Choose a western boundary current in the ECCO dataset available as preprocessed netcdf in fox-kemper.com/data (I've regridded to eliminate staggered grids and time-averaged for you). Study its volume transport (via u and v) and return flow (via the Sverdrup relation). Time mean fields are fine, but you might want to check out the full set.
Quantitative aspects: Does the budget across a latitude line close? Is the flow at the surface or deep or throughout? Is there a northward heat flux implied by this flow?
That is, consider \int v dz. There are 3 ways to get at it: