Seasonal Stratospheric Cooling Increases Southern Ocean Overturning & Ice Melt

There are concurrent trends in several components of the Earth’s climate system around Antarctica over the last few decades, including: formation of an ozone hole accompanied by significant cooling in the stratosphere over Antarctica every austral spring; a poleward-shift and strengthening of the annual-mean upper-level and surface westerly winds; and increasing sea ice maxima prior to 2014, followed by rapidly-decreasing sea ice extent at the times of both maximum (in September) and minimum (in February) extent since 2016. We use an ensemble of coupled climate model simulations to examine the climatic and dynamical impacts of the observed austral springtime cooling of the Southern Hemisphere stratosphere and to assess potential connections between these observed trends. Here we show that seasonal cooling of the Antarctic stratosphere induces the annual-mean poleward shift and increased speed of the upper-level jet and surface westerlies over the Southern Ocean. The poleward-shifted surface westerlies subsequently induce changes to a variety of measures of ocean mixing and overturning as well as direct changes to the annual-mean sea ice coverage over the Southern Ocean that are consistent with several published papers relating the recent sea ice trends to changes in the surface winds.