Understanding the Delayed Warming of the Southern Ocean

Here, a fully coupled model run at multiple resolutions from coarse to eddy resolving, driven by observed historical and fixed CO₂ concentration is used to investigate the delayed warming of the Southern Ocean (SO). We analyze the 1941-2014 Southern Ocean sea surface temperature (SST) and ocean potential temperature for the first 1 km trends simulated in couple general circulation model and evaluate possible causes of the models’ inability to reproduce the observed 1941-2014 SO cooling. We used NCAR’s Community Climate System Model version 4 (CCSM4) at both eddy resolving (0.1 degree ocean model) and eddy parameterized resolutions (1 degree ocean model) to explore the mesoscale atmosphere-ocean interactions in the Southern Ocean in a fully coupled regime and to understand the role of ocean dynamics in modulating temperature response. At both resolutions the models successfully reproduce the observed warming response for the northern flank of the Antarctic Circumpolar Current (ACC). The eddy resolving simulations are able to reproduce the observed SO cooling, however in the eddy parameterized simulations, the SO SST response is inconsistent with the observations for the south of the Antarctic Circumpolar Current. The results presented here provide support for the hypothesis that the cooling around the Antarctic is intimately connected with ocean meso-scale processes that cannot be captured by ocean eddy parameterized models typically used for IPCC simulations.