I. Sasgen et al. MAGMA Seminar, May 25, 2005, Prague Geodetic signatures of glacial changes in Antarctica Ingo Sasgen Supervision: Detlef Wolf, Zdeněk Martinec GeoForschungsZentrum Potsdam

Geodetic signatures of AntarcticaI. Sasgen Page 2 MAGMA Seminar, May 25, 2005, Prague Larsen B ice-shelf collapse National Snow and Ice Data Center, (2005) Jan. 31 – Mar. 05, 2002

Geodetic signatures of AntarcticaI. Sasgen Page 3 MAGMA Seminar, May 25, 2005, Prague 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

Geodetic signatures of AntarcticaI. Sasgen Page 4 MAGMA Seminar, May 25, 2005, Prague 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

Geodetic signatures of AntarcticaI. Sasgen Page 5 MAGMA Seminar, May 25, 2005, Prague Antarctic ice sheet  13.6 x 10 6 km 2 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 along Antarcic Peninsula

Geodetic signatures of AntarcticaI. Sasgen Page 6 MAGMA Seminar, May 25, 2005, Prague Ice sheet volume changes  accumulation: ~ + 5 mm ESL/a  accumulation – discharge: ~ 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

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

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

Geodetic signatures of AntarcticaI. Sasgen Page 9 MAGMA Seminar, May 25, 2005, Prague Modelling components Elastic Last glaciation ~ 1000 a Seasonal ~ 1 a Secluar ~ 10 – 100 a Viscoelastic Geoid-height change Radial displacement Gravity Recovery and Climate Experiment (GRACE) Global Positioning System (GPS) Load model Earth model Earth response

Geodetic signatures of AntarcticaI. Sasgen Page 10 MAGMA Seminar, May 25, 2005, Prague 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

Geodetic signatures of AntarcticaI. Sasgen Page 11 MAGMA Seminar, May 25, 2005, Prague Seasonal earth response Geoid-height change Radial displacement Elastic, cut-off degree 256

Geodetic signatures of AntarcticaI. Sasgen Page 12 MAGMA Seminar, May 25, 2005, Prague  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 Update 2004: Secular ice-mass balance (RT02) Rignot & Thomas (2002)

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

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

Geodetic signatures of AntarcticaI. Sasgen Page 15 MAGMA Seminar, May 25, 2005, Prague Earth model parameters West Antarctica East Antarctica

Geodetic signatures of AntarcticaI. Sasgen Page 16 MAGMA Seminar, May 25, 2005, Prague 15 ka BP7 ka BP4 ka BP Last glaciation and its retreat (HUY)  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 Huybrechts (2002)

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

Geodetic signatures of AntarcticaI. Sasgen Page 18 MAGMA Seminar, May 25, 2005, Prague International GPS Service stations  7 stations along the Antarcic coast  continuous time series > 6 a  nominal accuracy ~ 1 mm/a

Geodetic signatures of AntarcticaI. Sasgen Page 19 MAGMA Seminar, May 25, 2005, Prague Land-uplift rates at GPS stations mm/a

Geodetic signatures of AntarcticaI. Sasgen Page 20 MAGMA Seminar, May 25, 2005, Prague 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

Geodetic signatures of AntarcticaI. Sasgen Page 21 MAGMA Seminar, May 25, 2005, Prague 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 differences between  regional networks, e.g. Amery ice shelf region

Geodetic signatures of AntarcticaI. Sasgen Page 22 MAGMA Seminar, May 25, 2005, Prague GRACE satellite mission

Geodetic signatures of AntarcticaI. Sasgen Page 23 MAGMA Seminar, May 25, 2005, Prague 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 sheets ocean-current changes post-glacial rebound  Mission status: operational since October monthly solutions exist current spatial resolution ~ 1000 km with an estimated accuracy ~ mm/a

Geodetic signatures of AntarcticaI. Sasgen Page 24 MAGMA Seminar, May 25, 2005, Prague Schematic principle of GRACE Satellite ASatellite B ∆m Satellite-satellite distance ∆l tracked by microwave link Satellite B ∆l = f (∆m) GPS Precise orbit determination by GPS

Geodetic signatures of AntarcticaI. Sasgen Page 25 MAGMA Seminar, May 25, 2005, Prague May – Apr. 2003May 2003 – Apr. 2002Nov – Aug Comparison of spectral geoid change Nov – Nov. 2002

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

Geodetic signatures of AntarcticaI. Sasgen Page 27 MAGMA Seminar, May 25, 2005, Prague 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?

Geodetic signatures of AntarcticaI. Sasgen Page 28 MAGMA Seminar, May 25, 2005, Prague 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?  accumulation  discharge

Geodetic signatures of AntarcticaI. Sasgen Page 29 MAGMA Seminar, May 25, 2005, Prague Outlook: GRACE data  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 May 2003 – May 2002 minus Aug – Aug. 2002

Geodetic signatures of AntarcticaI. Sasgen Page 30 MAGMA Seminar, May 25, 2005, Prague  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 Summary

Geodetic signatures of AntarcticaI. Sasgen Page 31 MAGMA Seminar, May 25, 2005, Prague Questions ??? X ?!!?!

Geodetic signatures of AntarcticaI. Sasgen Page 32 MAGMA Seminar, May 25, 2005, Prague  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

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

Geodetic signatures of AntarcticaI. Sasgen Page 34 MAGMA Seminar, May 25, 2005, Prague 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