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West Antarctica: affects its own climate (Steig summary: (Significance -…
West Antarctica: affects its own climate
WAIS Question
Showed much thinner WAIS during last interglacial Eemian ~ 125 kyr
If this did happen in Eemian...
Could WAIS thin a lot soon? (interglacial @ present)
Poses
questions:
What's the atmos fingerprint of such a change?
How would atmos circulation & temp differ wrt its present state ?
Is it detectable ?
Is there a way to prove whether WAIS was thinner ?
Ice Model (Pollard & DeConto 2009)
Dipole Temp Pattern
Due to cyclonic circulation
Warmer maritime air blown onto N. WAIS
Colder air to south
Eemian
If WAIS were thinner - atmos column stretched
∴ cyclonic circulation introduced (clockwise)
to conserve vorticity
∴ More cold air blown onto WAIS
Steig
Methods
Variety of atmospheric models
run over Modern Antarctica & predicted thinner Antarctica
Examine changes to atmospheric circulation & temp
Steig Model Findings
Dipole pattern in temperature
Heating to the North e.g. Weddell Sea
Cooling around Amundsen & Ross Seas
n.b. not all models agreed
Cause: Velocity pattern differs to today
--> Cyclonic circulation
Potential temperature
removes ambiguity of actual temp
since altitude would've differed with thinner WAIS & different sealevel
Potential
temp:
Temp an air parcel would have if:
Lowered to sea level
Not allowed to exchange heat w/surroundings
i.e. retains heat from compression etc
nearly always > actual temp
Diple Temp Cause
Dipole temp pattern due to cyclonic circulation (clockwise)
Cause:
Thinner Ice - stretches atmospheric column
∴ Vorticity = more negative (more anticlockwise)
Testing Eemian dipole temps theory
If WAIS was lower in Eemian, would expect WAIS temps < EAIS
Mt Moulton Core - SW edge WAIS
Significantly colder temps than EAIS cores i.e. lower δ18O
∴ Eemian WAIS likely was thinner
Not irrevocable proof - need more cores
Did it collapse ?
Steig
summary:
Lowering of WAIS causes large scale wind disturbance
∴ Dipole temp pattern existed over Antarctica (heating/cooling)
But mainly WAIS
Oxygen isotope evidence from last interglacial
= consistent with this dipole temp pattern
WAIS was lower / thinner in Eemian
This altered atmos circulation
Significance - study suggests:
Ice sheets can influence their own growth & climate
WAIS could thin signif / collapse in future