The forcing of abyssal recirculation gyres by cross-isopycnal mixing a
nd wave fluxes near the deep western boundary is investigated. A three
-layer isopycnal primitive equation model is applied in a series of ex
periments to an idealized basin with bottom topography. In the absence
of deep western boundary current instabilities, cross-isopycnal mixin
g forces a cyclonic recirculation gyre, modified by topography, which
is consistent with the traditional Stommel-Arons model. Instabilities
of the boundary current fundamentally alter the mean basin-scale deep
flow from a cyclonic recirculation to an anticyclonic recirculation. B
ottom topography plays a key role in destabilizing the mean flow. The
forcing mechanism for the interior recirculation is the horizontal div
ergence of momentum and potential vorticity fluxes carried by topograp
hic waves that are forced by the boundary current instabilities. The s
trength of the recirculation gyre is linearly proportional to the kine
tic energy of the waves, which is controlled in the present model by b
ottom drag, and well predicted by a simple scale analysis. This is ess
entially an adiabatic process. The addition of cross-isopycnal mixing
forces the large-scale interior recirculation toward the pole, partial
ly into boundary currents, through linear vorticity dynamics. Vorticit
y budgets reveal three dynamical regimes for the eddy-driven flows, th
e western boundary current, the recirculation region, and the interior
. Similarities and differences between the mean flow and recent observ
ations in the Brazil Basin are discussed.