Discussion about the role of geodesy in glacial isostatic adjustment (GIA) research by showing examples where GIA models are needed and what uncertainties we have in GIA models

Steffen, Rebekka

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GLACIAL ISOSTATIC ADJUSTMENT AND ITS ROLE IN GEODESYREBEKKA STEFFENGGOS DAYS 2023NKG – NORDIC GEODETIC COMMISSIONCooperation by researchers in geodesy within the Nordic countriesnational mapping authorities, universities and research institutesmost work is done within the working groups• WG of Reference Frames• WG of Height and Geoid• WG of Geodynamics and Earth Observation• WG of GNSS Positioningaddresses topics that are of common Nordic interest (e.g., glacial isostatic adjustment)2Whitehouse (2018)GLACIAL ISOSTATIC ADJUSTMENT (GIA)34WHY IS GIA OF INTEREST FOR GEODESY?GIA – OBSERVATIONSHelpful constraintsToday’s accurate snapshotThe reliable past The blurry futureA model that can describe all that (and more) will provide us the view into the future!Relative sea level (paleo)3D land motion Gravity changesSeismicity, relative sea level (geodetic), Earth rotation parameters56WHY DO WE NEED A GIA MODEL IN GEODESY?GIA      signal vs. noiseAtmosphereOceanHydrosphereIce sheetsSolid Earth (without GIA)GRACE trend GIA model output DifferenceFigure courtesy: Andreas Kvas (Uni Graz)GIA      additional constraintsHäkli et al. (2023)WHY DO WE NEED A GIA MODEL IN GEODESY?7APPLICATION OF GIA MODELS IN GEODESYExample for northern Europe – NKG2016LU (Vestøl et al., 2019)Empirical model based on observations Best-fitting GIA model (based on GNSS and RSL data)8APPLICATION OF GIA MODELS IN GEODESYExample for northern Europe – NKG2016LU (Vestøl et al., 2019)Empirical model based on observations Final land uplift model9APPLICATION OF GIA MODELS IN GEODESYExample for northern Europe – NKG_RF17_vel (Häkli et al., 2019) Interpolation and extrapolation via least-squares collocation Requires input parameters Covariance analysis10APPLICATION OF GIA MODELS IN GEODESYExample for northern Europe – NKG_RF17_vel (Häkli et al., 2019) Covariance analysis without reducing a GIA model and doing a separateanalysis for each horizontal GNSS componentEW component NS component11APPLICATION OF GIA MODELS IN GEODESYExample for northern Europe – NKG_RF17_vel (Häkli et al., 2019) Covariance analysis without reducing a GIA model and doing a combined analysis of both horizontal GNSS components12APPLICATION OF GIA MODELS IN GEODESYExample for northern Europe – NKG_RF17_vel (Häkli et al., 2019) Covariance analysis with reducing a GIA model and doing a combinedanalysis of both horizontal GNSS components13APPLICATION OF GIA MODELS IN GEODESYExample for northern Europe – NKG_RF17_vel (Häkli et al., 2019) Covariance analysis with reducing a GIA model and doing a combinedanalysis of both horizontal GNSS componentsWithout reducing the GIA model Reducing the GIA model14GIA – MODELLINGWhitehouse (2018)GIA observables:Geodetic (3D land motion, gravitychanges, earth rotation changes, relative sea level and ice extent)Paleo (relative sea level, lake leves, ice extent, seismicity)Earth parameters:Mantle viscosityLithospheric thicknessRheological parameters (Poisson’s ratio, Young’smodulus, density)Rheological model15GIA – MODELLINGUncertainties in GIA modellingWhitehouse (2018)Nield et al. (2018)Steffen & Steffen (in prep.)16GIA –VERTICALVELOCITIESIce model: ICE-6GEarth model: VM5aGIA code: ICEAGESteffen & Steffen (in prep.) 17GIA –VERTICALVELOCITIES18Ice model: ICE-6GEarth model: VM5aGIA code: ICEAGESteffen & Steffen (in prep.)GIA –VERTICALVELOCITIES19Ice model: ICE-6GEarth model: VM5aGIA code: ICEAGEIce model: ICE-6GEarth model: 90 km, 4 ⋅ 1019 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠, 2 ⋅ 1021 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠GIA code: ICEAGESteffen & Steffen (in prep.)GIA – HORIZONTALVELOCITIES20Ice model: ICE-6GEarth model: VM5aGIA code: ICEAGESteffen & Steffen (in prep.)GIA – HORIZONTALVELOCITIES21Ice model: ICE-6GEarth model: VM5aGIA code: ICEAGESteffen & Steffen (in prep.)GIA – HORIZONTALVELOCITIES22Ice model: ICE-6GEarth model: VM5aGIA code: ICEAGEIce model: ICE-6GEarth model: 90 km, 4 ⋅ 1019 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠, 2 ⋅ 1021 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠GIA code: ICEAGESteffen & Steffen (in prep.)GIA – MODEL CHOICE23Lithospheric thickness: 80 kmUpper mantle viscosity: 4 ⋅ 1020 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠Lower mantle viscosity: 2 ⋅ 1021 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠Lithospheric thickness: 60 kmUpper mantle viscosity: 4 ⋅ 1020 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠Lower mantle viscosity: 4 ⋅ 1021 𝑃𝑃𝑃𝑃 ⋅ 𝑠𝑠Best fit 𝜒𝜒 to vertical GNSS data based on Khan et al., 2016Compressible IncompressibleGIA – MODEL CHOICE24Compressible best-fit model Incompressible best-fit modelGLACIAL ISOSTATIC ADJUSTMENT (GIA) – OBSERVATIONSHelpful constraintsToday’s accurate snapshotThe reliable past The blurry futureA model that can describe all that (and more) will provide us the view into the future!Relative sea level (paleo)3D land motion Gravity changesSeismicity, relative sea level (geodetic), Earth rotation parameters25GIA models are needed in various geoscientific fields, especially in geodesyRequires the availability of openly accessible model results, including uncertainty and details about the input parameters

Glacial isostatic adjustment and its role in geodesy

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Glacial isostatic adjustment and its role in geodesy

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