REGINA presentation

Ingo Sasgen& REGINA consortium

www.regina-science.eu (Mark Drinkwater, ESA); V. Klemann, L. Petrie, P. Clarke, N. Schn, J. L. Bamber, R. Pail, M. Horwath, A. Horvath

STSE CryoSat+ Cryosphere StudyRegional glacial isostatic adjustment andCryoSat elevation rate corrections in Antarctica(REGINA)Contract-Nr.: 4000107393/12/I-NBContact: 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)Page Nr.ESA CliC workshop, Troms, 20 January 20151Glacial-isostatic adjustment

Page Nr.ESA CliC workshop, Troms, 20 January 20152Glacial-isostatic adjsutment describes how the Earth deforms under the pressure of a ice sheet and then returns to the its initial condition after melting of the ice.For example, during the last glacial-maximum about 20 ka BP, North America covered by ice of about 4 km thicknessThese surface loads deformed the lithosphere several hundred meters downward.After melting of the ice sheet Earth started to rebounded. Since its mantle acts like a high viscous liquid, this process is strongly delayed and still ongoing. It is visible today as land uplfit measureable by GPSBut GIA also represents a large signal in the GRACE data as due to the inflow of mantle material to the formerly glaciated regions.Modelling of the GIA signal is done with viscoelastic earth models.

Ice sheetBedrockOceanShelfGlacial-isostatic adjustment (GIA)Flow-line GIA simulation, example[1] Hannes Konrad, Ingo Sasgen, Volker Klemann (GFZ)Page Nr.ESA CliC workshop, Troms, 20 January 20153Approaching GIA in AntarcticaHybrid GIA estimate

Numerical modellingEarth / Ice models, Paleo observations etc. Earth observationGPS, GRACE, AltimetryGIA estimateGIA predictione.g. Whitehouse et al. 2012Ivins & James 2005(IMBIE-models)e.g. Riva et al. 2009, Gunter et al. 2014Sasgen et al. 2013

REGINA aims:Determine GIA elevation rate correction for CryoSat-2Investigate Crustal Low Viscosity ZoneEmploy multiple space-geodetic data setsPage Nr.ESA CliC workshop, Troms, 20 January 2015Two principal approaches towards determining GIA in Antarctica1) Numerical modelling; thermomechanical ice sheet models, viscoelastic Earth models, constraints: geomorphological data, relative sea-level, Paleoclimate, etx.2) Geodetic estimate: separate GIA and ice-mass balance by the different signatures in the geodetic data sets. Gunter et al. 2014, altimetry + gravimetry but without GPSMix of both approaches Way forward

Present and past ice-mass change Accumulation eventDeglaciation since LGMPage Nr.ESA CliC workshop, Troms, 20 January 2015Conceptual separation of ongoing and past ice-mass change.Present-day: i.e. occurring during measurement period. e.g. accumulation event: mass increase increase in gravitational potential (GRACE), increase in ice sheet surface elevation (altimetry) and subsidence of bedrock (GPS)Past, i.e. occurring before the time of measurement. But signature in observations due to delayed Earth response. Loading relevant for few hundred to thousands of years, depending on viscosity of the Earth mantle.

Some GRACE and GPS complementary w.r.t. present-day and past ice-mass change. Therefore great for separation.Observation equationsSystem of linear equationsGRACEGPSICESat/Env.Present mass changePast mass changeCompaction (density ch.)Kernels*:Ice-elevation changeGravitational potential Bedrock displacement

ElasticViscousSatellite observationsEarth response* Filtered according to observationConsideration of Earth structures & FilteringReprocessed dataSolution with discs on geodesic gridPage Nr.ESA CliC workshop, Troms, 20 January 2015Response linear w.r.t. load, therefore problem can be formulated as simple system of linear equations. Lefthandside: data sets (individually filtered)Righthandsie: unknowns (present-day ice-mass change, past ice-mass change, and pure density change = no signal in GPS and GRACE)Matrix consists of response functions to individual forcing. Response functions to disc-load functions calculated with viscoelastic Earth modelNext, preparation of data setsAltimetryICESat / Envisat combination for 2003-2009 [1]

Combination maskICESat available onlyICESat (smaller errors)Envisat (smaller errors)

N. Schn, J. Bamber, Univ. Bristol10 km gridded dataPage Nr.ESA CliC workshop, Troms, 20 January 2015Decision for combining Envisat / ICESat based on errors. Get signal at ice sheet margin and tighten polar gap (omission area of radar) Reduces some of the bias of LA within East Antarctica

7Gravimetry

A. Horvath, R. Pail (TU Mnchen), M. Horwath (TU Dresden)Page Nr.ESA CliC workshop, Troms, 20 January 2015GRACE linear trends for time period of ICESatFiltering based on Swenson & Wahr, optimized to effectively reduce noise, while minimizing signal degradation. Monthly error levelsGaussian 200 km smoothing after destriping8GPS displacements

availableunavailablepartially available[1] L. Petrie (now Univ. Glasgow), P. Clarke (Newcastle Univ.)Trend estimation accounting for colored noiseReview of metadataTest of processing optionsPage Nr.ESA CliC workshop, Troms, 20 January 2015Re-analysis of GPS data for AntarcticaReview of metadataTest of processing options (e.g. atmospheric correction)Trend estimation accounting for coloured noise.9

Geometrical set-upShear velocity anomalies[1] with respect to PREM[2]

Spatial distributionof discsEast 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 constraintsPage Nr.ESA CliC workshop, Troms, 20 January 2015Geometric set up showing the placement of the disc response functions in Antarctica. Rheological difference between East and West is considered, as indicated by seismic imagingEast Antarctic rheology fixed. West Antarctic varied to assess influence of Earth structure.Step 1: first-order GIA estimateRemoval of surface-mass contributions

GRACE [1]Altimetry [1]

[1] Post-processing I: Swenson & Wahr, 2006 + Gaussian 200 km (GFZ RL05)=

Different scalePage Nr.ESA CliC workshop, Troms, 20 January 2015First-order GIA estimate.Assumption: all height changes caused by ice in altimetry. Altimetry filtered identical to GRACESubtraction gives first-oder gravity signal of GIA (not bedrock displacement) GIA estimate for Antarctica

Page Nr.ESA CliC workshop, Troms, 20 January 2015Results: Left first order GIA estimate. Right after correction with GPS. Pronounced improvement: Antarctic Peninsula. Signal from altimetry too large positive. Density of ice leads to overestimation of positive mass. Residual signal (GIA) strongly negative. After correction with GPS uplift as expected.

12Influence of Earth structure

WeakStrongWeak+FilteringIMBIEPage Nr.ESA CliC workshop, Troms, 20 January 2015Sensitivity to Earth model. Upper left: extreme case weak lithosphere + ductily layer. GIA gravity changes produce uplift up to 3 cm/yr, locally.Upper right: extreme case thick lithosphere, signature much smoother und only up to 10 mm/yr. Good agreement in magnitude and location with W12a. But differences remainLower left: Same as upper left, but with a posteriorio filtering applied. More robust as inversion for uplift rates can produce artefacts, away from GPS stations

Separation of ice mass and GIAIce-mass balance 2003-2009GIA estimatePage Nr.ESA CliC workshop, Troms, 20 January 2015Approach allows separation of GIA and ice-mass balance. And the components can individually be quantified. As by product ice-mass balanceMass balances next slide14GIA apparent mass change (selection)

But again: spread GIA corrections > GRACE signalREGINA 2003-2008:-63 to -75 Gt/yr (IMBIE: -72 Gt/yr)Page Nr.ESA CliC workshop, Troms, 20 January 2015IOM 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)

Page Nr.ESA CliC workshop, Troms, 20 January 201516REGINA Phase 1 conclusionsCombination algorithmIncludes GRACE, Envisat/ICESat, GPSAccounts for different filtering / resolutionsSolves for local density changes (no a priori model req.)Refined Earth structure considersCrustal low-viscosity zone East and West Antarctic rheologyLow mantle viscosities (beyond IMBIE range; not shown)ResultsGIA apparent mass change of 26 to 38 Gt/yrIce-mass balance of 63 to 75 Gt/yr (IMBIE 72 Gt/yr)Next steps: final GIA product in REGINA Phase 2 (08/2015)

Page Nr.ESA CliC workshop, Troms, 20 January 201517

www.regina-science.eu

Page Nr.ESA CliC workshop, Troms, 20 January 201518Apparent mass change of GIAIMBIE (not used)IMBIE (used)Post IMBIEGIA correctionICE-5GIJ05_R2W12aAGE1REGINAICE-6GIJ05_R2_5kTypeNumerical predictionNumerical predictionNumerical predictionGeodetic estimateGeodetic estimateNumerical predictionNumerical predictionData set usedGeomorphology, Paleoclimate, relative sea-level data (GIA)Geomorphology, PaleoclimateIce-dynamics, Paleoclimate, geomorphology, relative sea-level data (GIA)GPS, GIA ensemble modellingICESat/Envisat, GRACE, GPS, GIA kernelsGeomorphology, Paleoclimate, relative sea-level data (GIA)Geomorphology, PaleoclimateSpatial resolution (SH degree) provided-2566012096-256Earth model assumptionsYes (implicit)YesYesNoNoYes (implicit)YesReferenceSasgen et al. 2013; doi:10.5194/tcd-6-3703-2012Ivins et al. 2013; doi:10.1002/jgrb.50208Whitehouse et al. 2012b; doi:10.1111/j.1365-246X.2012.05557.xSasgen et al. 2013; doi:10.5194/tcd-6-3703-2012www.regina-science.euArgus et al. 2014; doi: 10.1093/gji/ggu140 Velicogna et al. AGU 2014, G51A-0343Apparent mass change (Gt/yr)140 to 18040 to 65ca. 604926 to 38107ca. 120 GRACE minus REGINA GIA, 2003-2008GRACE minus REGINA GIA, 2003-2014-63 to -75 Gt/yr (IMBIE: -72 Gt/yr)-100 to -112 Gt/yrPage Nr.ESA CliC workshop, Troms, 20 January 2015

CSR RL05ICESatCSR RL05@ ICESatCSR RL05& ICESat[selected] Data availabilityToo noisy for GRACEBestAdditional signalsPage Nr.ESA CliC workshop, Troms, 20 January 2015

Geoid rate (e) to disc loadhl=90 km (thick)Ast.= 1 1018 Pa s(weak)

Load + Elastic responseLoad + viscoelastic responseRelaxation, without loadJmax=2048(Model)Load + Elastic responseRelaxation, without loadEach line: response after +t = 10 yrs;Sim. period: 2 kyrsPage Nr.ESA CliC workshop, Troms, 20 January 201521Displacement rate (u) to disc load

Elastic responseViscoelastic responseRelaxation, without loadingEach line: response after +t = 10 yrs;Sim. period: 2 kyrsLoad dimensionElastic responseRelaxation, without loading

hl=90 km (thick)Ast.= 1 1018 Pa s(weak)Page Nr.ESA CliC workshop, Troms, 20 January 2015Each line -> time interval of 10 yr until 2000 yr.Time (ka) -> Time (kyr)

Inversion ohne elastische Lastaenderung und transiente Phase.Dies ist motiviert, da bereits nach < 100 yr der Zustand schon fast relaxiert ist.

22Separation ice-mass and GIA (geoid)

Filter 2:Statistical filter+ Wiener filterFilter 1:REGINAPresent-day ice-mass changeGIAPage Nr.ESA CliC workshop, Troms, 20 January 2015C:\Users\sasgen\Dropbox\cryoitt\deliverable\D5.1 Impact Assessment Report\Apparent_Volume_change.xlsx23Radial displacement rate for disc load

3x1019 Pa s(stiff)90 km 3x1019 Pa s(stiff)30 km(strong)(weak)V. Klemann, I. Sasgen, GFZWeaker lithosphere more localized & greater amplitudes

Viscosity not important within REGINA context standard West Antarcticaweak West AntarcticaMention paper: GOCE Page Nr.ESA CliC workshop, Troms, 20 January 2015These are example response functions. Varied parameters are: thickness of the lithosphere between 30 km (very thin) and 90 km (standard). Also in- and excluding ductile layer (possible thin viscous layer in the elastic lithosphere), further weakening the lithosphere. Viscosity also varied but not important for steady state runs

REMOVE24

Procedure of separation

Page Nr.ESA CliC workshop, Troms, 20 January 2015REMOVE

Step 2: Refinement with GPSPage Nr.ESA CliC workshop, Troms, 20 January 2015Next, correct the first order GIA estimate using GPSWhy should this work?Y-axis: GPS uplift rate corrected for mass change observed with altimetryX-axi

s: Same but GRACE minus altimetry (plot before)

REMOVE 14-1626Step 2: Refinement with GPS

Viscous response(past loading)Viscous response(past loading)Elastic response (present loading)Elastic response (present loading)East Ant. rheol.

West Ant. rheol.Jmax=2048Jmax= 90 & 200 km GaussianPage Nr.ESA CliC workshop, Troms, 20 January 2015Viscoelastic response should plot along orange line (and depend on the Earth model assumptions)Elastic on green line (only one set of elastic Earth parameters: PREM)Advantage: each dataset can be considered in the adequate resolution27GRACE e vs. GPS u (Altim. removed)

East Ant. rheol.

West Ant. rheol.Page Nr.ESA CliC workshop, Troms, 20 January 2015This is how the GPS data plot (red circles without error bars >10 mm/yr, estimated manually)Some structure visible. But data reveals mixed signals (remaining elastic, i.e. presnet-day ice-mass change and GIA).Estimation using system of equations shown earlier.28Elastic and viscoelastic kernels

Axisymmetric disc load: 62 km radius, mass gain 5.6 Gt/yr Temporal evolutionJmax=2048~ 10 kmRadius constantLoad rate constant Viscoelastic Earth model: Martinec, 2000V. Klemann, I. Sasgen, GFZPage Nr.ESA CliC workshop, Troms, 20 January 2015Viscoelastic response function computed for disc load experiment run to steady state. Disc radius 62 km (geodesic grid) at mass rate of 5.6 Gt/yr. Earth model varied to account for special conditions in West Antarctica.

REMOVE.29Sheet1Ocean sectorIce shelvesGLF SMBCFdh/dtBMBAreaSBMBMRGtyr-1Gtyr-1Gtyr-1Gtyr-1Gtyr-1103 km2myr-1%West Indian OceanAR, NE, AIS, W*2353049815522-118-14038174-0.800.2247West Indian Ocean+32431-20429--17943--47East Indian OceanSHA*, VAN, TOT*, MU, POR*, 3331648721344-5120-2194865-3.350.7351East Indian Ocean+ADE*, MER, NIN*, COO, REN*50826-30675--30080--50Ross SeaDRY, RIS, SUL1491671171531000-6726492-0.140.0530Ross Sea+17516-16715--7928--32Amundsen SeaLAN*, GET*, CD*, THW*, PI*, COS*38319551119843-15613-3954856-7.110.8767Amundsen Sea+50524-23250--48457--68Bellingshausen SeaABB*, VEN*, GEO*, WOR1391182163110-6543-2552286-2.980.2689Bellingshausen Sea+17412-4113--28123--87Weddell SeaLBC, FRIS, BRL, JFL33435139233553100-11852608-0.190.0925Weddell Sea+36335-37133--13153--26Fringing West Antarctica SUL, LAN, GET, CD, THW, PI, 542231471923254-22145-67853154-4.400.3574Fringing West Antarctica+COS, ABB, VEN, GEO, WOR70027-27563--79262--74Total Surveyed 1,57356444361,106141-28250-1,1931631,481-0.810.1152Total Upscaling 47667-21633--2613474-3.530.4755Total Antarctica2,04987-1,321144--1,4541741,555-0.940.1152

Sheet2

Sheet3