The effect of a near bottom transport scheme on the sensitivity of the thermohaline circulation is analyzed in a coupled model. In this model with idealized geometry of the Atlantic, it is shown that in the presence of a northern source of deep water, an accurate representation of the overflow process has a stabilizing effect on the thermohaline circulation for subpolar sea surface salinity perturbations. The large scale overturning circulation can be maintained in the presence of a continued deep water formation north of the sill. Experiments suggest that without a sufficient coupling across a sill in the northern North Atlantic, the response of the ocean's circulation to subpolar atmospheric variability may be too strong.