jet and enabling homogenization to occur for intermediate layers within the basin interior. Diabatic mixing along the slope can introduce low PV for intermediate layers and even mask the frictional contributions.