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

Edited version: original slides 12-19 removed. Glacial Isostatic Adjustment Contributions to Tide Gauge, Altimetry and GRACE Observations. Glenn Milne Dept of Earth Sciences University of Durham, UK.

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

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  1. Edited version: original slides 12-19 removed Glacial Isostatic Adjustment Contributions to Tide Gauge, Altimetry and GRACE Observations Glenn Milne Dept of Earth Sciences University of Durham, UK Contributors: Mark Tamisiea, Konstantin Latychev, Erik Ivins, Philippe Huybrechts, Jerry Mitrovica, Bert Vermeersen.

  2. http://www.ngdc.noaa.gov/paleo/slides/slideset/index11.htm

  3. 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

  4. 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

  5. GIA Response: Driven by Contemporary and Past Mass Flux Tamisiea et al., 2003

  6. How Can the GIA Community Contribute to a Better Understanding of Recent Sea-Level Changes? Ice-ocean mass exchange Ocean warming Anthropogenic effects Climate change Tide Gauges Proxy records SEA-LEVEL FORCINGS SEA-LEVEL OBSERVATIONS Ocean dynamics Solid Earth motion Satellite Altimetry Satellite Gravity Ocean-atmosphere interaction

  7. Viscous “Memory” of Solid Earth to Past Ice-Ocean Mass Flux

  8. A B Mitrovica and Milne (2002)

  9. 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.

  10. Employ Careful Selection Criteria to Minimise Influence of Solid Earth Motion Douglas, 1997

  11. SLR=1.5±0.1 mm/yr SLRGIA=1.8±0.1 mm/yr I I

  12. 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

  13. GIA Contribution to Observations of Recent Cryosphere Changes? Satellite Altimetry Satellite Gravity Tide Gauges Proxy records ICE SHEET OBSERVATIONS SEA-LEVEL OBSERVATIONS Airborne Altimetry Synthetic Aperture Radar (InSAR) Satellite Altimetry Satellite Gravity

  14. 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.

  15. 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.

  16. 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

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