Antarctic Climate Response to Ozone Depletion in a Fine

Resolution Ocean Climate Mode

by Cecilia Bitz1 and Lorenzo Polvani2

1Atmospheric Sciences, University of Washington2Applied 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

How have increased westerlies influenced sea ice?

Mill

ion

Squ

are

Kilo

met

ers

Antarctic

Arctic

Turner et al 2009

0 10 20 30 40 50 60

Current Speed in cm/s for randomly chosen October

Simulated Surface Currents and Sea Ice Extent Around Antarctica0.1 degree Simulation1 degree Simulation

Weddell Sea

How does Earth’s Climate Respond to Ozone Depletion?

Stratospheric Cooling

Simulations using Community Climate System ModelVersion 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 iceFine – 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.

Low Resolution Sensitivity of Temperature and Winds is about 15-20% greater

DJF Atmospheric Zonal-MeanResponse to Depleting Ozone

latitude latitude

7.5 °C

°C m/s

Temperature changewind change (color)

mean wind (contour lines)

Annual Mean Surface Air Temperature Response to Ozone Loss

0.1° Simulations 1° Simulations

Annual Mean Sea Ice Concentration Response to Ozone Loss

0.1° Simulations 1° Simulations

dimes.ucsd.edu

heat out

heat

in

Surface westerly winds blow on the Southern OceanHeat exits ocean near Antarctica and enters on northern edge of ACC

Ocean Temperature Response to Ozone Depletionfor Mar. to Nov. (about the same annually)

Color contour interval is 0.1 deg Celsius

Fine resolution ocean has a weaker response

0.1° Simulations 1° Simulations

Normal Sea Ice Mass Balance

Sea iceAA

Ice transport

net growth net melting

Sea Ice Mass Balance Response to ozone loss

Sea iceAA

Ice transport flux is REDUCED

growthdecreases here

melting increases here

Less growth/more melt in pack ice is the reason the ice concentration declines with ozone loss

Horizontal Heat Transport by the Ocean in PetaWatts (1015 W)

In Fine Resolution Simulation

Total

Mean

Eddies

Latitude(plus gyres)

1° Simulations

Latitude

0.1° Simulations

Latitude

Northward Ocean Heat TransportResponse 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

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 21st 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.

Annual Mean Ocean Surface Heat Flux Response to Ozone Loss

0.1° Simulations1° Simulations10

6

2

-2

-6

-10

W m-2

0.1° Simulations

Latitude

1° Simulations

Latitude

Northward Ocean & Atmospheric Heat TransportResponse 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

Normal Sea Ice Mass Balance

Sea iceAA

Ice transport

net growth net melting

thermodynamics

dynamics

ice concentration tendency % day-1

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° Simulations1° Simulations

Moderate ACC shift in Atlantic and Indian sectors. ACC increases by about 2 Sv (from ~170 Sv) at both resolutions

Annual Mean SST Response to depleting ozone

40S

50S

60S

70S

40S

50S

60S

70S

0.5

0

-0.5

0 20 50 0 20 50

time (years) time (years)

O3 ramped O3 fixed O3 ramped O3 fixed

°C0.1° Simulations 1° Simulations

Schematic of the Overturning Circulation from Marshall and Speer (2012)

wes

terly

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 …

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

Annual Mean, Zonal Mean Sea Ice Concentration Response to Ozone Loss

0.1° Simulations

1° Simulations

Con

cent

ratio

n ch

ange

%

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

Annual Zonal Mean Ocean Temperature Response to Ozone Loss

Dep

th -

m

Ant

arct

ica

1° Simulations

Latitude°C

Ant

arct

ica

0.1° Simulations

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° Simulations0.1° Simulations

W m

-2

Dep

th -

m

Ant

arct

ica

1° Simulations

Latitude°C

Ant

arct

ica

0.1° Simulations