1) The study finds substantial interannual variability in ice shelf height in the Amundsen Sea region that is linked to the El Niño-Southern Oscillation (ENSO) cycle, with ice shelves thickening during El Niño events and thinning during La Niña events on average. 2) While ocean melting may increase ice shelf thinning during El Niño, increased precipitation outweighs this effect and leads to overall thickening. 3) The Getz Ice Shelf shows the strongest response to ENSO variability in ice shelf height changes across West Antarctica.

1. Ice-shelf height variability in
Amundsen Sea linked to ENSO
Fernando S. Paolo
We thank Susan Howard (ESR)
This work is funded by NASA
European Geosciences Union 2016
Scripps Oceanography
?
Helen A. Fricker
Scripps Oceanography
Laurie Padman
Earth & Space Research
NOAA

2. 18 years of continuous observations
over the Antarctic ice shelves
Time: ~3 months
Space: ~30 km
Span: 1994–2012
Paolo et al. (2015)
Paolo et al. (2016), RSE

3. There is substantial variability in AS
ice-shelf height at interannual time scales
Total of 140 time series in AS

4. Multivariate Singular Spectrum Analysis
identifies common oscillatory modes
Vautard et al. 1992, Golyandina et al. 2001, Ghil et al. 2002,
Time
Multivariatedataset
Time
Reconstructedcomponent
Window
Rank
EigenvectorEigenvalue
Signal
Noise

5. There is statistically significant energy in AS
ice-shelf height at the interannual band
Ice-shelf height time series
T = 4.2 yr
Oceanic Niño Index (SST)
NOAA
T = 4.2 yr

6. Ice-shelf height variability
Low-freq. mode of ENSO
El Niño events
Interannual change in AS ice-shelf height
is strongly correlated with ENSO
Reconstructing AS and ONI using EOFs 1+2:

7. Sea-ice and precipitation variability in AS are
also correlated with ice-shelf change
Observed
sea-ice
concentration
interannual
anomaly
(NSIDC-SSMI)
Modeled
precipitation
rate
interannual
anomaly
(ERA-Interim)

8. There is a clear
relationship between
sea ice cover,
precipitation rate,
ice-shelf change,
and ENSO
(at interannual scale)
EN EN EN

9. There is significant contrast in local conditions
between El Niño and La Niña (of 1997-2000)
El Niño 1997-98 La Niña 1999-00
Wind and
vertical transport
(ERA-Interim)
Surface
temperature
(ERA-Interim)

10. Precipitation
rate
(ERA-Interim)
Sea ice
concentration
(NSIDC-SSMIS)
El Niño 1997-98 La Niña 1999-00
There is significant contrast in local conditions
between El Niño and La Niña (of 1997-2000)

11. Interannual sea-ice and ice-shelf variability
in Amundsen are linked in opposite phase
Increase in coastal polynyas allowing
enhance ocean-to-atmosphere
exchange of heat
Increase in snowfall
along the coast
Overall reduction
of sea-ice cover in AS
During El Niño (1997–98):
Increase surface moisture
and poleward moisture transport
The opposite conditions are
observed during La Niña (1999–01) Ice shelves thicken!

12. The ENSO signal is stronger in the
Amundsen Sea ice shelves
Strength of ENSO along
the West Antarctic margin
(on each individual ice shelf)

13. Summary 1
ENSO is an important source of
interannual variability in the WAIS margin
Ice shelves thicken during El Niño
and thin during La Niña (on average)
Not only magnitude, but also duration
of El Niño and La Niña matters

14. Summary 2
Though oceanic melting may increase
during El Niño, precipitation wins (in dh!)
Getz is epicenter of ENSO ice-shelf
response in West Antarctica
Pine Island Bay variability is
anomalous w.r.t. the broader AS

15. Thank you.

16. Longer-term implication
These results suggest that changing
precipitation and air temperature patterns
could be more important to long-term ice-
shelf stability than changes in basal melting
caused by ocean circulation variability

17. Mass budget between El Niño and La Niña:
How much due to atmosphere and ocean?
dh_obs = h(La Niña) - h(El Niño)
dh_obs = dh_ibe + dh_smb + dh_bmb dh_smb > dh_bmb
rho_i = 350—500

18. time 1 time 2
H1
H2
= ( / ) ⇥