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

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