Impacts of Stratospheric Ozone Recovery on Southern Ocean Temperature and Heat Budget

The impacts of stratospheric ozone recovery on Southern Ocean surface and interior temperature, heat content, heat uptake, and heat transport are investigated by contrasting two ensemble chemistry-climate model simulations in 2005–2099: one with fixed ozone depleting substances (ODSs) and another with decreasing ODSs. In our simulations ozone recovery significantly affects Southern Ocean temperature, with large latitudinal and vertical variations. Ozone recovery causes a dipole change of the full-depth ocean heat content (OHC) with an increase south of 60°S and a decrease between 45°S and 60°S. Integrated over latitudes south of 40°S, OHC decreases in response to ozone recovery. This ocean heat loss is shown to be driven by weakened poleward ocean heat transport (OHT) across 40°S, which is partly canceled by enhanced heat uptake. The weakening of poleward OHT into the Southern Ocean is caused by the ozone-induced equatorward shift of the meridional overturning circulation. Plain Language Summary With the phaseout of ozone depleting substances as controlled under the Montreal Protocol and its amendments, the stratospheric ozone layer is projected to recover to the pre-ozone hole levels in this century. Stratospheric ozone recovery can influence temperature and circulation in the atmosphere and ocean. Here we study how stratospheric ozone recovery affects Southern Ocean temperature and heat content using a coupled atmosphere-ocean-chemistry model. The strong surface westerlies over the Southern Ocean play a crucial role in ocean circulation and climate. We find that ozone recovery influences Southern Ocean through its impact on the surface westerlies. Our model results show that ozone recovery causes a weakening and equatorward shift of the strong westerlies over the Southern Ocean. As a result, the ocean circulation in the Southern Ocean weakens, leading to a weaker poleward heat transport from the lower latitude into the Southern Ocean. A weaker heat transport results in Southern Ocean cooling and a decrease of the Southern OHC.