The effect of GIA models on mass-balance estimates in

Antarctica

Riccardo Riva, Brian Gunter, Bert Vermeersen, Roderik Lindenbergh and Hugo Schotman

Department of Earth Observation and Space Systems (DEOS)Delft University of Technology

GRACE Science Team Meeting, Potsdam, 17 October 2007

Introduction

• Glacial Isostatic Adjustment (GIA):• Ice model (ice distribution at LGM, melting history)• Earth model (lithospheric thickness, mantle viscosity, lateral

variations)

• Secular geoid changes:• Surface mass variations• Internal mass redistribution (GIA, seismo-tectonic processes,

…)

• Antarctic mass variability:• Snow accumulation up to 2000 Gt/yr• Predicted unbalance up to 200 Gt/yr

Ice models: IJ05 and ICE-5G

IJ05 by Ivins and James (2006):

• for Antarctica

• mainly from geological data

• free from a specific Earth model

• local constraints on total ice melt

• earlier and gradual deglaciation

• ice melting in East Antarctica

mainly along the coast

ICE-5G by Peltier (2004):

• for the whole Earth

• mainly from sea-level data

• tied to Earth model VM2

• global constraints on total ice

melt

• later and sudden deglaciation

• ice melting also on internal

East Antarctica

Antarctic eustatic sea-level rise from LGM

Ice load at 21 kyr before present (LGM)

IJ05 ICE-5G

Ice load at 11 kyr before present

IJ05 ICE-5G

Ice load at 7 kyr before present

IJ05 ICE-5G

Present-day GIA

IJ05 ICE-5G

RL04 GSM mass variability (2006-2003)

GIA-corrected GRACE

GRACE - IJ05 GRACE - ICE-5G

GIA variability I: IJ05

Min: 40 Gt/yr(litho 120, UM 1021, LM 1023)

Max: 90 Gt/yr(litho 65, UM 1021, LM 4x1021)

GIA variability II: ICE-5G

Min: 25 Gt/yr(litho 120, UM 1020, LM 1021)

Max: 150 Gt/yr(litho 65, UM 1021, LM 1022)

GIA variability III: upper vs. lower mantle viscosityand lithospheric thickness

GIA: northern hemisphere contribution

Ice model: ICE-5GEarth model: VM2

Mass change: 17 Gt/yr

Antarctic mass change estimates

• IJ05: 82 ± 25 Gt/yr• ICE-5G: 105 ± 64 Gt/yr

• GRACE: 44 ± 20 Gt/yr

• GRACE - IJ05: -38 ± 32 Gt/yr (0.10 mm/yr e.s.l.)• GRACE - ICE-5G: -61 ± 67 Gt/yr (0.15 mm/yr

e.s.l.)

Conclusions

• Antarctic ice mass loss derived from GRACE is in the range 0-120 Gt/yr, (0-3 mm/yr e.s.l.) depending on the GIA model (40-170 Gt/yr).

• Due to different ice distribution and deglaciation history, IJ05 andICE-5G have very different GIA signatures, especially regarding their response to mantle viscosity.

• Peak GIA values are mostly smaller than GRACE values, but GIA total mass change can still be larger due to its positiveness.

• GIA due to ice loads in the northern hemisphere, though locally small, represents and important contribution to the total mass change.

0 5 10 15 20 25 30 35 40

-400

-300

-200

-100

0

100

200

300

400

500

1 confidence band

Gig

ato

ns

(GT

)

Months since October 2003

Total Mass Difference (TMD) TMD - IJ05 TMD - ICE5G

-76.2 GT/yr

-54.8 GT/yr

44.3 GT/yr

RL04 GSM Mass Variability

GIA: West vs. East Antarctica

Leakage I

Leakage II