Impacts of Stratospheric Ozone Recovery on Southern Ocean Surface Temperature

The projected stratospheric ozone recovery could significantly affect the Southern Ocean’s surface temperature through its impacts on surface radiation, Ekman advection, and entrainment. In order to better understand the roles of these processes in determining the Southern Ocean surface temperature responses to ozone recovery, we conduct two sets of ensemble simulations of 2010-2100 using the coupled ocean Goddard Earth Observing System Chemistry-Climate Model. The first ensemble is forced with changing concentrations of greenhouse gases and ozone depletion substances (ODSs). The second ensemble is the same as the first one except that the ODSs are fixed at 2010 levels. The impacts of stratospheric ozone recovery on the Southern Ocean surface temperature are investigated by the differences in the mixed layer heat budget between these two ensembles.

We focus on the Antarctic seasonal sea ice zone (58˚S-68˚S) where changes in sea surface temperature have strong implications for sea ice changes. The model results show that in this area ozone recovery leads to significant warming in December-February and cooling in May-November. Diagnoses of the mixed layer heat budget reveal that the summer warming is mainly due to an increase in surface heat flux, with small contributions from reduced equatorward Ekman advection of cold seawater. Significant cooling in winter and spring is mostly caused by entrainment of colder deep seawater into the mixed layer during January-March. It is found that these oceanic process responses are strongly related to the weakening and equatorward shift of the tropospheric jet.