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The abyssal southwest Pacific basin has warmed significantly between 1992 and 2017, consistent with warming along the bottom limb of the meridional overturning circulation seen throughout the global oceans. Here we present a framework for assessing the abyssal heat budget that includes the time-dependent unsteady effects of decadal warming and direct and indirect estimates of diapycnal mixing from microscale temperature measurements and finescale parameterizations. The unsteady terms estimated from the decadal warming rate are shown to be within a factor of 3 of the steady-state terms in the abyssal heat budget for the coldest portion of the water column and therefore cannot be ignored. We show that a reduction in the lateral heat flux for the coldest temperature classes compensated by an increase in warmer waters advected into the basin has important implications for the heat balance and diffusive heat fluxes in the basin. Vertical diffusive heat fluxes are estimated in different ways: using the newly available CTD-mounted microscale temperature measurements, a finescale strain parameterization, and a vertical kinetic energy parameterization from data along the P06 transect along 32.5°S. The unsteady-state abyssal heat budget for the basin shows closure within error estimates, demonstrating that (i) unsteady terms have become consequential for the heat balance in the isotherms closest to the ocean bottom and (ii) direct and indirect estimates from full-depth GO-SHIP hydrographic transects averaged over similarly large spatial and temporal scales can capture the basin-averaged abyssal mixing needed to close the deep overturning circulation. Significance Statement: The deep overturning circulation of the ocean is driven by northward flow of cold waters formed in the Southern Ocean and diffusion-driven upwelling from oceanic turbulence, both of which are difficult to measure and quantify accurately. This study aims to reconcile different methods of measuring the overturning in a large ocean basin by 1) inferring mixing required to sustain the overturning using long-term observations of inflow and outflow heat fluxes from a time-dependent heat budget and 2) direct/indirect observations of mixing within the basin. While our results show consistency of the basin-averaged mixing estimates from several different methods, this study also highlights the need to make sustained oceanic observations of mixing and circulation to further reduce uncertainty in the estimates. [ABSTRACT FROM AUTHOR]