Influence of Meridional Overturning Circulation on Ocean Heat Storage Rate in an Idealised Climate Model

We present results from an abrupt CO₂-doubling perturbation experiment using a coupled atmosphere-ocean-ice model with simple geometry. The model uses the idealised ‘Double-Drake’ (DDrake) configuration seen in previous work (Ferreira et al. 2010), whereby meridional barriers extending from the sea floor to the sea surface separate the ocean into a small basin and a large basin. We find that the small basin warms at a faster rate than the large basin by 0.6 ± 0.1 W m⁻² over the course of the simulation. The small basin exhibits a deep overturning circulation akin to the Atlantic’s meridional overturning circulation (AMOC), while the large basin does not. We argue that the small basin MOC enables the rapid uptake of surface temperature anomalies into the ocean interior, and is responsible for the contrast in ocean heat storage rates between the small and large basins. Although the presence of a MOC is important for this heat storage contrast, the MOC strength is surprisingly unimportant. The heat storage contrast remains almost constant despite the fact that the MOC strength weakens significantly by ~25%. These results further support the idea that the AMOC plays an important role in ocean heat storage under global warming, but cast doubt on the possibility that surface temperatures may soar if we see a pronounced weakening of this circulation in the future.