Glacial isostatic adjustment
Glacial isostatic adjustment (GIA) describes how the Earth reacts to loading caused by ice sheets. The still ongoing adjustment of the Earth's body to the redistribution of ice and water masses during and after the last glacial period manifests itself in a series of phenomena. These are investigated in order to estimate the extent and thickness of the former ice masses, to reconstruct the sea level over a glacial cycle and to determine the rheological properties of the Earth, essentially its viscosity structure.
The glaciation phases during a glacial are characterized by a slow growth of the ice sheets followed by rapid melting. Each glacial phase lasted about 40,000 years. During the last 700,000 years, the phases were extended to about 100,000 years. They are interrupted by relatively short warm periods, the so-called interglacials or interglacial periods, which only last a few thousand years; we are currently in the last one. During the last glacial maximum around 21,000 years ago, the ice sheets of North America, Scandinavia and Antarctica stored so much water that the global sea level fell by around 120 meters. These ice loads, which were several kilometers thick, deformed the earth to such an extent that the ground in the frozen areas sank by several hundred meters. Between 21,000 and 8,000 years ago, the ice sheets melted and the global sea level reached approximately its current level. The solid earth, on the other hand, is still reacting with a delay: mantle material that was displaced during the glaciation is still flowing back. This causes the well-known uplift motion in northern Sweden and eastern Canada, which reach one centimeter per year.
... which are described as a shift in the equipotential surface of the gravitational field (the geoid). This isostatic imbalance results in a low geoid in the formerly glaciated areas. The adjustment process reduces the geoid depression through the inflow of mantle material. A prominent example can be found in northeastern Canada, where the geoid is lowered by about 40 m, showing that isostatic equilibrium has not yet been reached after the retreat of the Laurentian ice sheet. For this area, however, it must be noted that at least 50 percent is due to a density anomaly and thus to mantle convection (e.g. Mitrovica & Vermeersen, 2002, Ice Sheets, Sea Level and the Dynamic Earth. American Geophysical Union, Washington). Today's changes in the ice sheets, on the other hand, dominate the geoid due to their direct mass attraction, whereas the elastic response of the solid Earth is comparably small. In Antarctica or Greenland, the mass changes observed with GRACE are thus caused by recent melting as well as by GIA.
References:
Eicker, A., Schawohl, L., Middendorf, K., Bagge, M., Jensen, L., Dobslaw, H. (2024): Influence of GIA uncertainty on climate model evaluation with GRACE/GRACE-FO satellite gravimetry data. - Journal of Geophysical Research: Solid Earth, 129, 5, e2023JB027769.
doi.org/10.1029/2023JB027769
Dobslaw, H., Bergmann, I., Dill, R., Forootan, E., Klemann, V., Kusche, J., Sasgen, I. (2015): The updated ESA Earth System Model for future gravity mission simulation studies. - Journal of Geodesy, 89, 5, p. 505-513. doi.org/10.1007/s00190-014-0787-8
Sasgen, I., Konrad, H., Ivins, E. R., van den Broeke, M. R., Bamber, J. L., Martinec, Z., Klemann, V. (2013): Antarctic ice-mass balance 2002 to 2011: regional re-analysis of GRACE satellite gravimetry measurements with improved estimate of glacial-isostatic adjustment. - The Cryosphere, 7, p. 1499-1512. doi.org/10.5194/tc-7-1499-2013
Current projects:
Observable deformations of the Earth's surface are greatest in areas that were previously covered by ice. A well-studied example is the land uplift in northern Scandinavia, an area that was burdened by a 2 to 3 km thick ice sheet at the last glacial maximum. The still ongoing uplift movement with rates reaching 8 mm/per year near at in the former load center is observed by GPS in the BIFROST project (Baseline Inferences for Fennoscandian Rebound Observations, Sea Level and Tectonics)(Davis & members of BIFROST, 1996; Scherneck et al., 2003). However, present-day ice mass changes also lead to an uplift motion that can be interpreted as GIA. It is important to distinguish between direct elastic and delayed viscoelastic deformations, which is particularly relevant in the Antarctic. In addition, the current deformation state caused by GIA influences the stress field in the formerly glaciated regions.
Reference:
Erfani Jazi, Z., Motagh, M., Klemann, V. (2022): Inferring mass loss by measuring contemporaneous deformation around the Helheim Glacier, southeastern Greenland, using Sentinel-1 InSAR. - Remote Sensing, 14, 16, 3956.
https://doi.org/10.3390/rs14163956
Frick, M., Cacace, M., Klemann, V., Tarasov, L., Scheck-Wenderoth, M. (2022): Hydrogeologic and thermal effects of glaciations on the intracontinental basins in central and northern Europe. - Frontiers in Water, 4, 818469. doi.org/10.3389/frwa.2022.818469
Sasgen, I., Martín-Español, A., Horvath, A., Klemann, V., Petrie, E. J., Wouters, B., Horwath, M., Pail, R., Bamber, J. L., Clarke, P. J., Konrad, H., Drinkwater, M. R. (2017): Joint inversion estimate of regional glacial isostatic adjustment in Antarctica considering a laterally varying Earth structure (ESA STSE Project REGINA). - Geophysical Journal International, 211, 3, p. 1534-1553. doi.org/10.1093/gji/ggx368
Current projects:
... i.e. the movement of the Earth's center of mass relative to the averaged motion of the Earth's surface. The contribution of GIA causes a movement that points in the direction of Northeast America; depending on the Earth's structure, its value is between 0.1 and 1 mm per year. However, the movement of the geocenter is dominated by seasonal fluctuations in the mass redistribution between ocean, land hydrology, atmosphere and within these subsystems.
Reference:
Klemann, V., Martinec, Z. (2011): Contribution of glacial-isostatic adjustment to the geocenter motion. - Tectonophysics, 511, 3-4, p. 99-108. doi.org/10.1016/j.tecto.2009.08.031
... i.e. a movement of the axis of rotation with respect to an earth-fixed reference system (polar motion) and a change in its rotational speed (length of day). Mass redistributions within the Earth and on its surface change the moment of inertia and cause the polar motion. The length of day depends on the main moment of inertia in the direction of the Earth's axis, the so-called J2 term. The polar motion is caused by the ice mass redistribution and leads to a further deformation, which again influences the polar motion. This feedback leads to an average velocity of the pole of a few centimeters per year, which, seen from today's North Pole, points in the direction of eastern Canada. The viscoelastic deformations caused by the polar motion must be taken into account accordingly in the geodetic observables as well as in the sea level. The movement is influenced also by other processes such as mantle convection, present-day mass redistribution at the surface and the pressure field at the core-mantle boundary (e.g. Mitrovica & Vermeersen, 2002).
References:
Martinec, Z., Hagedoorn, J. (2014): The rotational feedback on linear-momentum balance in glacial isostatic adjustment. - Geophysical Journal International, 199, 3, 1823-1846. doi.org/10.1093/gji/ggu369
Martinec, Z., Hagedoorn, J. (2005): Time-domain approach to linearized rotational response of a three-dimensional viscoelastic earth model induced by glacial-isostatic adjustment: I. Inertia-tensor perturbations. - Geophysical Journal International, 163, 2, 443-462. doi.org/10.1111/j.1365-246X.2005.02758.x
In the formerly frozen regions, today's sea level change essentially reflects the post-glacial uplift movement, i.e. the deformation of the earth's surface, resulting in a lowering of local sea level. In the surrounding areas, such as the Netherlands, on the other hand, the sea level rises.
Ice sheets store large quantities of fresh water. Any change in the mass balance of an ice sheet therefore leads to a change in global sea level. During the last glacial maximum, when large ice sheets covered the North American continent and Scandinavia, the globally averaged sea level was almost 120 m below its current level. But even during this time, the resulting changes in ocean load and rotational fluctuations led to temporally and spatially changes in sea level. Reconstructions of the sea level with the help of geological samples, so-called sea level indicators, are an important source of information to quantify the ice mass changes during the glacial cycle as well as to estimate the viscosity distribution in the Earth's interior.
References:
Schachtschneider, R., Saynisch-Wagner, J., Klemann, V., Bagge, M., Thomas, M. (2022): An approach for constraining mantle viscosities through assimilation of palaeo sea level data into a glacial isostatic adjustment model. - Nonlinear Processes in Geophysics, 29, 1, 53-75. doi.org/10.5194/npg-29-53-2022
Bagge, M., Klemann, V., Steinberger, B., Latinovic, M., Thomas, M. (2021): Glacial-isostatic adjustment models using geodynamically constrained 3D Earth structures. - Geochemistry Geophysics Geosystems (G3), 22, 11, e2021GC009853. doi.org/10.1029/2021GC009853
Rosentau, A., Klemann, V., Bennike, O., Steffen, H., Wehr, J., Latinovic, M., Bagge, M., Ojala, A., Berglund, M., Becher, G. P., Schoning, K., Hansson, A., Nielsen, L., Clemmensen, L. B., Hede, M. U., Kroon, A., Pejrup, M., Sander, L., Stattegger, K., Schwarzer, K., Lampe, R., Lampe, M., Uścinowicz, S., Bitinas, A., Grudzinska, I., Vassiljev, J., Nirgi, T., Kublitskiy, Y., Subetto, D. (2021): A Holocene relative sea-level database for the Baltic Sea. - Quaternary Science Reviews, 266, 107071. doi.org/10.1016/j.quascirev.2021.107071
Dobslaw, H., Dill, R., Bagge, M., Klemann, V., Boergens, E., Thomas, M., Dahle, C., Flechtner, F. (2020): Gravitationally consistent mean barystatic sea-level rise from leakage-corrected monthly GRACE data. - Journal of Geophysical Research: Solid Earth, 125, 11, e2020JB020923. doi.org/10.1029/2020JB020923
Palmer, M. D., Gregory, J. M., Bagge, M., Calvert, D., Hagedoorn, J. M., Howard, T., Klemann, V., Lowe, J. A., Roberts, C. D., Slangen, A. B. A., Spada, G. (2020): Exploring the drivers of global and local sea-level change over the 21st century and beyond. - Earth's Future, 8, 9, e2019EF001413. doi.org/10.1029/2019EF001413
Latinovic, M., Klemann, V., Irrgang, C., Bagge, M., von Specht, S., Thomas, M. (2018): A statistical method to validate reconstructions of late-glacial relative sea level - Application to shallow water shells rated as low-grade sea-level indicators. - Climate of the Past Discussions.
doi.org/10.5194/cp-2018-50
Martinec, Z., Klemann, V., van der Wal, W., Riva, R. E. M., Spada, G., Sun, Y., Melini, D., Kachuck, S. B., Barletta, V., Simon, K., James, T. S., G A (2018): A benchmark study of numerical implementations of the sea level equation in GIA modeling. - Geophysical Journal International, 215, 1, 389-414. doi. org/10.1093/gji/ggy280
Düsterhus, A., Rovere, A., Carlson, A. E., Barlow, N. L. M., Bradwell, T., Dutton, A., Gehrels, R., Hibbert, F. D., Hijma, M. P., Horton, B. P., Klemann, V., Kopp, R. E., Sivan, D., Tarasov, L., Törnqvist, T. E. (2016): Palaeo-sea-level and palaeo-ice-sheet databases: problems, strategies, and perspectives. - Climate of the Past, 12, p. 911-921. doi.org/10.5194/cp-12-911-2016
Klemann, V., Heim, B., Bauch, H. A., Wetterich, S., Opel, T. (2015): Sea-level evolution of the Laptev Sea and the East Siberian Sea since the last glacial maximum. - arktos, 1, 1, p. 1-8. doi.org/10.1007/s41063-015-0004-x
Current projects:
The dynamics of the climate on a time scale of tens of thousands of years are affected by changes in the ice sheets and the sea level. Both act as a load that deforms the solid Earth. The deformations thus retroactively influence the climate-relevant surface processes in the atmosphere (changes in topography), in the ocean (changes in bathymetry) and in the ice sheets (changes in sea level at the ice edge and in the bedrock topography).
We focus on numerical modelling of ice sheet dynamics in response to climate variations; we model how the solid Earth responds to the ice mass changes and consider the gravitationally consistent feedback on the ice sheet that includes sea level variations influenced by GIA.
GIA mainly influences processes in the polar regions, as its influence on ice sheet dynamics is dominant. The following mechanisms are relevant:
Ice sheet-ocean:
Ice shelves are in direct contact with the water of the ocean at their bottom side. The temperature and circulation of the water in the ice shelf cavern, that is the volume below the ice shelf, determine the basal melt rates. They influence the thickness of the ice shelf and thus the position of the grounding line of the ice, which has a major influence on the dynamics of the neighbouring grounded ice sheet, its mass balance and thus the global mean sea level. On the other hand, the shape of the ice shelf cavern and the position of the grounding line, as well as the amount of freshwater introduced by melting, have a decisive influence on the circulation of the ocean beneath the ice shelf. Changes in sea level due to local or global processes thus change the size of the cavern, which has a retroactive effect on ice sheet dynamics and ocean circulation.
Ice sheet-atmosphere:
The albedo of the ice surface determines how much solar energy is reflected. Dust, algae growth and the characteristics of the firn are essentially characterised by atmospheric processes. Seasonal changes in temperature and water transport in the atmosphere also influence the mass balance and dynamics of the ice sheet through melting and precipitation rates. Vertical movements of the surrounding ocean surface and the ice sheet base caused by GIA influence the height of the ice relative to the atmosphere and thus the precipitation regime.
GIA primarily influences processes in the polar regions. However, its influence on the global distribution of sea level during a glacial cycle is also relevant, as it controls the drying of continental shelves and the temporally opening and closing of passages such as the Bering Strait or the Sunda Strait, and thus influences global ocean circulation.
Referenzen:
Willeit, M., Calov, R., Talento, S., Greve, R., Bernales, J., Klemann, V., Bagge, M., Ganopolski, A. (2024): Glacial inception through rapid ice area increase driven by albedo and vegetation feedbacks. - Climate of the Past, 20, 597-623. doi.org/10.5194/cp-20-597-2024
Albrecht, T., Bagge, M., Klemann, V. (2024): Feedback mechanisms controlling Antarctic glacial-cycle dynamics simulated with a coupled ice sheet–solid Earth model. - The Cryosphere, 18, 9, 4233-4255. doi.org/10.5194/tc-18-4233-2024
Höning, D., Willeit, M., Calov, R., Klemann, V., Bagge, M., Ganopolski, A. (2023): Multistability and transient response of the Greenland Ice Sheet to anthropogenic CO2 emissions. - Geophysical Research Letters, 50, 6, e2022GL101827. doi.org/10.1029/2022GL101827
Bernales, J., Rogozhina, I., Thomas, M. (2017): Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations. - Journal of Glaciology, 63, 240, 731-744. doi.org/10.1017/jog.2017.42
Timmermann, R., Goeller, S. (2017): Response to Filchner–Ronne Ice Shelf cavity warming in a coupled ocean–ice sheet model – Part 1: the ocean perspective. - Ocean Science, 13, 765-776. https://doi.org/10.5194/os-13-765-2017
Konrad, H., Sasgen, I., Klemann, V., Thoma, M., Grosfeld, K., Martinec, Z. (2016): Sensitivity of grounding-line dynamics to viscoelastic deformation of the solid-earth in an idealized scenario. -Polarforschung, 85, 2, p. 89-99. doi.org/10.2312/polfor.2016.005 | www.polarforschung.de/Inhalt/
Konrad, H., Thoma, M., Sasgen, I., Klemann, V., Grosfeld, K., Barbi, D., Martinec, Z. (2014): The deformational response of a viscoelastic solid earth model coupled to a thermomechanical ice sheet model. - Surveys in Geophysics, 35, 6, p. 1441-1458. doi.org/10.1007/s10712-013-9257-8
Derzeitige Projekte:
