Ice-shelf height variability in Amundsen Sea linked to ENSO
Fernando S. Paolo
We thank Susan Howard (ESR)This work is funded by NASAEuropean Geosciences Union 2016
Scripps Oceanography
?
Helen A. FrickerScripps Oceanography
Laurie PadmanEarth & Space Research
NOAA
18 years of continuous observationsover the Antarctic ice shelves
Time: ~3 monthsSpace: ~30 kmSpan: 1994–2012
Paolo et al. (2015)Paolo et al. (2016), RSE
There is substantial variability in ASice-shelf height at interannual time scales
Total of 140 time series in AS
Multivariate Singular Spectrum Analysisidentifies common oscillatory modes
Vautard et al. 1992, Golyandina et al. 2001, Ghil et al. 2002,
Time
Mul
tivar
iate
dat
aset
Time
Rec
onst
ruct
ed c
ompo
nent
Window
Rank
Eige
nvec
tor
Eige
nval
ue
Signal
Noise
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
Ice-shelf height variability
Low-freq. mode of ENSO
El Niño events
Interannual change in AS ice-shelf heightis strongly correlated with ENSO
Reconstructing AS and ONI using EOFs 1+2:
Sea-ice and precipitation variability in AS arealso correlated with ice-shelf change
Observedsea-ice
concentrationinterannual
anomaly(NSIDC-SSMI)
Modeledprecipitationrateinterannualanomaly(ERA-Interim)
There is a clearrelationship betweensea ice cover,precipitation rate,ice-shelf change,and ENSO(at interannual scale)
EN EN EN
There is significant contrast in local conditionsbetween 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)
Precipitationrate
(ERA-Interim)
Sea iceconcentration
(NSIDC-SSMIS)
El Niño 1997-98 La Niña 1999-00
There is significant contrast in local conditionsbetween El Niño and La Niña (of 1997-2000)
Interannual sea-ice and ice-shelf variabilityin 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 reductionof 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!
The ENSO signal is stronger in the Amundsen Sea ice shelves
Strength of ENSO alongthe West Antarctic margin(on each individual ice shelf)
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 durationof El Niño and La Niña matters
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 isanomalous w.r.t. the broader AS
Thank you.
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
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
time 1 time 2
H1H2
�� = (�� ����/����)�� ⇥ �����
����������
��