Glacial isostatic adjustment (GIA)
Glacial isostatic adjustment (GIA) describes the adjustment process of the earth to an equilibrium state when loaded by ice sheets. The ongoing adjustment of the earth's body to the redistribution of ice and water masses is evident in various phenomena, which have been studied to infer the extent and amount of the former ice masses, to reconstruct the sea level during a glacial cycle and to constrain rheological properties of the earth's interior.
The glaciation phases during a glacial are characterized by a slow growth of the ice sheets followed by rapid melting. Each 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 today: mantle material that was displaced during the glaciation is still flowing back. This causes the well-known uplift movements in northern Sweden and eastern Canada, which reach one centimeter per year.
... described as deformation of the surface of equal gravitational potential, the geoid. The state of isostatic disequilibrium in regions with past ice-mass loss results in a geoid low; the adjustment process, meaning an influx of mantle material, reduces the geoid low. A well-known example is found in north-eastern Canada, where a geoid low of about 40 m indicates that the earth has not fully regained isostatic equilibrium after the retreat of the Laurentide ice sheet. However, in this region, at least half of the geoid depression is attributed to a density anomaly driving mantle convection (e.g. Mitrovica & Vermeersen, 2002) . The geoid-height changes associated with present-day glacial changes are dominated by the direct attraction of the ice and water masses involved. Changes due to the earth's elastic response are comparatively small.
References:
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. GFZpublic | doi.org/10.5194/tc-7-1499-2013 | PDF |
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. | GFZpublic | doi.org/10.1007/s00190-014-0787-8 | URI | PDF |
Current projects:
A well-studied example is the land uplift taking place in the Gulf of Bothnia, Fennoscandia, an area which was depressed by an ice sheet of 2 to 3 km thickness at the LGM. The ongoing adjustment following the ice sheet's retreat has been monitored by GPS studies, such as the Baseline Inferences for Fennoscandian Rebound Observations, Sea Level and Tectonics (BIFROST) project (Davis & members of BIFROST, 1996; Scherneck et al., 2003). The results determine the vertical and horizontal surface displacements, indicating land-uplift rates of up to 8 mm/a close to the former load centre. In contrast, the deformations in Antarctica has to be separated into recent ice-thickness changes and GIA induced vertical motion.
Referenz:
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 lateral varying Earth structure (ESA STSE Project REGINA). - Geophysical Journal International, 211, 3, p. 1534-1553. | GFZpublic | doi.org/10.1093/gji/ggx368 | URI | PDF |
Derzeitige Projekte:
- PalMod II
... which is the motion of the earth's centre of mass relative to the earth's surface. For this quantity, GIA contributes the dominant secular motion which is directed towards NE America with less than 1 mm/yr velocity, but which is masked by seasonal mass redistributions in ocean, hydrology and atmosphere.
Referenz:
Klemann, V., Martinec, Z. (2011): Contribution of glacial-isostatic adjustment to the geocenter motion. - Tectonophysics, 511, 3-4, p. 99-108. | GFZpublic | doi.org/10.1016/j.tecto.2009.08.031 | PDF
... axis with respect to an earth-fixed system: the true polar wander (TPW) and the duration of a single rotation: the length of day (LOD). Mass redistributions within and on the earth change the inertia tensor of the earth, which is visible as TPW. The LOD is proportional to the moment of inertia about the earth's spin axis, which, in turn, is proportional to the zonal harmonic of degree two of the geopotential. At present, this results in an acceleration of the earth's rotation, i.e. a shortening of the LOD (e.g. Nakada & Okuno, 2003). However, GIA-induced variations of the earth's rotation parameters are masked by other processes, e.g. the convective flow in the mantle, the direct effect of the present redistribution of ice and water masses and changes in the pressure fields at the core-mantle boundary (z.B. Mitrovica & Vermeersen, 2002).
... where, in the formerly glaciated regions, the sea-level falls at rates up to 1 cm/yr. But the relative sea level is rising in the surrounding areas like the Netherlands by a few mm/yr. The present melting of Greenland results in a global sea-level rise. But in the vicinity of Greenland, the sea level drops.
Referenz:
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. https://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. https://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. https://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. https://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. https://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.
https://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 modelling. - Geophysical Journal International, 215, 1, 389-414. https://doi.org/10.1093/gji/ggy280
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. http://doi.org/10.1007/s41063-015-0004-x
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. http://doi.org/10.5194/cp-12-911-2016
Derzeitige Projekte:
Climate dynamic on millenial time scale is affected by changes of ice sheets and of sea level. Both act as loads which deform the solid earth. Vice versa, the deformation affects climate relevant processes in the atmosphere (change in topography), in the ocean (change of bathymetry and coast line) and in the ice sheets (change of sea level at ice margin and bedrock topography).
In response to climate variations, we focus on the numerical modelling of ice-sheet dynamics, assess how the solid earth responses to the respective surface loading and consider, gravitationally consistent, the sea-level change due to mass conservation.
References:
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. | GFZpublic | doi.org/10.2312/polfor.2016.005 | www.polarforschung.de/Inhalt/ | PDF |
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. | GFZpublic | doi.org/10.1007/s10712-013-9257-8 | URI |
Current projects:
Link zu Dynamik von Eisschilden
