Abstract: The meridional ocean circulation (MOC) plays a key role in modulating the climate through the transport of tracers such as heat and carbon. Diapycnal mixing is integral for the upwelling of abyssal waters, thereby sustaining the deep branch of the MOC. Here we use a low complexity climate model in which tidal power and mixing efficiency both evolve with stratification. We investigate the impact of such changes on the MOC as well as on meridional heat transport and atmospheric pCO2. We do so by running simulations from pre-industrial times to the year 2100 by applying changes to the surface forcings in line with multi-model means from CMIP6 models. We report three primary findings: (I) changes to wave generation and mixing efficiency both have leading order impacts on the MOC, (II) consideration of their covariance is essential; otherwise changes to either in isolation can lead to gross inaccuracy in the MOC prediction, (III) allowing both will add two degrees of freedom to the model and give rise to a strong internal variability signal with frequencies ranging from inter-annual to decadal and centennial. Such variability is entirely absent from any ocean/climate model and may very well contribute to MOC variability as inferred from various proxy records.