A Weakened AMOC Could Cause Southern Ocean Temperature and Sea-Ice Change on Multidecadal Timescales

The Atlantic meridional overturning circulation (AMOC) could substantially weaken over the next century due to climate change. The Southern Ocean (SO) is a key control of global ocean circulation and climate. Here, we use the latest generation of climate models to assess the impacts of this potential AMOC weakening on the SO and Antarctic sea ice, on timescales of less than a century. Following AMOC weakening, ocean transports move heat southwards into the SO, causing SO surface warming and sea-ice loss. We also identify a new atmospheric connection, from the tropics to Antarctica: this connection enhances warming and sea-ice loss in one SO region, but causes cooling and sea-ice growth in another. This shows that substantial AMOC weakening could impact the SO on multidecadal timescales. However, these SO changes resulting from AMOC collapse are much smaller than the projected direct impacts of greenhouse-gas-induced warming.