1. Antarctic Climate Response to Ozone Depletion in a Fine Resolution Ocean Climate Mode by Cecilia Bitz 1 and Lorenzo Polvani 2 1 Atmospheric Sciences, University of Washington 2 Applied Physics and Applied Mathematics and Earth and Environmental Sciences, Columbia University with thanks to Jean-François Lamarque, Peter Gent, Frank Bryan, and the Peta-Apps team

2. How have increased westerlies influenced sea ice? Million Square Kilometers Antarctic Arctic

3. Turner et al 2009

4. 0 10 20 30 40 50 60 Current Speed in cm/s for randomly chosen October Simulated Surface Currents and Sea Ice Extent Around Antarctica 0.1 degree Simulation 1 degree Simulation

5. Weddell Sea

6. Ozone Depletion Stratospheric Cooling Polar Vortex Spins up Surface Westerlies Strengthen Around Antarctica How does Earth’s Climate Respond to Ozone Depletion? Stratospheric Cooling

7. Simulations using Community Climate System Model Version 3.5 with Ozone Anomaly from SPARC datasets for CMIP5 At two ozone levels: High Ozone (1940s) or “Normal” Low Ozone (1997) or “Most depleted” At two resolutions: Coarse - 1 degree ocean and sea ice Fine – 0.10 degree ocean and sea ice Four runs in total, each 50 yr long – ramp ozone 20 yr and hold fixed for 30 yr. Results shown are differences of last 30 yr.

8. Low Resolution Sensitivity of Temperature and Winds is about 15-20% greater DJF Atmospheric Zonal-Mean Response to Depleting Ozone latitude 7.5 °C °Cm/s Temperature change wind change (color) mean wind (contour lines)

9. Annual Mean Surface Air Temperature Response to Ozone Loss 0.1° Simulations1° Simulations

10. Annual Mean Sea Ice Concentration Response to Ozone Loss 0.1° Simulations1° Simulations

11. dimes.ucsd.edu heat out heat in Surface westerly winds blow on the Southern Ocean Heat exits ocean near Antarctica and enters on northern edge of ACC

12. Ocean Temperature Response to Ozone Depletion for Mar. to Nov. (about the same annually) Color contour interval is 0.1 deg Celsius Fine resolution ocean has a weaker response 0.1° Simulations1° Simulations

13. Normal Sea Ice Mass Balance Sea ice AA Ice transport net growthnet melting

14. Sea Ice Mass Balance Response to ozone loss Sea ice AA Ice transport flux is REDUCED growth decreases here melting increases here Less growth/more melt in pack ice is the reason the ice concentration declines with ozone loss

15. Horizontal Heat Transport by the Ocean in PetaWatts (10 15 W) In Fine Resolution Simulation Total Mean Eddies Latitude (plus gyres)

16. 1° Simulations Latitude 0.1° Simulations Latitude Northward Ocean Heat Transport Response to Ozone Loss Total Mean Eddies The low resolution model has a larger, albeit modest, increase in poleward eddy heat flux, while the high resolution model has almost no change

17. Conclusions The quasi-equilibrium response to ozone depletion is reduced Antarctic sea ice concentration and warmer surface air temperature (in agreement with Sigmond and Fyfe, 2010; Smith et al, 2012) The sea ice response is dominated by thermodynamic changes, despite changes to ice motion Below the surface, the low resolution ocean response is stronger. But on average the SST and sea ice response is about the same. In the 21 st century, ozone will recover and we can expect it to partially offset global warming effects on Antarctic sea ice loss, surface warming, and large-scale oceanic heat transport towards the shelves.

18. Annual Mean Ocean Surface Heat Flux Response to Ozone Loss 0.1° Simulations 1° Simulations 10 6 2 -2 -6 -10 W m -2

19. 0.1° Simulations Latitude 1° Simulations Latitude Northward Ocean & Atmospheric Heat Transport Response to Ozone Loss Ocean The atmospheric heat transport change is as large as the ocean’s south of 65S, compensation is poor Atmosphere Ocean Atmosphere

20. Normal Sea Ice Mass Balance Sea ice AA Ice transport net growthnet melting thermodynamics dynamics ice concentration tendency % day -1

21. Sea Surface Height Change from Ozone Loss (change is from solid to dashed colored contours, 50 cm contour interval) with sea ice extent (heavy black), annual means 0.1° Simulations 1° Simulations Moderate ACC shift in Atlantic and Indian sectors. ACC increases by about 2 Sv (from ~170 Sv) at both resolutions

22. Annual Mean SST Response to depleting ozone 40S 50S 60S 70S 40S 50S 60S 70S 0.5 0 -0.5 0 20 50 time (years) O 3 ramped O 3 fixed °C 0.1° Simulations1° Simulations

25. Schematic of the Overturning Circulation from Marshall and Speer (2012) westerly heat in heat out Ozone depletion speeds up westerlies, Ekman response is to move ocean waters northward, causing surface cooling near Antarctica. But sucking up causes upwelling, which …

26. 0.1° Simulations Latitude ~1Sv 1° Simulations Latitude ~2Sv Sv Contour Interval is 0.5 Sv Annual Mean Global MOC response includes parameterized eddy-effect

27. Annual Mean, Zonal Mean Sea Ice Concentration Response to Ozone Loss 0.1° Simulations 1° Simulations Concentration change %

28. DJF Lowest Level Zonal Wind Speed Response to depleting ozone 0.1° Simulations 1° Simulations Low level zonal wind response is significantly larger in low resolution model m/s

29. Annual Zonal Mean Ocean Temperature Response to Ozone Loss Depth - m Antarctica 1° Simulations Latitude °C Antarctica 0.1° Simulations

30. Annual Zonal Mean Ocean Temperature Response to Ozone Loss Upward Heat Transport Change across 45 m depth Strengthened meridional overturning circulation brings CDW up 1° Simulations 0.1° Simulations W m -2 Depth - m Antarctica 1° Simulations Latitude °C Antarctica 0.1° Simulations