This study builds upon a recent steady-state multi-basin model model of the global overturning circulation by extending the governing equations to include transient dynamics. This isopycnal box model determines the stratification and diabatic water mass transformations in each basin. The idealization to multiple, two-dimensional basins permits zonal mass transport along isopycnals in a Southern Ocean–like channel, while retaining the dynamical framework of residual-mean theory. Our model exhibits abrupt transitions in the overturning structure related to transitions in the Southern Ocean surface buoyancy forcing; hysteresis also occurs. The dominant mechanism for these transitions is a shift in the location of outcropping Lower Circumpolar Deep Water density classes between regions of negative buoyancy forcing in the south (region of sea ice formation) and a region of positive buoyancy forcing located further north in the Antarctic Circumpolar Current (region of sea ice melt and net precipitation). These outcropping transitions respond to transient changes in the vertical stratification of the northern basins following a perturbation in North Atlantic Deep Water strength. This stratification adjustment occurs over a timescale which closely matches the observed 200-year time lag between DO events and AIM events.