, Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56...
Transcript of , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56...
![Page 1: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/1.jpg)
Matt King1,3, Grace Nield1, Valentina Barletta2, Andrea Bordoni2, Pippa Whitehouse4, Peter Clarke1 , Eugene Domack5, Ted Scambos6 and Etienne
Berthier7 1 Newcastle University; 2Technical University of Denmark; 3University of Tasmania; 4 Durham University;
5Hamilton College; 6NSIDC; 7CNRS Acknowledgements: COST Action ES0701, Christopher Shuman, Terry Haran and LARISSA project team
![Page 2: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/2.jpg)
Motivation • How is Antarctica responding to
millenial/centennial/decadal scale unloading?
• How can we explain the rapid GPS-observed uplift in the Antarctic Peninsula since ~2002?
• Well observed unloading may provide unique insight into Earth rheology (noting all GIA modelling use linear Maxwell)
1
Motivation Elastic Data Modelling Viscous Local effects Summary
![Page 3: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/3.jpg)
GPS Observations
• Palmer Station 1998 – present
• LARISSA 2009/2010 - present
2
Thomas et al. (2011): elastic response to present day ice mass loss?
Palmer
Motivation Elastic Data Modelling Viscous Local effects Summary
10 years + 3-4 years
![Page 4: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/4.jpg)
Recent Ice Mass Changes Data: • Elevation change from DEM
differencing/ICESat 2003-2008 • Berthier et al., 2012 GRL; Shuman
et al., 2011 J. Glaciology; Scambos et al. (in prep)
3
Larsen A 1995
Larsen B 2002
Prince Gustav 1995
Assumptions for model input: • Ice loss onset few months after
collapse, negligible before this • Mass loss continues at the same
rate to present day • Mass changes away from these
glaciers is constant/long term trend
Motivation Elastic Data Modelling Viscous Local effects Summary
![Page 5: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/5.jpg)
Modelling approach
• Model solid Earth response to ice loss 1995-2013 • Elastic response only? • Low viscosity mantle – viscoelastic response over
~15 years? • Use GPS observed uplift to constrain the
modelling • Make estimate of the background rate • Model – HresV2 - Barletta et al., 2006 (GRL)
4
Motivation Elastic Data Modelling Viscous Local effects Summary
![Page 6: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/6.jpg)
Elastic Model - PREM
5
Need 4 times best estimate ice loss to reproduce uplift
Palmer
Motivation Elastic Data Modelling Viscous Local effects Summary
![Page 7: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/7.jpg)
Elastic Model – 2011 uplift rates
6
Palmer Modelled: 2.23 mm/yr Observed: 6.56 mm/yr
Motivation Elastic Data Modelling Viscous Local effects Summary
Modelled to spherical harmonic degree 3754
![Page 8: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/8.jpg)
Viscoelastic Model • Model a viscous component • Compute RMS misfit between
modelled time series (elastic+viscous+background) and Palmer timeseries
• Incompressible Earth, with further compressible estimates shown as inset – shifts +10 to +15km
7
Motivation Elastic Data Modelling Viscous Local effects Summary
Layer Depth to base (km) Viscosity (Pa s)
Lithosphere 20 – 160 1 x 1051
Upper Mantle 400 1 x 1017 – 1 x 1020
Transition Zone
670 4 x 1020(no sensitivity)
Lower Mantle - 1 x 1022 (no sensitivity)
Best fit with Palmer GPS
Ivins et al 2011
95% CI
![Page 9: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/9.jpg)
Uplift rates for best model
8
Pre-1995 background rate = -2.5 mm/yr
Elastic
Viscous
Visco-elastic + background rate
Motivation Elastic Data Modelling Viscous Local effects Summary
Viscous
![Page 10: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/10.jpg)
Modelled vs. GPS uplift time series
9
PALM
Motivation Elastic Data Modelling Viscous Local effects Summary
Larsen B break-up
Present study Ivins et al 2011 Earth model VM2 Earth model
![Page 11: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/11.jpg)
Uplift residuals
10
Motivation Elastic Data Modelling Viscous Local effects Summary
Site GPS Observed Uplift (mm/yr)
Viscoelastic Modelled Uplift
(mm/yr)
Residual (GPS minus viscoelastic model)
(mm/yr)
PALM 6.56 ± 1.07
(using 2009.0 to 2013.0)
7.77 -1.21 ± 1.07
CAPF 4.50 ± 1.45 7.09 -2.60± 1.45
DUPT 12.84 ± 1.06 10.08 2.76± 1.06
FONP 14.89 ± 1.35 15.98 -1.08± 1.35
HUGO 1.69 ± 1.66 2.82 -1.13± 1.66
ROBI 7.79 ± 1.45 9.52 -1.73± 1.45
VNAD 5.78 ± 1.21 5.77 0.01± 1.21
![Page 12: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/12.jpg)
Viscoelastic Model
11
Motivation Elastic Data Modelling Viscous Local effects Summary
Best fit with Palmer GPS
Best fit with all GPS
![Page 13: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/13.jpg)
Local time-variable elastic effects? • SMB anomalies may cause an additional elastic effect. • Test using RACMO2.1/ANT (Lenaerts et al., 2012) SMB,
anomaly to 1979 - 2011.0 mean
12
Palmer
Motivation Elastic Data Modelling Viscous Local effects Summary
![Page 14: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/14.jpg)
Summary • A unique experiment – needs to be ongoing [dh/dt and new
GPS to capture before/after future events e.g., SCAR inlet] • Elastic response alone cannot explain the observed uplift &
viscous component is required • Modelling suggests the range of parameters that fit the
GPS observations are: • Lithospheric thickness: ~70-135km • Upper mantle viscosity: < 2 x 1018 Pa s
• Pre-2002 uplift at PALM very low. Pre-1995 uplift likely negative [-2.5mm/yr]
• Earth models of Peltier (VM2) and Ivins et al 2011 do not provide good fits to the GPS when combined with post-1995 unloading – is time-dependent rheology at play?
13
Motivation Elastic Data Modelling Viscous Local effects Summary
![Page 15: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/15.jpg)
Rapid viscous uplift and WAIS Gomez et al 2012 highlighted importance of
viscoelastic (blue) response to reverse slope beds (β= slope m/km) cf not considering (green)
Elastic component (red) dominates for first several centuries
![Page 16: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/16.jpg)
Rapid viscous response and grounding line stabilisation But Gomez et al adopted globally typical ηUM=5x1020Pa s (tm=236y) and elastic lithosphere 120km
Weaker Earth model may apply in WAIS, possibly locally very weak
Examine PIG-like scenario – 80x20km region thinning at 2m/yr from t=0 & ongoing
Semi-infinite half-space with elastic lid of 50km and various η and linear and power-law within RELAX
![Page 17: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/17.jpg)
Rapid viscous response and grounding line stabilisation
Weak Earth could result in ~50% greater bedrock adjustment within years to decades cf elastic or high viscosity model
not shown: Power-law rheology concentrates uplift temporally (effective viscosity reduction) and spatially near to load change so important for bedrock slopes
Uplift in centre of load
![Page 18: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/18.jpg)
Joint geophysical and petrological models for the lithosphere structure of the Antarctic Peninsula continental margin
Geophysical Journal International Volume 184, Issue 1, pages 90-110, 30 NOV 2010 DOI: 10.1111/j.1365-246X.2010.04867.x http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.2010.04867.x/full#f7
![Page 19: , Grace Nield 1, Valentina Barletta , Andrea Bordoni ... · Modelled: 2.23 mm/yr Observed: 6.56 mm/yr Motivation Data Modelling Elastic Viscous Local effects Summary Modelled to spherical](https://reader033.fdocuments.net/reader033/viewer/2022051917/600934e8f271856f2474418b/html5/thumbnails/19.jpg)
Joint geophysical and petrological models for the lithosphere structure of the Antarctic Peninsula continental margin
Geophysical Journal International Volume 184, Issue 1, pages 90-110, 30 NOV 2010 DOI: 10.1111/j.1365-246X.2010.04867.x http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.2010.04867.x/full#f12