1. Page 1 ESA CliC workshop, Tromsø, 20 January 2015 Ingo Sasgen& REGINA consortium www.regina-science.eu (Mark Drinkwater, ESA); V. Klemann, L. Petrie, P. Clarke, N. Schön, J. L. Bamber, R. Pail, M. Horwath, A. Horvath STSE CryoSat+ Cryosphere Study Regional glacial isostatic adjustment and CryoSat elevation rate corrections in Antarctica (REGINA) Contract-Nr.: 4000107393/12/I-NB Contact: sasgen@gfz-potsdam.de REGINA (www.regina-science.eu): Ingo Sasgen (PI), Martin Horwath, Volker Klemann, Elizabeth J. Petrie, Nana Schoen, Roland Pail, Alexander Horvath, Jonathan L. Bamber, Peter J. Clarke, Hannes Konrad and Mark R. Drinkwater (ESA)

2. Page 2 ESA CliC workshop, Tromsø, 20 January 2015 Glacial-isostatic adjustment

3. Page 3 ESA CliC workshop, Tromsø, 20 January 2015 Ice sheet Bedrock Ocean Shelf Glacial-isostatic adjustment (GIA) Flow-line GIA simulation, example [1] Hannes Konrad, Ingo Sasgen, Volker Klemann (GFZ)

4. Page 4 ESA CliC workshop, Tromsø, 20 January 2015 Approaching GIA in Antarctica Hybrid GIA estimate Numerical modelling Earth / Ice models, Paleo observations etc. Earth observation GPS, GRACE, Altimetry GIA estimateGIA prediction e.g. Whitehouse et al. 2012 Ivins & James 2005 (“IMBIE-models”) e.g. Riva et al. 2009, Gunter et al. 2014 Sasgen et al. 2013 REGINA aims: Determine GIA elevation rate correction for CryoSat-2 Investigate Crustal Low Viscosity Zone Employ multiple space-geodetic data sets

5. Page 5 ESA CliC workshop, Tromsø, 20 January 2015 Present and past ice-mass change Accumulation event Deglaciation since LGM

6. Page 6 ESA CliC workshop, Tromsø, 20 January 2015 Observation equations System of linear equations GRACE GPS ICESat/Env. Present mass change Past mass change Compaction (density ch.) Kernels*: Ice-elevation change Gravitational potential Bedrock displacement ElasticViscous Satellite observations Earth response * Filtered according to observation Consideration of Earth structures & Filtering Reprocessed data Solution with discs on geodesic grid

7. Page 7 ESA CliC workshop, Tromsø, 20 January 2015 Altimetry ICESat / Envisat combination for 2003-2009 [1] Combination mask ICESat available only ICESat (smaller errors) Envisat (smaller errors) N. Schön, J. Bamber, Univ. Bristol 10 km gridded data

8. Page 8 ESA CliC workshop, Tromsø, 20 January 2015 Gravimetry A. Horvath, R. Pail (TU München), M. Horwath (TU Dresden)

9. Page 9 ESA CliC workshop, Tromsø, 20 January 2015 GPS displacements available unavailable partially available [1] L. Petrie (now Univ. Glasgow), P. Clarke (Newcastle Univ.) Trend estimation accounting for colored noise Review of metadata Test of processing options

10. Page 10 ESA CliC workshop, Tromsø, 20 January 2015 Geometrical set-up Shear velocity anomalies [1] with respect to PREM [2] Spatial distribution of discs East Ant. Rheology (200 km Elast. lith.) West Ant. Rheology (variable) 1175 discs Deviation (%) [1] Danesi & Morelli (2001); [2] Dziewonski & Anderson (1981) Earth structure dependent response kernels [3] [3] V. Klemann, I. Sasgen (GFZ) Possibility: GOCE constraints

11. Page 11 ESA CliC workshop, Tromsø, 20 January 2015 Step 1: first-order GIA estimate Removal of surface-mass contributions GRACE [1] Altimetry [1] [1] Post-processing I: Swenson & Wahr, 2006 + Gaussian 200 km (GFZ RL05) = Different scale

12. Page 12 ESA CliC workshop, Tromsø, 20 January 2015 GIA estimate for Antarctica

13. Page 13 ESA CliC workshop, Tromsø, 20 January 2015 Influence of Earth structure WeakStrong Weak+Filtering IMBIE

14. Page 14 ESA CliC workshop, Tromsø, 20 January 2015 Separation of ice mass and GIA Ice-mass balance 2003-2009 GIA estimate

15. Page 15 ESA CliC workshop, Tromsø, 20 January 2015 GIA apparent mass change (selection) But again: spread GIA corrections > GRACE signal REGINA 2003-2008: -63 to -75 Gt/yr (IMBIE: -72 Gt/yr)

16. Page 16 ESA CliC workshop, Tromsø, 20 January 2015 IOM validation of REGINA estimates IOM [1] mass balance:− 66 Gt/yr (c.f. Rignot, IOM-IMBIE: −142 Gt/yr) [1] Depoorter, M. A., J. L. Bamber, J. A. Griggs, J. T. M. Lenaerts, S. R. M. Ligtenberg, M. R. van den Broeke, and G. Moholdt (2013), Calving fluxes and basal melt rates of Antarctic ice shelves, Nature, 502(7469), 89-92. REGINA mass balance: − 63 to -75 Gt/yr (Envisat/ICESat & GRACE combination)

17. Page 17 ESA CliC workshop, Tromsø, 20 January 2015 REGINA Phase 1 conclusions Combination algorithm Includes GRACE, Envisat/ICESat, GPS Accounts for different filtering / resolutions Solves for local density changes (no a priori model req.) Refined Earth structure considers Crustal low-viscosity zone East and West Antarctic rheology Low mantle viscosities (beyond IMBIE range; not shown) Results GIA apparent mass change of 26 to 38 Gt/yr Ice-mass balance of −63 to −75 Gt/yr (IMBIE –72 Gt/yr) Next steps: final GIA product in REGINA Phase 2 (08/2015)

18. Page 18 ESA CliC workshop, Tromsø, 20 January 2015 www.regina-science.eu

19. Page 19 ESA CliC workshop, Tromsø, 20 January 2015 Apparent mass change of GIA IMBIE (not used)IMBIE (used)Post IMBIE GIA correction ICE-5GIJ05_R2W12aAGE1REGINAICE-6GIJ05_R2_5k Type Numerical prediction Geodetic estimate Numerical prediction Data set used Geomorphology, Paleoclimate, relative sea-level data (GIA) Geomorphology, Paleoclimate Ice-dynamics, Paleoclimate, geomorphology, relative sea-level data (GIA) GPS, GIA ensemble modelling ICESat/Envisa t, GRACE, GPS, GIA kernels Geomorphology, Paleoclimate, relative sea-level data (GIA) Geomorphology, Paleoclimate Spatial resolution (SH degree) provided -2566012096-256 Earth model assumptions Yes (implicit)Yes No Yes (implicit)Yes Reference Sasgen et al. 2013; doi:10.5194/tcd- 6-3703-2012 Ivins et al. 2013; doi:10.1002/jgrb.50 208 Whitehouse et al. 2012b; doi:10.1111/j.1365- 246X.2012.05557.x Sasgen et al. 2013; doi:10.5194/tcd- 6-3703-2012 www.regina- science.eu Argus et al. 2014; doi: 10.1093/gji/ggu14 0 Velicogna et al. AGU 2014, G51A-0343 Apparent mass change (Gt/yr) 140 to 18040 to 65ca. 604926 to 38107ca. 120 GRACE minus REGINA GIA, 2003-2008 GRACE minus REGINA GIA, 2003-2014 -63 to -75 Gt/yr (IMBIE: -72 Gt/yr) -100 to -112 Gt/yr

20. Page 20 ESA CliC workshop, Tromsø, 20 January 2015 CSR RL05 ICESat CSR RL05 @ ICESat CSR RL05 & ICESat [selected] Data availability Too noisy for GRACE Best Additional signals

21. Page 21 ESA CliC workshop, Tromsø, 20 January 2015 Geoid rate (e’) to disc load h l =90 km (thick) µ Ast. = 1 10 18 Pa s (weak) Load + Elastic response Load + viscoelastic response Relaxation, without load J max =2048 (Model) Load + Elastic response Relaxation, without load Each line: response after +Δt = 10 yrs; Sim. period: 2 kyrs

22. Page 22 ESA CliC workshop, Tromsø, 20 January 2015 Displacement rate (u’) to disc load Elastic response Viscoelastic response Relaxation, without loading Each line: response after +Δt = 10 yrs; Sim. period: 2 kyrs Load dimension Elastic response Relaxation, without loading h l =90 km (thick) µ Ast. = 1 10 18 Pa s (weak)

23. Page 23 ESA CliC workshop, Tromsø, 20 January 2015 Separation ice-mass and GIA (geoid) Filter 2: Statistical filter + Wiener filter Filter 1: REGINA Present-day ice-mass change GIA

24. Page 24 ESA CliC workshop, Tromsø, 20 January 2015 Radial displacement rate for disc load 3x10 19 Pa s (stiff) 90 km 3x10 19 Pa s (stiff) 30 km (strong) (weak) V. Klemann, I. Sasgen, GFZ Weaker lithosphere  more localized & greater amplitudes Viscosity not important within REGINA context “standard” West Antarctica “weak” West Antarctica Mention paper: GOCE

25. Page 25 ESA CliC workshop, Tromsø, 20 January 2015 Procedure of separation

26. Page 26 ESA CliC workshop, Tromsø, 20 January 2015 Step 2: Refinement with GPS

27. Page 27 ESA CliC workshop, Tromsø, 20 January 2015 Step 2: Refinement with GPS Viscous response (past loading) Elastic response (present loading) East Ant. rheol. West Ant. rheol. J max =2048 J max = 90 & 200 km Gaussian

28. Page 28 ESA CliC workshop, Tromsø, 20 January 2015 GRACE e’ vs. GPS u’ (Altim. removed) East Ant. rheol. West Ant. rheol.

29. Page 29 ESA CliC workshop, Tromsø, 20 January 2015 Elastic and viscoelastic kernels Axisymmetric disc load: 62 km radius, mass gain 5.6 Gt/yr Temporal evolution J max =2048 ~ 10 km Radius constant Load rate constant Viscoelastic Earth model: Martinec, 2000 V. Klemann, I. Sasgen, GFZ