Glacial Isostatic Adjustment Contributions to Tide Gauge, Altimetry and GRACE Observations

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Glacial Isostatic Adjustment Contributions to
Tide Gauge, Altimetry and GRACE Observations
Edited version original slides 12-19 removed

• Glenn Milne
• Dept of Earth Sciences
• University of Durham, UK

Contributors Mark Tamisiea, Konstantin Latychev,
Erik Ivins, Philippe Huybrechts, Jerry Mitrovica,
Bert Vermeersen.
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http//www.ngdc.noaa.gov/paleo/slides/slideset/ind
ex11.htm
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GLACIAL ISOSTATIC ADJUSTMENT
Surface Mass Redistribution
Earth
Earth Response

• Relative sea level
• Geopotential
• Rotation vector
• 3D solid surface deformation

Model
Surface load Rotational potential
Rheological Earth model
Constraints on surface mass redistribution
Better understanding of GIA process
Constraints on Earth rheology
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Key Elements of a GIA Model
Earth Forcing
Earth Model
Rotational potential
Surface loading
Geometry
Rheology
Euler equations
Spherical/Flat Internal structure 1D 3D
Viscoelastic Linear and non-linear viscous
deformation
Ice Model
Ocean Model
Multidisciplinary approach
Sea-level equation
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GIA Response Driven by Contemporary and Past
Mass Flux
Tamisiea et al., 2003
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How Can the GIA Community Contribute to a Better
Understanding of Recent Sea-Level Changes?
Ice-ocean mass exchange Ocean warming
Climate change
Anthropogenic effects
Proxy records
Tide Gauges
SEA-LEVEL FORCINGS
SEA-LEVEL OBSERVATIONS
Ocean dynamics
Solid Earth motion
Satellite Altimetry
Ocean-atmosphere interaction
Satellite Gravity
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Viscous Memory of Solid Earth to Past Ice-Ocean
Mass Flux
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A
B
Mitrovica and Milne (2002)
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The Influence of Variations in Earth Model
Viscosity Structure on Observations of Sea-Level
Change

• How sensitive is the GIA signal associated with
  past ice-ocean mass flux to changes in Earth
  model viscosity structure?
• Consider the correction to be applied to tide
  gauges, satellite altimetry and GRACE.
• Is the uncertainty in the correction significant
  compared to errors in the observations?
• Note results based on a single global ice model.

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Employ Careful Selection Criteria to Minimise
Influence of Solid Earth Motion
Douglas, 1997
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SLR1.50.1 mm/yr
SLRGIA1.80.1 mm/yr
I I
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Influence of Radial Mantle Viscosity Variations
on GIA-Correction at Tide Gauge Sites
LT 70-120 km UMV 0.1-1x1021 Pas LMV
2-50x1021 Pas
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GIA Contribution to Observations of Recent
Cryosphere Changes?
Satellite Gravity
Satellite Altimetry
Proxy records
Tide Gauges
ICE SHEET OBSERVATIONS
SEA-LEVEL OBSERVATIONS
Airborne Altimetry
Synthetic Aperture Radar (InSAR)
Satellite Altimetry
Satellite Gravity
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How Sensitive are GIA Contributions to Altimetry
and GRACE Observations to Differences in Current
Ice Models?

• Adopt a few different ice models for Antarctic
  and Greenland and predict present-day crustal
  uplift and geoid rate signals.
• Consider only the on-going viscous Earth
  response to past variations of these ice sheets.
• Influence of Earth model uncertainty is not
  considered.

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Summary

• Solid Earth motion associated with past
  ice-ocean mass flux is a significant contaminant
  signal in observations related to sea-level
  changes (GRACE, tide gauges and proxy records,
  Satellite Altimetry) and cryosphere changes
  (Altimetry and GRACE).
• The accuracy of the climate signal inferred from
  these observations therefore depends on the
  accuracy of the GIA model correction.
• The correction applied is sensitive to the
  adopted ice history and Earth viscosity model.

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Recommendations

• GIA community
• - Make predictions available (data correction
  and site selection)
• - Continue to improve and refine Earth and
  ice components of model
• User community
• - Employ well-calibrated regional models if
  possible or
• - Use a suite of model predictions
• - Use measurements of crustal motion