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Geodetic signatures of glacial changes in Antarctica

Geodetic signatures of glacial changes in Antarctica. Ingo Sasgen Supervision: Detlef Wolf, Zden ě k Martinec GeoForschungsZentrum Potsdam Email: sasgen@gfz-potsdam.de. Larsen B ice-shelf collapse. Jan. 31 – Mar. 05, 2002. National Snow and Ice Data Center, http://nsidc.gov (2005).

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Geodetic signatures of glacial changes in Antarctica

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  1. Geodetic signaturesof glacial changes in Antarctica Ingo Sasgen Supervision: Detlef Wolf, Zdeněk Martinec GeoForschungsZentrum Potsdam Email: sasgen@gfz-potsdam.de MAGMA Seminar, May 25, 2005, Prague

  2. Larsen B ice-shelf collapse Jan. 31 – Mar. 05, 2002 National Snow and Ice DataCenter, http://nsidc.gov (2005) MAGMA Seminar, May 25, 2005, Prague

  3. Causes and consequences of collapse • mean temperature trend of +1.2°C in 100 a for all Antarctic stations • regional warming of +2.5°C in 50 a along the Antarctic Peninsula • warming likely cause for collapse of the Larsen B ice shelf • glacier acceleration observed after desintegration of the Larsen B ice shelf, i.e. ice-velocity increase by factor of 5 to 8 MAGMA Seminar, May 25, 2005, Prague

  4. Scientific importance • Antarctic ice sheet (AIS) largest ice mass on earth • 10 times larger than the Greenland ice sheet • glacial variations closely linked to global climate and sea-level changes • knowledge on present-day state and near-future developement improves climate models, which • predict global temperature and sea-level changes for the centuries to come MAGMA Seminar, May 25, 2005, Prague

  5. Antarctic ice sheet • 13.6 x 106 km2 grounded portion,i.e. 95 % of the continent • volume of 61 m equivalent sea level (ESL) • ~ 4 km maximum ice thickness • drained by ice streams which feed ice shelves • mountain glaciers alongAntarcic Peninsula MAGMA Seminar, May 25, 2005, Prague

  6. Ice sheet volume changes • accumulation: ~ + 5 mm ESL/a • accumulation – discharge: ~ - 0.1 mm ESL/a • discharge since last glacial maximum (LGM),21 ka BP: ~ -12 m ESL • present sea-level rise: ~ 1.8 mm/a ESL • sea-level rise since LGM: ~ 110 m ESL MAGMA Seminar, May 25, 2005, Prague

  7. Antarctic continent • area of rock outcrops < 0.4 % • East Antarctica is a Precambrian shield • West Antarctica comprises younger, tectonically more active terranes MAGMA Seminar, May 25, 2005, Prague

  8. Transantarctic Mountains Transantarctic Mountains Transantarctic Mountains mark tectonic suture zone lateral variations of the lithosphere thickness and the viscosity expected MAGMA Seminar, May 25, 2005, Prague

  9. Geoid-height change Radial displacement Modelling components Load model Last glaciation~ 1000 a Seasonal~ 1 a Secluar~ 10 – 100 a Earth model Elastic Viscoelastic Global PositioningSystem (GPS) Gravity Recovery andClimate Experiment (GRACE) Earth response MAGMA Seminar, May 25, 2005, Prague

  10. Seasonal ice-mass changes (VAUG) Vaughan et al. (1999) Cazenave et al. (2000) • accumulation of ~ 5 mm ESL/a based on ice cores • temporal variation from global mean sea-level changes inferred from satellite altimetry MAGMA Seminar, May 25, 2005, Prague

  11. Seasonal earth response Elastic, cut-off degree 256 Geoid-height change Radial displacement MAGMA Seminar, May 25, 2005, Prague

  12. Secular ice-mass balance (RT02) Rignot & Thomas (2002) Update 2004: East Antarctica roughly in balance most prominent changes of up to 1 m/a for glaciers draining into the Amundsen Sea (PIG, THW, SMI, KOH) East Antarctica in balance Byrd (BYR) likely in balance (former 0.05 mm ESL/a) ice-thickness changes along Antarctic Peninsula and West Antarctic coast several m/a MAGMA Seminar, May 25, 2005, Prague

  13. Earth response to secular changes Elastic, cut-off degree 256 Geoid-height change Radial displacement MAGMA Seminar, May 25, 2005, Prague

  14. Viscoelastic earth model present-day post-glacial rebound (PGR) due tolast glaciation is calculated with a lateral homogenous viscoelastic earth model based on the spectral-finite element code developed by Martinec (2000) MAGMA Seminar, May 25, 2005, Prague

  15. Earth model parameters WestAntarctica East Antarctica MAGMA Seminar, May 25, 2005, Prague

  16. 15 ka BP 7 ka BP 4 ka BP Last glaciation and its retreat (HUY) Huybrechts (2002) thermomechanical model allows regional retreat history, e. g. late retreat from the Ronne ice shelf ice volume of – 12 m ESL at the LGM compared to present day MAGMA Seminar, May 25, 2005, Prague

  17. Earth response to last glaciation Viscoelastic, cut-off degree 256 Geoid-height change Radial displacement MAGMA Seminar, May 25, 2005, Prague

  18. International GPS Service stations • 7 stations along the Antarcic coast • continuous time series > 6 a • nominal accuracy ~ 1 mm/a MAGMA Seminar, May 25, 2005, Prague

  19. Land-uplift rates at GPS stations mm/a mm/a MAGMA Seminar, May 25, 2005, Prague

  20. Possible GPS transects • GPS measurements along A-A‘, B-B1 and B1-B2 can constrain the glacial history • Measurements along B2-B questionable: tectonic displacements large and influenced by rheological transition MAGMA Seminar, May 25, 2005, Prague

  21. Summary of GPS comparison Interpretation of IGS data difficult, because stations located • at rheological transition (e.g. Mawson, Davis) lateral heterogenous earth model • at ice margin where rebound is complex accurate last glaciation models • in tectonically active regions (e.g. Mc Murdo) ignore particular station • not in the former load center Large solution differencesbetween  regional networks, e.g. Amery ice shelf region MAGMA Seminar, May 25, 2005, Prague

  22. GRACE satellite mission MAGMA Seminar, May 25, 2005, Prague

  23. GRACE satellite mission • Primary mission objective of the GRACE:monthly high-accuracy determination of the earth‘s gravity field,i.e. temporal variations of the geoid height • Possible application:mass balance of ice sheetsocean-current changespost-glacial rebound • Mission status:operational since October 200218 monthly solutions existcurrent spatial resolution ~ 1000 km with anestimated accuracy ~ mm/a MAGMA Seminar, May 25, 2005, Prague

  24. Schematic principle of GRACE GPS GPS GPS GPS Precise orbitdetermination by GPS Satellite A Satellite B Satellite B Satellite-satellite distance ∆l tracked by microwave link ∆m ∆l = f (∆m) MAGMA Seminar, May 25, 2005, Prague

  25. May. 2003 – Apr. 2003 May 2003 – Apr. 2002 Nov. 2002 – Aug. 2002 Comparison of spectral geoid change Nov. 2003 – Nov. 2002 MAGMA Seminar, May 25, 2005, Prague

  26. Spatial geoid change comparison Aug. 2003 – Aug. 2002 May 2003 – Apr. 2003 Nov. 2002 – Aug. 2002 Prediction, cut-off degree 13 Observation, cut-off degree 13 MAGMA Seminar, May 25, 2005, Prague

  27. Discussion of geoid-height interpretation Predicted and GRACE measured geoid changes do not correspond yet: • Strong anomalies over the ocean dominate the signal artificial ocean phenomenon: tides not successfully removed? real ocean phenonmenon: circumpolar current? • Seasonal changes not visible (not even the sign) temporal variation not realistic? • Secular changes not detectable at the current resolution expected 8 a of measurments sufficient for a linear-tend estimate? MAGMA Seminar, May 25, 2005, Prague

  28. accumulation • discharge Outlook: seasonal ice-mass changes Include metereological parameters • accumulation from moisture flux onto the Antarctic continent • discharge, i.e. mainly calving, from surface-air temperature • Patagonia as proxy for the Antarctic Peninsula? MAGMA Seminar, May 25, 2005, Prague

  29. Outlook: GRACE data May 2003 – May 2002 minus Aug. 2003 – Aug. 2002 • Quantify errors introduced by ocean model • Remove ocean signal (e.g. by filtering) • Focus on (regional) total ice-mass changes, not spatial distribution • Allow error dependent weighing of degree power to include maximum information MAGMA Seminar, May 25, 2005, Prague

  30. Summary Glacial changes of the AIS induce geoid changes and land uplift : with measurable magnitudes and specific signatures Observations by GRACE and GPS  do not correspond to the predictions yet  need to be refined and extended according to the expected signature MAGMA Seminar, May 25, 2005, Prague

  31. Questions ?!!?! ??? X MAGMA Seminar, May 25, 2005, Prague

  32. Glacial changes of the AIS induce geoid and surface displacement changes: with measurable magnitudes and specific signatures Observations of the geoid (GRACE) and the surface displacement changes (GPS)  do not correspond to the predictions yet  need to be refined and extended according to the expected signature MAGMA Seminar, May 25, 2005, Prague

  33. Present ice-mass balance (updated) Rignot & Thomas (2002), Thomas et al. (2004), Rignot et al. (2004) Sasgen et al. (2005) MAGMA Seminar, May 25, 2005, Prague

  34. Secular Spectral geoid change Last glaciation • Secular ice-mass balance induces geoid change well above GRACE accuracy • High power even at high degrees • However, seasonal changes ~ one order of magnitude larger • Interannual variation can introduce „pseudo“-secular trend • Last glaciation induces high power at degree low degrees well above the GRACE accuracy • Up to degree 9 the employed earth model is not importance MAGMA Seminar, May 25, 2005, Prague

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