G3.3 | Advances in investigations of glacial isostatic adjustment and its role in the Earth system
Advances in investigations of glacial isostatic adjustment and its role in the Earth system
Co-organized by CL5/CR7/GD10/GM6/NP8, co-sponsored by SCAR
Convener: Holly Han | Co-conveners: Holger Steffen, Meike Bagge, Tanghua Li, Jun'ichi Okuno
| Thu, 27 Apr, 14:00–15:45 (CEST)
Room -2.47/48
Posters on site
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
Hall X2
Posters virtual
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
Orals |
Thu, 14:00
Thu, 16:15
Thu, 16:15
Glacial Isostatic Adjustment (GIA) describes the dynamic response of the solid Earth to the waxing and waning of ice sheets and corresponding spatial and temporal sea-level changes, which causes surface deformation and changes in the gravity field, rotation, and stress state of the Earth. The process of GIA is mainly influenced by the ice-sheet evolution and solid Earth structure, and in turn influences other components of the Earth system such as the cryosphere (e.g., ice sheets) and hydrosphere (e.g., ocean and sea level). A large set of observational data (e.g., relative sea level, GNSS measurements, tide gauges, terrestrial and satellite gravimetry, satellite altimetry, glacially induced faults) that can be used to constrain highly sophisticated GIA models is available nowadays in standardized form, which will further help in investigating the ice-sheet and sea-level evolution histories and rheological properties of the Earth, and understanding the interactions between ice sheets, the solid Earth and sea levels.

This session invites contributions discussing observations, analysis, and modelling of GIA and its effects on the Earth system across a range of spatial and timescales. Examples include, but not limited to, geodetic measurements of crustal motion and gravitational change, GIA modelling with complex Earth models (e.g., 3D lithosphere and/or viscosity, non-linear rheologies), GIA-induced global, regional and local sea-level changes, coupled GIA-ice sheet modelling for investigating past and future ice sheets/shelves changes and associated sea-level changes, glacially triggered faulting as well as the Earth’s (visco-)elastic response to present-day ice-mass changes. We also welcome abstracts that address GIA effects on nuclear waste repositories, groundwater distribution and migration of carbon resources. This session is co-sponsored by the SCAR sub-committee INSTANT-EIS, Earth - Ice - Sea level, in view of instabilities and thresholds in Antarctica https://www.scar.org/science/instant/home/ and PALMOD, the German Climate Modeling Initiative https://www.palmod.de.

Orals: Thu, 27 Apr | Room -2.47/48

Chairpersons: Holly Han, Meike Bagge, Tanghua Li
Virtual presentation
Stephanie Konfal, Terry Wilson, Pippa Whitehouse, Grace Nield, Tim Hermans, Wouter van der Wal, Michael Bevis, Demián Gómez, and Eric Kendrick

ANET-POLENET (Antarctic Network of the Polar Earth Observing Network) bedrock GNSS sites in the Ross Sea region of Antarctica surround an LGM load center in the Siple region of the Ross Embayment and record crustal motion due to GIA.  Rather than a radial pattern of horizontal motion away from the former load, we instead observe three primary patterns of deformation; 1) motions are reversed towards the load in the southern region of the Transantarctic Mountains (TAM), 2) motions are radially away from the load in the Marie Byrd Land (MBL) region, and 3) an overall gradient in motion is present, with magnitudes progressively increasing from East to West Antarctica.  We investigate the effects of alternative Earth model and ice loading scenarios, with the goal of understanding these distinct patterns of horizontal bedrock motion and their drivers. Using GIA models with a range of 1D Earth models, alternative ice loading scenarios for the Wilkes Subglacial Basin (LGM time scale) and the Siple Coast (centennial and millennial time scales) are explored.  We find that no 1D model, regardless of the Earth model and ice loading scenario used, reproduces all three distinct patterns of observed motion at the same time.  For select ice loading scenarios we also examine the influence of more complex rheology by invoking a boundary in Earth properties beneath the Transantarctic Mountains.  This approach accounts for the strong lateral gradient in Earth properties across the continent by effectively separating East and West Antarctica into two different Earth model profiles.  Some of our GIA models utilizing 3D Earth structure reproduce predicted motions that match all three observed patterns of deformation, and we find that a multiple order magnitude of change in upper mantle viscosity between East and West Antarctica is required to fit the observations. 

How to cite: Konfal, S., Wilson, T., Whitehouse, P., Nield, G., Hermans, T., van der Wal, W., Bevis, M., Gómez, D., and Kendrick, E.: Observations and modelling of GIA in the Ross Sea region, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10729, https://doi.org/10.5194/egusphere-egu23-10729, 2023.

On-site presentation
Florence Ramirez, Kate Selway, Clinton Conrad, Maxim Smirnov, and Valerie Maupin

Fennoscandia is continuously uplifting in response to past deglaciation, a process known as glacial isostatic adjustment or GIA. One of the factors that controls the uplift rates is the viscosity of the upper mantle, which is difficult to constrain. Here, we reconstruct the upper mantle viscosity structure of Fennoscandia by inferring temperature and water content from seismic and magnetotelluric (MT) data. Using a 1-D MT model for Fennoscandian cratons together with a global seismic model, we infer an upper mantle viscosity range of ~1019 - 1024 Pa·s for 1 – 10 mm grain size, which encompasses the GIA-constrained viscosities of 1020 - 1021 Pa·s. The associated viscosity uncertainties of our calculation are attributed to the uncertainties associated with the geophysical data and unknown grain size. We can obtain tighter constraints if we assume that the Fennoscandian upper mantle is either a wet harzburgite (1019.2 - 1023.5 Pa·s) or a dry pyrolite (1020.0 - 1023.6 Pa·s) below 250 km, where pyrolite is ~10 times more viscous than harzburgite. Furthermore, assuming a constant grain size of either 1 mm or 10 mm reduces the viscosity range by approximately 2 orders of magnitude. In northwestern Fennoscandia, where a high-resolution 2-D resistivity model is available, the calculated viscosities are ~10 - 100  times lower than those for the Fennoscandian craton because the mantle has a higher water content, and both pyrolite and harzburgite must be wet. Overall, our calculated viscosities for Fennoscandia that are constrained from seismic and MT observations agree with the mantle viscosities constrained from GIA. This suggests that geophysical observations can usefully constrain upper mantle viscosity, and its lateral variations, for other parts of the world without GIA constraints.

How to cite: Ramirez, F., Selway, K., Conrad, C., Smirnov, M., and Maupin, V.: Lateral and radial viscosity variations beneath Fennoscandia inferred from seismic and MT observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15597, https://doi.org/10.5194/egusphere-egu23-15597, 2023.

Virtual presentation
Sophie Coulson, Matthew Hoffman, Kelian Dascher-Cousineau, Brent Delbridge, Roland Bürgmann, and Joshua Carmichael

Ice mass loss from the Greenland Ice Sheet and Arctic glaciers has accelerated over the last three decades due to rapid changes in Arctic climate. This loss of ice from glaciated areas and redistribution of water across the global oceans creates a complex spatio-temporal pattern of crustal deformation due to the load changes on Earth’s surface. We test whether the resulting strain perturbations from this deformation are large enough to influence seismic activity in the Arctic on decade to century timescales.


Using new ice-mass-loss estimates from radar altimetry for the Greenland Ice Sheet and model reconstructions of glaciers across the European Arctic, we predict gravitationally self-consistent sea level changes across the Arctic over the last three decades. These surface loads are then used as input for our deformation model, developed to calculate strain at depth within the crust, using a Love number formulation for a spherically symmetric Earth. Our global model captures both the near-field effects directly beneath ice centers and deformation across the sea floor, allowing us to fully quantify the spatio-temporal perturbations to the regional strain field created by glacial isostatic adjustment (GIA) processes. Using declustered earthquake catalogs of Arctic earthquake activity over the last three decades, we search for correlation between the earthquake record and our modelled strain perturbations. In particular, we focus our search along the Mid Atlantic Ridge and beneath Greenland. In the former, small magnitude GIA-related strains enhance or counteract rapid tectonic background loading, while in the latter intra-plate setting, GIA processes likely dominate the crustal strain field.


While correlations over the last three decades may not be statistically definitive, this framework also allows for prediction of crustal strain patterns for future ice sheet scenarios, as ice mass loss from Greenland accelerates, and therefore predictions of the likelihood and potential geographic variability of climate-change-induced seismicity in the future.

How to cite: Coulson, S., Hoffman, M., Dascher-Cousineau, K., Delbridge, B., Bürgmann, R., and Carmichael, J.: Quantifying the Impact of Modern Ice Mass Loss on Crustal Strain and Seismicity across Greenland and the European Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9405, https://doi.org/10.5194/egusphere-egu23-9405, 2023.

On-site presentation
Lev Tarasov, Benoit Lecavalier, Greg Balco, Claus-Dieter Hillenbrand, Glenn Milne, Dave Roberts, and Sarah Woodroffe

We present the Antarctic and Greenland components of an extensive
history matching for last glacial cycle evolution and regional earth
rheology from glaciological modelling with fully coupled regional
visco-elastic glacio-isostatic adjustment.  Of further distinction is
the accounting for model structural uncertainty. The product is a high
variance set of joint chronologies and earth model parameter vectors
that are not inconsistent with available constraints given
observational and model uncertainties.

Ensemble parameters are from Markov Chain Monte Carlo sampling with
Bayesian artificial neural network emulators.  The glaciological model
is the Glacial Systems Model with hybrid shallow shelf and shallow ice
physics and a coupled energy balance climate model. It includes a much
larger set of ensemble parameters (34 and 38 respectively for
Greenland and Antarctica) than other paleo ice sheet models to
facilitate more complete assessment of past ice sheet evolution
uncertainty. The history matching is against a large curated set of
relative sealevel, vertical velocity, cosmogenic age, and marine
constraints as well as the present-day physical and thermal
configuration of the ice sheet.

The careful assessment of uncertainties, breadth of modelled
processes, and sampling approach has resulted in NROY (not ruled out
yet) chronologies and rheological inferences that contradict previous
more limited model-based reconstructions.  For instance, in contrast
to most previous inferences for the Antarctic contribution to the last
glacial maximum (LGM) low-stand (with inferred values of about 10 m ice
equivalent sea-level (mESL), our NROY set includes chronologies with
LGM contributions of up to 23 mESL.  This result represents a
potentially significant contribution towards addressing the challenge
of LGM missing ice.

How to cite: Tarasov, L., Lecavalier, B., Balco, G., Hillenbrand, C.-D., Milne, G., Roberts, D., and Woodroffe, S.: GLAC3: Joint glaciological model and visco-elastic earth model history matching of the last glacial cycle: Greenland and Antarctica components, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10574, https://doi.org/10.5194/egusphere-egu23-10574, 2023.

Virtual presentation
Terry Wilson, Demián Gómez, Peter Matheny, Michael Bevis, William J. Durkin, Eric Kendrick, Stephanie Konfal, and David Saddler

Twelve continuous GNSS systems are deployed on bedrock across the Amundsen Embayment region, spanning the Pine Island, Thwaites and Pope-Smith-Kohler (PSK) glacial drainage network of the West Antarctic Ice Sheet.  Continuous daily position time series for these sites range from 4 to 12 years, yielding reliable crustal motion velocity solutions at these fast-moving bedrock sites. Remarkably, multiple stations record sustained uplift of 40-50 mm/yr.  Maximum uplift defined by the current distribution of sites is centered on the Pope-Smith-Kohler glaciers, where rapid thinning and grounding line retreat is well documented. Horizontal bedrock displacements, which are particularly sensitive to the location of changing surface mass loads, show a clear radial pattern with motion outward away from upstream portions of the Pope/Smith glaciers. Several modeling studies suggest there is a viscous deformation response to this decadal mass loss. Our modeling, however, shows that elastic deformation response explains nearly the entire measured signal at the PSK region sites. We will present new modeling results and discuss implications for ongoing cryosphere-solid Earth interactions.

How to cite: Wilson, T., Gómez, D., Matheny, P., Bevis, M., Durkin, W. J., Kendrick, E., Konfal, S., and Saddler, D.: New GNSS Observations of Crustal Deformation due to Ice Mass Loss in the Amundsen Sea Region, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10493, https://doi.org/10.5194/egusphere-egu23-10493, 2023.

On-site presentation
Evelyn Powell and James Davis

The GRACE (Gravity Recovery and Climate Experiment) satellites measure the Earth’s geopotential, and we can use this data to monitor spatiotemporal mass load changes in Earth's ice sheets. The geopotential measurements are both resolution-limited by the orbital configurations and subject to the complexities of present-day sea level change; for example, when an ice sheet melts, the accompanying migration of water should lead to a systematic bias in GRACE estimates of ice mass loss (Sterenborg et al., 2013). Indeed, using mascons and an iterative approach, Sutterley et al. (2020) found that variations in regional sea level affect ice sheet mass balance estimates in Greenland and in Antarctica by approximately 5%. Here, we use the sea level equation in our inferences of ice-mass loss both to increase the resolution of those inferences and to include the sea-level response in the analysis of GRACE data. We will test the resolution, implementation, accuracy, and impacts of a constrained least squares inversion of GRACE data. We will then investigate how deformation associated with our estimates of ongoing global surface mass change affects Earth-model inferences from geodetic data and Glacial Isostatic Adjustment modeling, with a focus region of Fennoscandia.

How to cite: Powell, E. and Davis, J.: Using the sea level equation to increase the resolution of GRACE inferences: Implications for studies of Fennoscandian GIA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17418, https://doi.org/10.5194/egusphere-egu23-17418, 2023.

On-site presentation
Kaixuan Kang and Shijie Zhong

In this study, we examine the relationships among mantle viscosity, ice models and RSL data. We analyzed two widely used ice models, the ANU and ICE-6G ice models, and found significant difference between these two models, suggesting that significant uncertainties exist in ice models. For six RSL datasets covered both the near- and far-field from published works [Peltier et al., 2015; Lambeck et al., 2014, 2017; Vacchi et al., 2018; Engelhart et al., 2012, 2015], we performed forward GIA modelling using a 1-D compressible Earth model to seek the preferred upper and lower mantle viscosities that fit each of the six RSL datasets, for each of these two ice models. Our calculations show that viscosity in the lower mantle is significantly larger than the upper mantle for almost all the pairs of RSL datasets and ice models, but the RSL datasets for North America and Fennoscandia by Peltier et al., [2015] can be matched similarly well with a large parameter space of upper and lower mantle viscosities, both relatively uniform mantle viscosity and with large increase with depth. The preferred mantle viscosity using the ANU ice model and Lambeck et al. [2017] RSL data for North America is in a good agreement with that by Lambeck et al. [2017].    By using the GIA model with the preferred viscosity structures, we constructed the spatial and temporal distributions of misfit to different RSL datasets, for both the ICE-6G and ANU ice models. The misfit patterns for the ANU and ICE-6G ice models do not differ significantly in North America, although these two ice models differ greatly in North America. However, due to relatively small ice volume in ICE-6G, it fails to explain the far-field RSL data, reflecting the so-called “missing ice” problem. Guided by the spatial and temporal misfit patterns, we made initial attempts to modify ICE-6G by adding more ice to the ice model to improve the fit to far-field RSL data. The three modified ICE-6G ice models we consider all significantly improve far-field RSL data, while maintaining or even improving misfit for near field RSL data. This shows the promise with our method in improving ice models and fit to RSL data.

How to cite: Kang, K. and Zhong, S.: Constraints of Relative Sea Level Change on the Late Pleistocene Deglaciation History, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9697, https://doi.org/10.5194/egusphere-egu23-9697, 2023.

Virtual presentation
Jan Swierczek-Jereczek, Marisa Montoya, Javier Blasco, Jorge Alvarez-Solas, and Alexander Robinson

Glacial isostatic adjustment (GIA) represents an important negative feedback on ice-sheet dynamics. The magnitude and time scale of GIA primarily depend on the upper mantle viscosity and the lithosphere thickness. These parameters have been found to vary strongly over the Antarctic continent, showing ranges of 1018 - 1023 Pa s for the viscosity and 30 - 250 km for the lithospheric thickness. Recent studies show that coupling ice-sheet models to 3D GIA models capturing these spatial dependencies results in substantial differences in the evolution of the Antarctic Ice Sheet compared to the use of 1D GIA models, where the solid-Earth parameters are assumed to depend on the latitude but not on the longitude and the depth. However, 3D GIA models are computationally expensive and sometimes require an iterative coupling for the ice sheet and the solid-Earth solutions to converge. As a consequence, their use remains limited, potentially leading to errors in the simulated ice-sheet response and associated sea-level rise projections. Here, we propose to tackle this problem by generalising the Fourier collocation method for solving GIA proposed by Lingle and Clark (1985) and implemented by Bueler et al. (2007). The method allows for an explicit accounting of the effects of spatially heterogeneous viscosity and lithospheric thicknesses and is computationally very efficient. Thus, for a continental domain at relatively high spatial resolution (256 x 256 grid points) and a 1-year time step, the model runs with speeds of ca. 200 simulation years per second on a single CPU, while keeping the error low compared to 3D GIA models. As the time step is small enough, the need of an iterative coupling method is avoided, thus making the model easy to couple with ice-sheet models.

How to cite: Swierczek-Jereczek, J., Montoya, M., Blasco, J., Alvarez-Solas, J., and Robinson, A.: A generalised Fourier collocation for fast computation of glacial isostatic adjustment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13583, https://doi.org/10.5194/egusphere-egu23-13583, 2023.

On-site presentation
Ryan Love, Parviz Ajourlou, Soran Parang, Glenn A. Milne, Lev Tarasov, and Konstantin Latychev

At present, exploring the space of rheological parameters in models of glacial isostatic adjustment (GIA) and relative sea level (RSL) which incorporate laterally variable Earth structure is computationally expensive. A single simulation using the Seakon model (Latychev et al., 2005), using contemporary high-performance computing hardware, requires several wall-days & ≈ 1 core-year for one RSL simulation from late Marine Isotope Stage 3 to present day. However, it is well established that the impact from laterally variable mantle viscosity and lithospheric thickness on RSL and GIA is significant (Whitehouse, 2018). We present initial results from using the Tensorflow (Abadi et al.) framework to construct artificial neural networks that emulate the difference in the rate of change of relative sea level and relative radial displacement between model configurations using spherically symmetric (SS) and laterally variable (LV) Earth structures. Using this emulator we can accurately sample the parameter space (≈ 360 realisations of the background (SS) structure) for a given realization of lateral Earth structure (e.g. viscosity variations derived from shear-wave tomographic models) using ≈ 1/10th the amount of parameter vectors as a training set. Average misfits are O(0.1-1%) of the total RSL signal when using the emulator to adjust SS GIA model output to incorporate the impact from LV. We shall report on two case studies which allow us to examine the influence of lateral Earth structure on inferences of background (i.e. global-mean) viscosity. For these case studies, the emulator, in conjunction with a fast SS GIA/RSL model, is used to determine optimal Earth model parameters (elastic lithosphere thickness, upper and lower mantle viscosities) by calculating the model misfits across the parameter space. The first case study uses the regional RSL database of Vacchi et al. (2018) which spans the Canadian Arctic and East Coast with several hundred sea level index points and limiting points for the early to late Holocene. The second case study uses a global database of several thousand contemporary uplift rates derived from GPS data (Schumacher et al., 2018). For the first case study we find two main features from incorporating LV structures compared to the SS configuration: a decrease in the best scoring misfit and a shift of the misfit distribution in the parameter space to favour a reduced upper mantle viscosity and reduced sensitivity to the lower mantle viscosity.

Abadi, M., Agarwal, A., Barham, P., et al.: TensorFlow: Large-Scale Machine Learning on Heterogeneous Systems, https://www.tensorflow. org/.
Latychev, K., Mitrovica, J. X., Tromp, J., et al.: Glacial isostatic adjustment on 3-D Earth models: a finite-volume formulation, GJI, 161, 421–444, https://doi.org/10.1111/j.1365-246x.2005.02536.x, 2005.
Schumacher, M., King, M. A., Rougier, J., et al.: A new global GPS data set for testing and improving modelled GIA uplift rates, GJI, 214, 2164–2176, https://doi.org/10.1093/gji/ggy235, 2018.
Vacchi, M., Engelhart, S. E., Nikitina, D., et al.: Postglacial relative sea-level histories along the eastern Canadian coastline, QSR, 201, 124–146, https://doi.org/10.1016/j.quascirev.2018.09.043, 2018.
Whitehouse, P. L.: Glacial isostatic adjustment modelling: historical perspectives, recent advances, and future directions, Earth Surface Dynamics, 6, 401–429, https://doi.org/10.5194/esurf-6-401-2018, 2018.

How to cite: Love, R., Ajourlou, P., Parang, S., Milne, G. A., Tarasov, L., and Latychev, K.: Emulating the influence of laterally variable Earth structure in a model of glacial isostatic adjustment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7921, https://doi.org/10.5194/egusphere-egu23-7921, 2023.


Posters on site: Thu, 27 Apr, 16:15–18:00 | Hall X2

Chairperson: Holger Steffen
alexandre boughanemi and anthony mémin

The Antarctic Ice Sheet (AIS) is the largest ice sheet on Earth that has known important mass changes during the last 26 kyrs. These changes deform the Earth and modify its gravity field, a process known as Glacial Isostatic Adjustment (GIA). GIA is directly influenced by the mechanical properties and internal structure of the Earth and is monitored using Global Navigation Satellite System positioning or gravity measurements. However, GIA in Antarctica remains poorly constrained due to the cumulative effect of past and present ice-mass changes, the unknown history of the past ice-mass change, and the uncertainties of the mechanical properties of the Earth. The viscous deformation due to GIA is usually modeled using a Maxwell rheology. However, other geophysical processes employ the Andrade rheology for tidal deformation or Burgers for post-seismic deformation which could result in a more rapid response of the Earth. We investigate the effect of using these different rheologies to model GIA-induced deformation in Antarctica.
We use the Love number and Green functions formalism to compute the radial surface displacements and the gravity changes induced by the past and present day ice-mass changes. We use the elastic properties and the radial structure of the Preliminary Reference Earth Model (PREM) and the viscosity profile VM5a given by Peltier et al., 2015 and a modified version of it to account for the recent results published regarding the present-day ice-mass changes. Deformations are computed for each rheological laws mentioned above using ICE6g deglaciation model and altimetry data from various satellite missions over the period 2002 to 2017 to represent the past and present changes of the AIS, respectively.
We find that the three rheological laws lead to significant discrepancies in the Earth response. The differences are the largest between Maxwell and Burgers rheologies during the 100 -1000 years following the beginning of the surface-mass change. First using a simple deglaciation model, we find that the deformations rates can be 3 times and 1.5 times greater using the Burgers and Andrade rheologies. However, the ratio between the gravity change rate and the displacement rate are similar for all rheologies (less than 5% difference). Results show that using the Andrade and Burgers rheologies can lead to a 5 and 10m difference in the radial displacement with regards to the Maxwell rheology, on a 200 year period after deglaciation using the ICE6g model. Regarding the response to present changes in Antarctica, the largest discrepancies are obtained in regions with the greatest current melting rates, namely Thwaites and Pine Island Glacier in West Antarctica. Using the Burgers and Andrade rheologies lead to deformations rates respectively 6 times and 2 times greater with respect to Maxwell rheology.

How to cite: boughanemi, A. and mémin, A.: Study of the impact of rheologies on GIA modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6911, https://doi.org/10.5194/egusphere-egu23-6911, 2023.

Meike Bagge, Eva Boergens, Kyriakos Balidakis, Volker Klemann, and Henryk Dobslaw

Models of glacial isostatic adjustment (GIA) simulate the time-delayed viscoelastic response of the solid Earth to surface loading induced mainly by mass redistribution between ice and ocean during the last glacial cycle considering for rotational feedback, floating ice and moving coastlines. These models predict relative sea level change and surface deformation. The GIA component of present-day uplift is responsible for crustal uplift rates of more than 10 mm/year in areas such as Churchill (Canada) and Angermanland (Sweden). As GIA models have several uncertainties, the model output needs to be validated against observational data. Here, we validate displacements predicted by a GIA model code, VILMA-3D, by using space geodetically observed vertical land motion. We have created a GIA model ensemble using geodynamically constrained 3D Earth structures derived from seismic tomography to consider more realistic lateral variations in the GIA response. To validate the modelled uplift rates, we employ a multi-analysis-centre ensemble of GNSS station and geocentre motion coordinate solutions that have been assimilated into the latest international terrestrial reference frame (ITRF2020). Tectonic and weather signatures were reduced in estimating GNSS-derived velocities, and the trend signal is extracted from these GNSS time series with the STL method (seasonal-trend decomposition based on Loess).  Additionally, uplift rates observed within the ITRF2020 of VLBI, DORIS, and SLR are employed in this study. Because the geodetic stations are unevenly distributed, we employ a weighting scheme that involves the network density and the cross-correlation of the stations’ displacement time series. As measures of agreement for global and regional cases, we employ weighted root mean square error (RMSE) and weighted mean absolute error (MAE). With this validation, we determine the GIA model parameters that are most suitable for modelling present-day uplift rates and identify regions with the best and worst agreement.

The results show an agreement between RMSE and MAE for the global case (all stations are considered) and the majority of regional cases, except for the farfield (away from formerly glaciated regions) and for North America. For the global case and for separate regions covered by the major ice sheets during glaciation (North America, Fennoscandia, Antarctica, Greenland), the best fit is performed by the GIA models with 3D Earth structures which show largest lateral variability in viscosity. For the GIA model with the best global fit, the MAE ranges between 0.03 and 0.98 for the respective regions British Isles, Antarctica, farfield, Fennoscandia and North America. In contrast, for the three regions with the lowest amount of observational data, Patagonia, Alaska and Greenland, the MAE is increased to values between 2.07 and 8.63. In general, the MAE ranges between 0.83 and 0.78 for the different GIA models when all stations are considered. Both the RMSE and the MAE show a larger spread between the regions than between the considered GIA models indicating the relevance of also evaluating regional differences in the model performance.

How to cite: Bagge, M., Boergens, E., Balidakis, K., Klemann, V., and Dobslaw, H.: Validation of Modelled Uplift Rates with Space Geodetic Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3351, https://doi.org/10.5194/egusphere-egu23-3351, 2023.

Aleksey Amantov, Marina Amantova, Lawrence Cathles, and Willy Fjeldskaar

The existence and nature of Quaternary glaciations of the eastern part of the Arctic basin is very far from being solved, and many think glaciations there may been absent or very local, even at the Last Glacial Maximum.  It is unlikely under the conditions of permafrost and low precipitation during MIS 2, that the glaciers would have produced significant topographic relief.  However, significant ice loads will produce a significant isostatic response.  In the area of the Novosibirsk Islands, Holocene changes in sea level and transitions from continental to marine sedimentation indicate differences in emergence over the course of the transgression  that suggest the melting of significant grounded ice masses (e.g. Anisimov et al., 2009). Shorelines deviate from those expected from the hydroisostatic component. The best-fit isostatic model suggests significant LGM ice accumulation close to the ocean in the area of the Henrietta and Jeannette islands of the De Long archipelago in the East Siberian Sea. The uplift deviations in the Zhokhov island district are best matched for an effective elastic lithosphere thickness Te ~40 km. The ice accumulations close to the shelf-ocean margin in the last glaciation seem to also have occurred in earlier glaciations of the region.

Anisimov, M.A., Ivanova, V.V., Pushina, Z.V., Pitulko, V.V. 2009. Lagoon deposits of Zhokhov Island: age, conditions of formation and significance for paleogeographic reconstructions of the Novosibirsk Islands region // Izvestiya RAS, Geographical Series. No. 5. pp. 107-119.

How to cite: Amantov, A., Amantova, M., Cathles, L., and Fjeldskaar, W.: Glaciations of the East Siberian Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17095, https://doi.org/10.5194/egusphere-egu23-17095, 2023.

Posters virtual: Thu, 27 Apr, 16:15–18:00 | vHall GMPV/G/GD/SM

Chairpersons: Holly Han, Jun'ichi Okuno
Tanghua Li, Ane García-Artola, Jennifer Walker, Alejandro Cearreta, and Benjamin Horton

Vertical land motion (VLM) is an important component in relative sea-level (RSL) projections, especially at regional to local scales and over the short to medium term. However, VLM is difficult to derive because of a lack of long-term instrumental records (e.g., GPS, tide gauge). Geological data offer an alternative, revealing RSL histories over thousands of years that can be compared with glacial isostatic adjustment (GIA) models to isolate VLM.

Here, we present a case study from the Oka estuary, northern Spain. We apply two GIA models for the Atlantic coast of Europe with different ice model inputs (ICE-6G_C and ANU-ICE) but the same 3D Earth model. Both models fit well with the late Holocene RSL data along the Atlantic coast of Europe, with misfit statistics < 1.5, except the Oka estuary region, where both models show notable misfits with misfit statistics > 4.5. The significant misfits of both models in the Oka estuary region are indicative of local subsidence. The nearby GPS (station SOPU) with 15 years records shows a VLM rate of -0.96 ± 0.57 mm/yr (subsiding) compared to -0.15 ± 0.40 mm/yr to -2.48 ± 0.37 mm/yr elsewhere along the Atlantic coast of Europe. The VLM rate of SOPU accounts for the misfit between the GIA models and late Holocene RSL data, which decreases by ~90% from > 4.5 to ~0.5 after the subsidence correction of the late Holocene RSL data. The VLM rate incorporated in IPCC AR6 projections in Oka estuary is ~0.18 mm/yr (uplifting), which is contradictory in direction. Therefore, the projected sea-level rise rate is underestimated by 19 - 25% by 2030, 14 - 20% by 2050 and 9 - 26% by 2100 under the five Shared Socioeconomic Pathway (SSP) scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5). Our study indicates the importance of considering local/regional VLM component in sea-level projections.

How to cite: Li, T., García-Artola, A., Walker, J., Cearreta, A., and Horton, B.: The importance of underestimated local vertical land motion component in sea-level projections: A case study from the Oka estuary, northern Spain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4604, https://doi.org/10.5194/egusphere-egu23-4604, 2023.

Yoshiya Irie and Jun'ichi Okuno

Changes in Antarctic ice mass have been observed as gravity changes by the Gravity Recovery and Climate Experiment (GRACE) satellites. The gravity signal includes both the component of the ice mass change and the component of the solid Earth response to surface mass change (Glacial Isostatic Adjustment, GIA). Therefore, estimates of the ice mass change from GRACE data require subtraction of the gravity rates predicted by the GIA model (GIA correction).

Antarctica is characterized by lateral heterogeneity in seismic velocity structure. West Antarctica shows relatively low seismic velocities, suggesting low viscosity regions in the upper mantle. On the other hand, East Antarctica shows relatively high seismic velocities, suggesting a thick lithosphere. Here we investigate the dependence of the GIA correction on lithospheric thickness and upper mantle viscosity.

The GIA correction for the average viscoelastic structure of West Antarctica is nearly identical to that for the average viscoelastic structure of East Antarctica. There is a trade-off between the lithospheric thickness and the upper mantle viscosity. This trade-off may reduce the effect of the lateral variations in the Earth’s viscoelastic structure beneath Antarctica on estimates of Antarctic ice mass change.

How to cite: Irie, Y. and Okuno, J.: Sensitivity of Antarctic GIA correction for GRACE data to viscoelastic Earth structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17255, https://doi.org/10.5194/egusphere-egu23-17255, 2023.

Valentina R. Barletta, Andrea Bordoni, and Shfaqat Abbas Khan

Recent studies have shown that in the area of the Kangerlussuaq glacier, a large GPS velocities residual after removing predicted purely elastic deformations caused by present-day ice loss suggests the possibility of a fast rebound to little ice age (LIA) deglaciation. We previously investigated this area with a Maxwell viscoelastic rheology Earth model and compared the model predictions with GPS residual. We found a match for a rather thick lithospheric thickness and a rather low mantle viscosity structure beneath SE-Greenland. In this study we are going to examine the effect of a Burger model: 1) we compare the results with those from the Maxwell model and 2) we estimate if and where the differences can be discriminated with observational data.
Maxwell models describe a steady state mantle deformation and they are the most commonly model used in post glacial rebound problems. Burgers models, instead, describe a time-varying mantle deformation, which include an initial fast transient components followed by a steady-state phase of mantle deformation. This kind of transient deformation would allow to reconcile the Earth rebound caused by the Pleistocene deglaciation and the faster rebound caused by the recent LIA deglaciation.
We then analyze several scenarios of ice retreat in the last 2000 years in the fiord in front of Kangerlussuaq glacier, in view of the difference between the two rheologies.

How to cite: Barletta, V. R., Bordoni, A., and Khan, S. A.: Effect of transient deformation in southeast Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14958, https://doi.org/10.5194/egusphere-egu23-14958, 2023.